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5,5'-Dicarboxy-3,3'-dipyrrolyl sulfide was condensed with 5,5'-diformyl-3,3'-dipyrrolyl sulfide or 5,5'-diformyldipyrromethane under acidic conditions to produce, in high yields, macrocycles containing four dipyrromethene units. Key words: 3,3-dipyrrolyl sulfide, cyclopolypyrrole, dipyrromethene, macrocycle.

We have made a comparative study of the dediazoniation of p-hydroxy and p-nitrobenzenediazonium ions. The electron-withdrawing and donating properties of the -N[O.sub.2] and -OH groups strongly determine the reactivity of both compounds, thus exerting different influences upon the dediazoniation reaction. We describe here how the decomposition of p-hydroxy and p-nitrobenzenediazonium ions in a neutral aqueous medium follows a different pattern in the presence of the metal-chelator diethylenetriaminepentaacetic acid (DTPA). The decomposition rate of p-hydroxybenzenediazonium decreases whilst the decomposition of the p-nitrobenzenediazonium ion is enhanced. The experimental data are discussed with reference to a common scheme of interference for both benzenediazonium ions in the light of the radical-scavenging capacity of DTPA. Key words: p-hydroxybenzenediazonium ion, p-nitrobenzenediazonium ion, di-ethylenetriaminepentaacetic acid, dediazoniation, radical scavenging, artifacts.

The photochemical and photophysical behavior of the aqueous uranyl ion [[U[O.sub.2][([H.sub.2]O).sub.5]].sup.2+] has been studied under the influence of visible light and with added perchloric acid over the range of 0.01-4 M. In the presence of 2-methylpropane (isobutane), photo-oxygenation of isobutane occurs to yield, as the major product, 2-methyl-2-propanol (tert-butyl alcohol) along with lesser amounts of 2-methyl-2-propene (isobutene) and other C1-C8 products. The quantum yield for formation of tert-butyl alcohol is independent of light intensity at the irradiation wavelength of 415 nm and of uranyl concentration, but it increases from 0.016 [+ or -] 0.001 M HCl[O.sub.4] (pH 2) to 0.13 [+ or -] 0.01 at 4 M at HCl[O.sub.4]. The emission spectrum from the electronically excited uranyl ion and the associated quantum yields have been measured in the presence and absence of isobutane, as a function of added perchloric acid. While in both cases the shape of the spectrum remains invariant, the quantum yields increase with increasing perchloric acid concentration. The strong dependence on added perchloric acid is interpreted within the context of the presence and interconversion of two electronically excited species, an acid form, *[[U[O.sub.2][([H.sub.2]O).sub.5]].sup.2+], and a base form, *[[U[O.sub.2][([H.sub.2]O).sub.n](OH)].sup.+] . It is proposed that both forms react with isobutane to give a tert-butyl radical, and that oxidation of coordinated aqua ligands occur, the latter generating a hydroxyl radical whose reaction with isobutane rapidly leads also to a tert-butyl radical. The reaction of this alkyl radical with ground-state [[U[O.sub.2][([H.sub.2]O).sub.5]].sup.2+] then gives rise to the stable tert-butyl alcohol product and reduced forms of uranyl ion. Based upon the values of the quantum yields and of excited-state lifetime measurements reported in the literature, a comprehensive mechanism has been developed in a quantitative manner to provide calculated values of the rate constants for the individual mechanistic steps. The calculated rate constants provide a basis to calculate the values of quantum yields for emission and chemical reaction, as well as for lifetimes, that agree very satisfactorily with the experimental values over a 400-fold concentration change in added perchloric acid. Key words: photo-oxidation, photo-oxygenation, uranyl ion, isobutane, tert-butyl alcohol, lifetime, quantum yield, acid-base dissociation.

The oxidation of D-lactose, D-maltose, D-melibiose, and D-cellobiose by [Cr.sup.VI] yields the corresponding aldobionic acid and [Cr.sup.3+] as final products when an excess of reducing disaccharide over [Cr.sup.VI] is used. The rate law for the [Cr.sup.VI] oxidation reaction is expressed by -d[[Cr.sup.VI]]dt = k.sub.H [disaccharide][[Cr.sup.VI]], where the second-order kinetic constant, k.sub.H, depends on [[H.sup.+]]. The relative reactivity of the disaccharides with [Cr.sup.VI] is expressed as follows: Mel > Lac > Cel> Mal, at 33[degrees]C. In acid medium, intermediate [Cr.sup.V] forms and reacts with the substrate faster than [Cr.sup.VI]. The EPR spectra show that five- and six-coordinate oxo-[Cr.sup.V] intermediates are formed, with the disaccharide acting as bidentate ligand. Five-coordinate oxo-[Cr.sup.V] species are present at any [[H.sup.+]], whereas six-coordinate ones are observed only at pH < 2, where they rapidly decompose to the redox products. In the pH 3-7 range, where hexa-coordinate oxo-[Cr.sup.V] species are not observed, [Cr.sup.V] complexes are stable enough to remain in solution from several days to several months. Key words: chromium, saccharides, kinetics, EPR.

Research has been conducted on S-nitrosocysteine. Results demonstrate that formation of this compound in aqueous solution via the use of sodium nitrite and cysteine depends on the pH.

Research has been conducted on indoles. The methods developed for the conjugate addition of these indoles to 2,5-dichlorobenzoquinone are described.

Research has been conducted on the N,N'-dimethyl-1,2-diphenylethane-1,2-diamine. The preparation of the water-soluble version of this compound via the phosphonic acid moiety introduction on the aromatic ring para position is described.

