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The conformation of two substance P (SP) related hexapeptides. Glp-Phe-Phe-(L-Pro)-Leu-Met.NH2 (I) and Glp-Phe-Phe-(D-Pro)-Leu-Met.NH2 (II), in two solvents, chloroform-d and trifluoroethanol(TFE)-d3/H2O, was studied by two-dimensional NMR methods, including COSY, TOCSY, ROESY and HMQC. The study shows that these two peptides exist predominantly in the extended form in TFE/H2O, but in general exhibit a reverse-turn structure in chloroform. I is clearly less ordered than II in both solvents. Furthermore, extensive Phe3-Pro4 cis==trans isomerization was found in I but not in II. The differences in the conformational behavior of these two peptides, which are selective agonists for neurokinin NK1 and NK2 receptors, respectively, are discussed.

The partition and structure of three adrenocorticotropic hormone peptides ACTH(1–10), ACTH(1–24), and ACTH(11–24) in water and in sodium dodecylsulfate (SDS) and dodecylphosphocholine (DPC) micelles were studied by 2D NMR and NMR gradient diffusion measurements. The diffusion rates, the NH chemical shifts, and the nuclear Overhauser effect patterns provided a coherent picture of binding of these peptides. All three peptides are significantly partitioned in the negatively charged SDS micelles and possess definite secondary structure, as opposed to random structures in water. For ACTH (1–24), the hydrophobic 1–10 segment is partitioned in DPC micelles, but the charged 11–24 segment prefers to remain in the aqueous region. ACTH(11–24) does not bind significantly to the DPC micelles. The binding of the ACTH peptides in these two widely used “membrane mimics” are substantially different from that in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers obtained by attenuated total reflection infrared spectroscopy and from our preliminary diffusion studies of the same peptides in POPC vesicles. This study showed that, in a given micellar medium, all corresponding segments of these peptides are located in the same membrane environment in the system, regardless of whether these segments exist by themselves or are attached to other segments. This result may contradict the membrane-compartments concept of Schwyzer, which suggests that ACTH(1–10) and ACTH(1–24) are located in different membrane compartments because they have different address segments, and consequently, bind to different receptors. The present results also suggest that the assumption that micelles are good membrane mimics should be carefully examined.

6-O-Alkanoylgluconolactones, a novel class of carbohydrate ester-linked surfactants containing a lactone head group, have been synthesized enzymatically from the unprotected aldonolactone. The synthesis was accomplished by regioselective esterification of glucono-1,5-lactones at C-6 by porcine pancreatic lipase in the solvent pyridine. These compounds were found to exhibit a sharp increase in solubility at 90–96°C but remained soluble well below their initial dissolution temperature, precipitating