Research has been conducted on spiropentyl acetate and spiropentylcarboxylic acid methyl ester, the chiral monosubstituted derivatives of spiropentane. The synthesis of these compounds in optically active form has been carried out and the results of their conformational and configurational analysis performed via the use of vibrational dichroism and infrared spectroscopies are discussed.

Research has been conducted on Z-phenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole. The study of this compound has been performed in dioxane and water and the results demonstrate the occurrence of a catalyzed pathway in the acidic and basic regions.

Research has been conducted on the polyfunctional compounds with 4,6-dialkoxy-7-arylthioheptene moiety. The selectivity data of the Lewis acid induced transformations of these compounds and the routes which lead to the production of compounds with 1,3-diene/cyclohexane are discussed.

Research has been conducted on the polyhydroxylated sulfinimines. Results indicate that these compounds undergo sulfinimine-mediated Strecker reaction in producing alpha-amino nitriles and that the hydrolysis of these nitriles affords lactone instead of polyoxamic acid.

Research has been conducted on the dicationic palladium cluster Pd (sub)3 (dppm) (sub)3 (CO) (super)2+, where dppm is bis(diphenylphosphino)methane. The reaction of this cluster with acid chlorides performed to afford chloride adduct Pd (sub)3 (dppm) (sub)3 (CO)(Cl) (super)+ and acyl cation as organic counterpart is described.

Research has been conducted on the anilides. The reaction of these compounds with phenyliodine(III) bis(trifluoroacetate) in trifluoroacetic acid or hexafluoroisopropyl alcohol has been investigated and the details are reported.

Reaction of 1,8-bis(trimethylstannyl)naphthalene (1) with an excess of BC[l.sub.3] at -78[degrees], followed by warming to 0[degrees]C, results in the exclusive formation of the novel bifunctional Lewis acid 1-(chlorodimethylstannyl)-8-(dichloroboryl)naphthalene (2), a compound in which a boryl and a stannyl moiety coexist at the peri-positions of a naphthalene core. At elevated temperature compound 2 undergoes a chloride-methyl exchange, which affords 1-(dichloromethylstannyl)-8-(chloromethylboryl)naphthalene (3). Compounds 2 and 3 have been characterized by multi-nuclear NMR spectroscopy. The single crystal X-ray analysis for compound 3 reveals a sterically crowded structure with an essentially trigonal planar boron center, and a tin center pentacoordinated in a [4+1]-fashion. Upon exposure to traces of water, compound 3 is converted into the borinic acid derivative 1-(dichloromethylstannyl)-8-(hydroxymethylboryl)naphthalene (4), which has been characterized by multi-nuclear NMR spectroscopy and single crystal X-ray analysis. Key words: multidentate Lewis acids, organoboranes, organostannanes.

The inclusion of the antibacterial drug nalidixic acid (NAL) in [alpha]- and [beta]-cyclodextrin (CD) cavities was studied using UV--vis absorption and voltammetric methods. It was corroborated that the UV absorption bands of NAL are intensified in the presence of [alpha]- and [beta]-CDs. A pronounced decrease in the peak currents of NAL was also noticed upon the addition of [alpha]- and [beta]-CDs. From the changes in the peak currents, it was concluded that NAL forms 1:1 inclusion complexes with the various hosts, which is also revealed in the phase solubility profile of the NAL-[beta]-CD system, as a representative example. From voltammetric data, the logarithm of the binding constants were calculated to be 2.60 and 3.20 for [alpha]- and [beta]-CDs, respectively. The magnitude of the formation constants, as well as the Gibbs free energies for NAL with [alpha]- and [beta]-CDs, shows that NAL is bound more strongly to [beta]-CD, with a more apolar cavity, than to [alpha]-CD. These observations suggest that hydrophobic interaction is the most important recognition element in the binding process. All orientations of entering NAL into the cavity have been considered herein, with the purpose of characterizing the inclusion complex of NAL with CD. Combining the experimental results and molecular modeling and energy calculations on the inclusion complexes yielded a more detailed picture of the solution structure of the complex formed between NAL and either [alpha]-CD or [beta]-CD. It was inferred that the inclusion process can occur through the 2-methylpyridine side. An additional hydrogen bond was also found to be formed between the carboxyl group of NAL, which remains outside the [beta]-CD cavity, and the secondary hydroxyl group of [beta]-CD. This hydrogen bond should, therefore, be operating as an important second recognition element in the NAL--[beta]-CD system. Key words: cyclodextrins, host-guest association, inclusion complexes, nalidixic acid, solubility, voltammetry.

Solutions of Sb[F.sub.5] in HS[O.sub.3]F with [x.sub.[SbF.sub.5]] = 0.012 to 0.405 are studied by 500 MHz [sup.1]H NMR (299 K) and 471 MHz [sup.19]F NMR (213-250 K), using NMR tubes fitted with fluoropolymer lining. The initial process during dissolution is the fast solvolysis of monomeric Sb[F.sub.5] in HS[O.sub.3]F according to Sb[F.sub.5] + nHS[O.sub.3]F [right arrow] + Sb[F.sub.5-n] [(S[O.sub.3]F).sub.n] + nHF (n = 1, 2). All HF formed during solvolysis will no longer be removed by reaction with glass, but will remain in the superacid system. Besides participation in the fast formation of various fluoro-fluorosulfato anions [[Sb[F.sub.6 - n] [(S[O.sub.3]F).sub.n]].sup.-] (n = 0, 1, 2) and acidium ions [[H.sub.2]X].sup.+.sub.(solv.)] (X = F, S[O.sub.3]F), HF is involved in slow-exchange reactions of the type [[Sb[F.sub.6 - n][(S[O.sub.3]F).sub.n]].sup.-.sub.(solv.)] + HF [right arrow] [[Sb[F.sub.7 - n][(S[O.sub.3]F).sub.n - 1]].sup.-.sub.(solv.)] + HS[O.sub.3]F (n = 1, 2) detected because of a delay of 3 months between sample preparation and measurements and confirmed by repeating theses measurements after a further 3 months. There are three notable differences to our earlier study, affecting concentrations of the fluoro-fluorosulfato antimonate anions observed: (i) in dilute solutions [[Sb[F.sub.6]].sup.-] is formed in high concentrations (34.7 -76.1%), with [[S[b.sub.2][F.sub.11]].sup.-] now clearly detected at intermediate to high Sb[F.sub.5] concentrations (up to 5.8%); (ii) bis-fluorosulfato anions (cis-, trans-[[Sb[F.sub.4][(S[O.sub.3]F).sub.2].sup.-]) are found in much lower concentrations only, which decrease further with time, while tris-fluorosulfato anions ([[Sb[F.sub.3][(S[O.sub.3]F).sub.3]].sup.-]) are now no longer observed; (iii) these reduced concentrations of polyfluorosulfato anions in dilute solutions are responsible for the formation of fewer [micro]-S[O.sub.3]F-oligomers at lower concentrations, when more Sb[F.sub.5] is added. As a consequence, the HS[O.sub.3]F-Sb[F.sub.5] magic acid system is now less complex than found previously and only seven anionic species are clearly observed. Key words: superacids, antimony(V) fluoroanions, [sup.1]H NMR, [sup.19]F NMR, solvolysis.

The capsular polysaccharide of E. coli K92 (K92P) contains elements in common with the capsular polysaccharides of both groups B and C N. meningitidis, and may therefore form the basis of a bivalent vaccine. In an attempt to augment the cross-protective immune response to group B meningococci, the N-acetyl groups of the K92P were replaced by N-propionyl groups (NPrK92P) and conjugated to protein. This strategy had previously been applied with success to the poorly immunogenic capsular polysaccharide of group B meningococcus (GBMP), and the bactericidal epitope was found to be exclusively mimicked by extended helical segments of the NPrGBMP. The NPrK92P-conjugate, in relation to a K92P-conjugate, failed to enhance the response to GBMP but did generate a measurable response to NPrGBMP, but only at the expense of a greatly reduced GCMP response. Despite the presence of an immune response to NPrGBMP, the anti-NPrK92 serum was not bactericidal. Competitive inhibition studies with NPrGBMP oligosaccharides suggested the NPrK92 antibodies could not cross-react with the protective epitope on group B meningococci, as defined by extended helical segments of the NPrGBMP, but only recognized short non-bactericidal NPrGBMP epitopes. This hypothesis was supported from the conformational and molecular dynamics studies of the K92P, which demonstrated a lack of extended conformations that resemble the GBMP extended epitope. Indeed, the conformational properties of the K92P more closely resembled those of the GCMP, thereby explaining the observed moderate cross-protection of the K92P antiserum towards group C meningococci. Thus, on the basis of these results, it can be concluded that K92P, regardless of N-propionyl modification, will not serve as an effective single vaccine component against both groups B and C meningococci. Key words: conjugate vaccine, Neisseria meningitidis, polysialic acid, NMR, molecular dynamics.

Indoles that bear an alkyl substituent in the 3-position, when treated with cyclopropanediesters, typically undergo a [3 + 2]-annulation reaction in a kinetically controlled process (1[right arrow]4). If the reaction is performed at elevated temperatures for a longer period of time, a rearrangement of the putative intermediate 3 occurs in which the alkylating species undergoes a migration to the 2-position followed by loss of a proton to reform the benzopyrrole ring. The yields range from 78 to 10%. If a 3-allylindole is used in combination with a cyclopropanediester, which is further substituted with an alkenyl moiety, the product is an effective ring closing metathesis substrate and can be converted to the 1,3,3a,4,5,6-hexahydro-1H-pyrido[3,2,1-jk]carbazole system. A mechanistic discussion of the rearrangement process is presented. Key words: indole, cyclopropanediester, Lewis acid, ytterbium triflate, rearrangement.

The [alpha]-D-mannopyranosyl and 3,6-di-O-([alpha]-D-mannopyranosyl)-[alpha]-D-mannopyranosyl neoglycolipids 3-6 and the branched and cluster trimannosidic acids 38 and 41 have been made in connection with studies of liposomes as transporters of antigens to dendritic cells. Key words: mannotrioside, trimannoside, neoglycoconjugate, glycolipid, synthesis.

An efficient and inexpensive method for large-scale preparation of [alpha]-D-(l[right arrow]4)-oligogalacturonic acids (oligo-GalA), up to DP 5, from pectic acid is described. Pectic acid was digested with a commercially available pectinase to yield a mixture of oligo-GalA, which was effectively separated by a combination of low-pressure--size-exclusion chromatography based on ion-exchange chromatography to obtain pure oligo-GalA of DP 2-5. Key words: pectic acid, galacturonic acid, galabiose, galatriose, pectinase.

Based on kinetic data of thermal gas-phase elimination reactions, the following Arrhenius log A ([s.sup.-1]) and [E.sub.a] (kJ [mol.sup.-1]) values, respectively, are obtained: 10.76 and 153.5 for 3-thiopheneacetic acid (1), 10.08 and 149.4 for 2-thiopheneacetic acid (2), 12.04 and 207.1 for 2-(3-thienyl)ethanol (3), 11.55 and 203.3 for 2-(2-thienyl)ethanol (4), 10.91 and 123.4 for 2-thiopheneglyoxylic acid (5), 11.05 and 223.8 for l-(2-thienyl)propan-l-one (6), and 10.33 and 149.8 for 3-thiophenemalonic acid (7).The products of these pyrolytic reactions were either carbon dioxide or formaldehyde in addition to methylthiophene or thiophenecarboxaldehyde. Both positional and molecular reactivities of the substrates and related compounds are compared, and the results are rationalized on the basis of a reaction pathway involving a concerted six-membered transition state. Key words: thiophenes, gas-phase, pyrolysis, kinetics, mechanism.

Rates of acid-catalyzed hydrolysis of 3-diazobenzofuran-2-one, measured in concentrated aqueous perchloric acid and hydrochloric acid solutions, were found to correlate well with the Cox-Yates [X.sub.o] excess acidity function, giving [[kappa].sub.[ETA]+] = 1.66 x [10.sup.-4][M.sup.-1][s.sup.-1], m[double dagger] = 0.86 and [[kappa].sub.H+]/[[kappa].sub.D] = 2.04. The normal direction [[kappa].sub.H]/[[kappa].sub.D] > 1) of this isotope effect indicates that hydrolysis occurs by rate-determining protonation of the substrate on its diazois-carbon atom. It was found previously that the next higher homolog of the present substrate, 4-diazoisochroman-3-one, also undergoes hydrolysis by this reaction mechanism but with a rate constant 15 times greater than that for the present substrate; this difference in reactivity can be understood in terms of the various resonance forms that contribute to the structures of these substrates. The product of the present hydrolysis reaction is 3-hydroxybenzofuran-2-one, which itself quickly undergoes subsequent acid-catalyzed hydrolysis to 2-hydroxymandelic acid. The acidity dependence of this subsequent hydrolysis is much shallower than that of the diazo compound precursor, and rates of reaction correlate as well with [[H.sup.+]] as with [X.sub.o]. This is due in part to incursion of a nonproductive protonation on the hydroxy group of 3-hydroxybenzofuran-2-one that impedes hydrolysis and produces saturation of acid catalysis. Rates of hydrolysis of the hydroxy compound were also measured in dilute HCI[O.sub.4] and NaOH solutions as well as in C[H.sub.3]C[O.sub.2]H, [H.sub.2]P[O.sup.-.sub.4], [(C[H.sub.2]OH).sub.3]CN[H.sup.+.sub.3], and N[H.sup.+.sub.4] buffers, and the rate profile constructed from these data showed the presence of uncatalyzed and hydroxide ion-catalyzed reactions. This hydroxide-ion catalysis became saturated at [NaOH] [congruent to] 0.05 M, implying occurrence of yet another nonproductive substrate ionization. Key words: diazo compound hydrolysis, lactone hydrolysis, Cox-Yates excess acidity, acid catalysis, alcohol protonation.

The structure and stemochemistry of polyoximic acid, a degradation product of polyoxins, was originally designated as trans-3-ethylidene-L-azetidine-2-carboxylic acid. However, total synthesis revealed that the correct structure was in fact cis-3-ethylidene-L-azetidine-2-carboxylic acid, which was confirmed by X-ray crystallography. The synthesis of the trans-isomer was also done and its identity was confirmed by X-ray analysis as well. The key step for constructing the four-membered ring was a rhodium catalyzed carbenoid insertion into the N--H bond of a [beta]-amino acid derivative. The stereoselectivity of the exo-double bond was controlled by conducting a Horner-Emmons-Wadsworth or a Wittig reaction to generate the trans- and cis-isomers, respectively. Weinreb's amide was used as a latent methyl group for the separation of trans and cis mixtures. The double bond stereochemistry of polyoximic acid in the parent polyoxin was also confirmed to be cis by extensive 2D NMR studies. Key words: diazoinsertion, azetidine, olefination.

Suzuki cross-coupling reactions of 3-pyrroleboronic acid derivatives with haloaromatics and the reverse process i.e., the coupling of 3-iodo(bromo)pyrroles with arylboronic acids have been investigated as a potential key step in the synthesis of (-)-rhazinilam and analogues. It was found that 3-iodo-2-formyl-1-tosylpyrroles efficiently coupled with a variety of arylboronic acids in the presence of Pd[Cl.sub.2] (dppf) as catalyst. This catalytic system is compatible with a broad spectrum of arylhoronic acids--electron-rich, electron-poor, hindered, heterocyclic--which easily coupled with the pyrrole substrate. Key words: 2-substituted-3-arylpyrroles, biaryls, coupling reactions, arylboronic acids, palladium coupling, catalysis.

(+)- and (-)-Nephrosteranic acid (16) have been prepared in an enantioselective fashion from alkyne acid 19 (or ent-19) by a three step sequence involving debenzylation-lactonization, oxidative cleavage, and selective epimerization at [C.sub.4]. Acids 19 and ent-19 were obtained as single enantiomers employing a Nicholas-Schreiber reaction. Key words: paraconic acids, nephrosteranic acid, butyrolactones, Nicholas-Schreiber reaction.

A positional isomer of 7-deoxypancratistatin was synthesized in 12 steps from epoxyaziridines 4 and 5. An intermolecular opening of the aziridine rather than the epoxide in the early stages of the synthesis led to 13, which did not match the properties of tetraacetate 10 derived from 7-deoxypancratistatin. At no stage of the synthesis did standard NMR techniques, involving [sup.1]H-[sup.1]H or [sup.1]H-[sup.13]C coupling, prove adequate for the structure assignment. Unambiguous structure was assigned by [sup.1]H-[sup.15]N correlation NMR spectroscopy as well as by the conversion of epoxide 11 to diol 29 synthesized independently by another route. Experimental and spectral details are reported for all new compounds. Key words: [sup.15]N NMR spectroscopy, iso-7-deoxypancratistatin, Lewis acid catalyzed intramolecuar opening of epoxides, aminoconduritols.

Chemical transformation of nitroso acetals derived from tandem [4 + 2]/[3 + 2] cycloadditions of nitroalkenes have been investigated. New reduction methods were surveyed in an attempt to supplant the use of hydrogen and Raney nickel. Homogeneous catalytic hydrogenation was not successful, but samarium diiodide did effectively and selectively cleave one of the N--O bonds in a number of nitroso acetals. Acid-promoted hydrolysis of the nitroso acetals produced both [alpha]-alkoxy nitrones and hydroxamic acids selectively via expected pathways. Key words: nitroso acetals, hydroxamic acids, [alpha]-alkoxy nitrones, reduction, hydrolysis.

BINOL-aluminum complexes were successfully employed as mediators and catalysts in asymmetric Baeyer-Villiger rearrangements of cyclobutanones. Good enantioselectivies were achieved with only 15 mol% of the chosen chiral Lewis acid. The enantiomeric excesses obtained have never been reached before in such metal-catalyzed Baeyer-Villiger reactions. Key words: aluminum, asymmetric catalysis, lactones, oxidations, rearrangement.

A diphenylmethane model compound (2,2'-methylenebis[6-methoxy-4-methylphenol]) and residual kraft lignin were treated with alkaline hydrogen peroxide. Kinetic data for the disappearance of the model and the diphenylmethane structures in the residual lignin was collected. The activation energies for the degradation were found to be similar (54 [+ or -] 11 kJ [mol.sub.-1] for the model and 58 [+ or -] 5 kJ [mol.sub.-1] for the residual lignin). A comparison of the activation energies with the data of a previous study on a biphenyl model compound (3,3'-dimethoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol) showed a substantially higher activation energy for the degradation of the latter. Pathways for the degradation of 2,2'-methylenebis[6-methoxy-4-methylphenol] were proposed and the intermediates subjected to computational analysis using a semiempirical method (PM3). The results suggest that initially a common pathway exists, resulting in 2-[2-hydroxy-3-methoxy-5-methyl-phenylmethyl]-4-methyl-2, 4-hexadienedioic acid. Then the pathway branches into three, resulting in three major degradation products. The main driving force of the reactions is the formation of radical sites after reaction with hydroxyl radicals and subsequent radical coupling with perhydroxyl radicals to form peroxides. All the reactions on the pathways are exothermic except for the transformations of peroxides into dioxetanes. The dioxetanes cleave exothermically resulting in ring cleavage and fragmentation. The computed data permitted for the rationalization as to why the diphenylmethane structures appear to be more labile than biphenyl structures under alkaline oxidative conditions. Key words: activation energy, alkaline oxidative degradation, computational chemistry, lignin, reaction mechanism.

The influence of the entropy on the proton transfer equilibria AH ... B [left and right arrow] A ... H[dagger]B in the dimethylphosphinic acid (DMP)-N-base and in the methanesulfonic acid (MSA)-N-oxide hydrogen bonds is studied by [sub.1.H] NMR spectroscopy as a function of the [delta]p[K.sub.a], i.e., the p[K.sub.a] of the base minus the p[K.sub.a] of the acid. It is shown that with increasing [delta]p[K.sub.a] the proton transfers to the N-oxide acceptor. In the DMP + N-base family of systems, first the double-minimum proton potentials ([delta]H = 0) occurs and only with further increasing [delta][pK.sub.a] do the POH ... H = P[O.sup.minus] ... H[dagger]N equilibria become symmetrical ([delta]G = 0). [delta]G and [delta]H are connected by the Gibbs-Helmholtz equation, [delta]G = [delta]H-T[delta]S. Hence, the reason of this effect is the large negative interaction entropy term ([delta][S.sub.I] arising from the large order around the polar structure, which shifts the equilibria strongly to the left-hand side. With the MSA-N-oxide hydrogen bonds a single--minimum proton potential was found. The minimum shifts with increasing [delta]p[K.sub.a] from the donor to the acceptor of the O ... H[dagger] ... N hydrogen bonds. It is shown that with increasing [delta]p[K.sub.a] the proton potential becomes on average symmetrical, whereas the proton is still largely on the left-hand side. This result is also explained by the large negative interaction entropy due to the order of the environment if the proton is at the acceptor [Beta]. Key words: entropy, hydrogen bonds, infrared, spectroscopy, proton transfer.

Phosphate-Zr[O.sub.2]-[Si.sub.2]O catalysts were synthesized by sol-gel method using tributyl phosphite, zirconium propoxide, and tetraethyl orthosilicate as precursors. They were characterized by [N.sub.2] adsorption, [sup.31.P] CP MAS NMR, and DRIFTS. At lower P content, monomeric phosphates were formed on the surface of the catalysts, which were mainly responsible for the isopropanol dehydration activity. At higher P content, polyphosphates were formed, and thus, the dehydration activity decreased. An optimum P content for dehydration activity was found to be at 10 mol%. Key words: sol-gel synthesis, ternary oxides, phosphate, acid catalyst, alcohol dehydration, [sup.31.P] CP MAS NMR, [N.sub.2] adsorption, DRIFTS.

The reaction of N-salicylidene-2-aminophenolate (SAP-[H.sub.2]) derivatives with phenyl boronic acid afforded five new boron bicyclic species in moderate yields, as confirmed by an X-ray study of the boron heterocycle derived from 2-amino-4-chlorophenol. The results also showed that the boron complexes derived from Schiff bases undergo an acetolysis reaction to give the corresponding dioxazaborocines containing all substituents on the same side also in good yields. The structure of one of the addition products was established by X-ray analysis showing that, in the solid state, it exists as a dimeric structure formed by hydrogen bonds. Key words: borocines, tridentate ligands, imines, boronic acids.

The rates of proton transfer reactions between C-acids of the series of nitroalkanes with increasing bulk of R = H, Me, Et, i-Pr substituent as: 4-nitropbenylnitromethane (0), 1-(4-nitrophenyl)-l-nitroethane (1), 1-(4-nitrophenyl)-1-nitropropane (2), 2-methyl-l-(4-nitrophenyl)-l-nitropropane (3) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-l,5,7-triazabicyclo [4.4.0]dec-5-ene (MTBD) have been measured in acetonitrile at pseudo-first-order conditions. The product of the proton transfer reaction with MTBD in acetonitrile is dissociated into free ions while that of the TBD reaction is composed of a comparable amount of ions and ion pairs. The second-order rate constants [(k.sub.2H)] for these bases of almost equal strength in acetonitrile [(pk.sub.a.] = 24.70, 24.97 for MTBD and TBD) and C-acids 1, 2, and 3 are: 317, 86, 7.6 [dm.sup.3] [mol.sup.-1]; and [s.sup.-l]; and 15 200, 5300, 1100 [dm.sup.3] [mol.sup.-1] [s.sup.-1], respectively. The appropriate primary deuterium kinetic isotope effects [(k.sub.H./k.sub.D) are 12.5, 10.8, 6.9; and 9.9, 11.2, 12.6. The influence of steric hindrance brought by reacting C-acids and bases is discussed. The different structure of the transition states and the products as mono-and double-hydrogen bonded complexes for these series of C-acids and MTBD and TBD bases is manifested by a distinct reaction mechanism which we attempt to explain. Key words: proton transfer, kinetic study, C-acids, organic bases, acetonitrile, kinetic isotope effects.

A series of [beta]-lactam derivatives were synthesized and tested to determine the structure-activity relationship for inhibition of human leukocyte elastase (HLE), a serine protease involved in several degenerative lung and tissue diseases. The most potent [IC.sub.50] values were obtained with neutral hydrophobic 7[alpha]-methoxy cephalosporanic acid derivatives. Tryptophanyl-9-fluorenylmethyl ester and N-benzhydryl piperazine derivatives of 7[alpha]-methoxy cephalosporanic acid represent two novel HLE inhibitors, with length of action persisting beyond 24 h. Key words: [beta]-lactams, neutrophil elastase, protease inhibitors, peptides.

The diborylated ferrocene compound 1,1'-Fc[[B[([C.sub.6][F.sub.5]).sub.2]].sub.2] (2) was prepared via a transmetallation reaction involving 1,1'-Fc[(HgCl).sub.2] and two equivalents of ClB[([C.sub.6][F.sub.5]).sub.2]. Although this reaction is very clean spectroscopically, isolated yields of 2 were never greater than 40% owing to the high solubility of the compound in non-donor solvents. Compound 2 is similar in its properties to the related monoborylated complex FcB[([C.sub.6][F.sub.5]).sub.2] (1) reported previously, particularly the UV-vis spectrum, which exhibits an intense charge transfer absorption ([[lambda].sub.max] = 233 nm, [epsilon] = 1.64 x [10.sup.4]) assignable to an [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] transition. However, 2, is significantly more Lewis acidic than 1, reacting with weak donors such as acetonitrile at room temperature, and effecting methide abstraction from [Cp.sub.2]Zr[Me.sub.2] under mild conditions. Complex 2 also forms a bis(trimethylphosphine) adduct (3), which was structurally characterized via X-ray crystallography. Key words: organoboranes, ferrocene derivatives, multidentate Lewis acids.

A series of new chromophores, styryl-parent end-capped with various donors, and with barbituric acid, methyl-pyridinium, and methyl-quinolinium as the acceptors, have been synthesized and characterized by element analysis or X-ray diffraction. Using the Z-scan system, their two-photon absorption (TPA) cross-section values ([delta]) have been determined under excitation with 10 Hz, and 1064 nm, 35 ps mode-locked Nd: YAG laser pulse in DMF with [d.sub.0] = 0.05 M. The effective [delta] value is as high as 10.9 x [10.sup.-48] [cm.sup.4] s per photon for trans-4-(4'-N,N-diphenyl amino) styryl-N-methyl quinolinium iodide (DPASQI). The [delta] value increases from barbituric acid- to pyridinium- to quinolinium-derivatives apparently due to the increase in both the conjugated degree and planarity; however, when the acceptor is fixed, the [delta] value increases from dialkyl amino groups to dipbenyl amino groups even though the latter is a weaker donor than the dialkyl amino groups. Theoretical calculations confirm that the increased distortion from planarity for the barbituric acid derivative makes its [delta] value decrease. The relatively large [delta] value for quinolinium- or pyridinium-derivatives originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment ([delta][[mu].sub.ge]) between the [S.sub.0] and [S.sub.1], and the transition dipole moment ([M.sub.ee']) between [S.sub.1] and [S.sub.2]. Key words: two-photon absorption, intramolecular charge transfer, styryl-quinolinium, styryl-pyridinium, styryl-barbituric acid.

The addition reactions of organolithium and Grignard reagents to chiral, enantiomerically pure ortho-formyl (arene)tricarbonylchromium acetal complex (2) have been studied. The diastereoselectivity of the addition process is fair in the absence of an additional Lewis acid, and good in the presence of Ti([O.sup.i]Pr)4. The nature of the newly formed chiral centre, and studies on the possible nature of the nucleophilic species suggest that the Lewis acid acts through monodentate coordination to the aldehyde carbonyl, and thereby alters the carbonyl rotamer population more heavily in favour of the s-trans conformation. Nucleophilic attack then occurs on the face anti- to that bearing the Cr[(CO).sub.3] unit. Key words: (arene)tricarbonylchromium complexes, asymmetric synthesis, carbonyl additions, Lewis acids.

[An.sup.IV] [Fe.sup.II] [(CN).sub.6].x[H.sub.2]O (An = Th, U, Np) molecular compounds have been prepared by precipitation from acidic media. These microcrystalline compounds have been characterized by infrared spectroscopy, X-ray diffraction, and X-ray absorption spectroscopy. They have been found to be isostructural with the [Ln.sup.III]K[Fe.sup.II][(CN).sub.6].4[H.sub.2]O compounds. The molecular structures of these compounds are presented and their chemical formulas are given: in all compounds, the Fe[(CN).sub.6] octabedra is conserved and the An ion is linked to the N atoms of the CN ligands. The formal oxidation states are also discussed. Key words: hexacyanoferrate, actinide, EXAFS, XANES, X-ray absorption spectroscopy.

Synthesis has been carried out of diarylboron chelates of 2- and 3-hydroxynitrones, of 2- and 3-hydroxyoximes, and of 2-carboxynitrones and a 2-carboxyoxime. The structures have been determined from spectroscopic data and from X-ray analyses of Sd, 9a, 11b, and 19. Crystals (at 180 K) of 5d are monoclinic, a = 10.543(2), b = 19.085(4), c = 10.2667(3) = [Angstrom], [beta] = 90.4978(7)[degrees], Z = 4, space group P[2.sub.1]/c; those of 9a are orthorhombic, a = 10.9913(5), b = 14.9329(7), c = 10.2460(13) [Angstrom], Z = 4, space group P[2.sub.1] [2.sub.1]2; those of 11b are monoclinic, a = 11.227(2), b = 9.967(2), c = 17.0537(4) [Angstrom], [beta] = 105.4179(5)[degrees], Z = 4, space group P[2.sub.1]/n; those of 19 are monoclinic, a = 11.1847(15), b = 13.715(3), c = 11.5559(5) [Angstrom], [beta] = 104.8730(10)[degrees], Z = 4, space group P[2.sub.1]/n. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R(F, I [greater than or equal to] 3 [sigma](I)) = 0.049, 0.047, 0.042, and 0.047, respectively, for CCD data for 5d, 9a, lib, and 19. The four molecules contain five-, seven-, six-, and five-membered rings, respectively, with O-B-N groups in the Sd, llb, and 19, and O-B-O in 9a; the rings exhibit various deviations from planarity, particularly the seven-membered ring. Key words: diarylboron chelates, hydroxyoximes, hydroxynitrones, carboxyoximes, carboxynitrones, organoboron compounds, crystal structure.

The syntheses of the first examples of selenoparabanic acid derivatives (dialkylimidazolidine-2-selone-4,5-dione, [3e.sup.R], R = Me, Et, Bu) are presented along with the X-ray crystal structure determination of 3[e.sup.Et]. To gain an insight in the properties of parabanic acid derivatives on the basis of their electronic structures, we report the results of comparative hybrid-DFT calculations performed on parabanic, thioparabanic, and selenoparabanic acids ([3a.sup.H], [3b.sup.H], and [3e.sup.H] and on their N,N'-dimethyl derivatives [3a.sup.Me], [3b.sup.Me], and [3e.sup.Me]. Calculations show that the different nature of the frontier orbitals of [3a.sup.R] compared to those of [3b.sup.R] and [3e.sup.R], might account for the different reactivities of these compounds. Moreover, the weak donor character of [3b.sup.R] and [3e.sup.R] towards molecular di-iodine, estimated by FT-Raman measurements is in agreement with the calculated NBO-charge distribution. Key words: selenation, selenoparabanic derivatives, crystal structure, DFT calculations.

The intramolecular Diels-Alder reaction of furanyl amides derived from 2-furylacetic acid has been examined. Substrates containing either an imide or tertiary amide linkage between the furan and the dienophile underwent smooth cycloaddition upon thermolysis. By varying the reaction conditions, either the primary cycloadduct or the ring-opened and acetylated product could be isolated in excellent yield. The stereochemical outcome of the IMDAF cycloaddition has the side arm of the tethered alkenyl group oriented syn with respect to the oxygen bridge. Semi-empirical AM1 calculations show that the exo-cycloadduct is 11 kcal lower in energy than the corresponding endo adduct and, presumably, some of this energy difference is reflected in the transition state for the cycloaddition. The IMDAF reaction of N-allyl-[2-(3,4-dimethoxyphenethyl)]-2-furanyl-2-yl-acetamide proceeded in 90% yield upon heating in xylene. The 4+2-cycloadduct undergoes ring-opening on treatment with base and the resulting alcohol was converted into the corresponding benzyl ether. Raney nickel reduction followed by Bischler-Napieralski cyclization furnished the tetracyclic skeleton of the berberine alkaloids. Key words: intramolecular, cycloaddition, Diels-Alder, furanylamide, heterocycle.

A series of aminodiols RN[(C[H.sub.2]C[H.sub.2]C(OH)[R'.sub.2]).sub.2] (R, R'=Me, Me 4; Me, Ph 5; tert-butyl, Me 6; tert-Bu, Ph 7; (S)-PhCH(Me), Me 8) were prepared by the Michael addition of a primary amine to methyl acrylate followed by reaction of the resulting aminodiester with excess methyl or phenyl lithium. Reaction of two equivalents of the aminodiols 4-8 with tetrabenzylzirconium afforded the zirconium bis(aminodiolates) 10--14 in excellent yield. Complex 11 (R, R'=Me, Ph) adopts a cis, fac-octahedral geometry in solution and in the solid state. Complexes 10-14 are fluxional in solution by NMR spectroscopy: small substituents at nitrogen and large substituents at the alkoxide carbons slow the rate of exchange. The chiral complex 14 functions as a Lewis acid catalyst in the nitroaldol (Henry) reaction and the oxidation of geraniol by ten-butyl hydroperoxide with modest enantioselectivities (30 and 46% enantiomeric excess (ee), respectively). Key words: diol, Michael addition, zirconium, synthesis, structure, fluxional, alkoxide, Lewis acid, catalysis.

The cis and trans isomers of 2-(3-phenylthioureido)cyclopentanecarbonitrile, 1, and the respective carboxamides, 3, and acids, 4, have been prepared. Acid cyclization of bothnitriles, faster with the cis isomer, gave the more stable cis-2-thiooxo-cyclopenta[d]pyrimidin-4-one, 7. In base cis-1 formed the cis 4-imino-2-thiooxopyrimidine 2 which in aqueous alkali broke down via 3 to the acid 4; while in the presence of 66% acetonitrile 2 rearranged to the 4-phenyliminopyrimidine 5 to give as final product the thioureido acid 6 carrying no phenyl group. The [.sup.1H] NMR data for imino and phenylimino derivatives 2 and 5 showed strong bias for conformation A with 1-N pseudoaxial in the cyclopentane ring. Spectra of the E and Z isomers of the iminopyrimidine 2 under slow exchange could be recorded in DMSO-[d.sub.6]. The phenylimino tautomer of 5 is observed in C[D.sub.3]OD and in CD[Cl.sub.3] with the E and Z isomers in a 1:1 ratio. In DMSO-[d.sub.6] the phenylamino tautomer 5a is also detected. The first process in aqueous KOH, the conversion of nitrile cis-1 into the imino intermediate 2, reaches an equilibrium which shifts towards the nitrile at higher allkalinities because of ionization of the phenylthioureido group ([K.sub.e] = [2]/[1] = 2.43 and p[K.sub.AH] = 12.74). The cyclization of 1 to 2 is first order in [OH.sup.-] while the slower breakdown of 2 is pH independent. The latter is [10.sup.4] times faster than the hydrolysis of acetonitrile evidencing substantial anchimeric assistance. The change in the reaction route towards the rearranged phenyliminopyrimidine 5 upon addition of acetonitrile can be caused by the lower dielectric constant favouring the elimination step leading to the intermediate isothiocyanate, and by increased activity of O[H.sup.-] accelerating the (presumably) second order elimination step as opposed to the pH-independent hydrolysis of the imino derivative 2. Key words: anchimeric assistance, phenylthioureido nitriles, iminothiooxopyrimidine tautomers, alkaline hydrolysis, solvent effects.

The titration of NaOH by HCl is achieved through infrared spectral measurement of the various mixtures. Factor Analysis (FA) is used to separate the spectra. Four principal spectra were necessary to perform the analysis: pure water, 2.09 M HCl, 2.23 M NaOH, and 2.60 M NaCl solvated water. Each of the 18 experimental spectra obtained was determined to be a linear combination of these principal spectra. The composition of the solutions retrieved from the IR analysis is identical to what was determined by the mass balance. The mean activity coefficient of HCl was calculated using the concentration of HCl obtained by IR and the activity obtained by pH measurements. It was found that the mean activity coefficient increased by a factor greater than 2 in the presence of 1 M NaCl. Because the water molecules associated to the ionic pair [H.sup.+]/[Cl.sup.-], as observed by IR, are unmodified by the presence of the salt, such an increase cannot be attributed to a modification of the strong association of the water molecules to the pair of ions. Key words: infrared spectroscopy; ATR; liquid; acidic solutions; alkaline solutions; aqueous solutions; factor analysis; principal spectra; HCl-, NaOH-, NaCl-solvated water; activity coefficient; IR titration.

Research has been conducted on the 1,3-dicarbonyl compounds. The alpha-bromination of these compounds carried out via the Lewis acid and N-bromosuccinimide have been investigated and the details are reported.

The authors have investigated glycosyl phosphinic acids. They describe the method they have developed for the synthesis of these acids from C-phosphonates.

Research has been conducted on stereogenic centers which are required for (+)-discodermolide. The authors describe the synthesis of these centers from racemic aldehyde derived from 2-methyl-1,3-propanediol.

Research has been conducted on vinyl allenes and imines. The authors have investigated the reaction of these compounds carried out under Lewis acid catalysis.

Research has been conducted on 3-hydroxy-2,4,6-trimethylheptanoic acid. The authors report that the diastereomers of this acid have been synthesized from (+)- and (-)-pseudoephedrine propionamide.

Research has been conducted on lithiated bislactim ethers. The authors report that the conjugate addition of these ethers to alpha-, beta- and alpha,beta-substituted vinylphosphonates will lead to stereoselective access to different enantiomerically pure monosubstituted and disubstituted 2-amino-4-phosphonobutanoic acids.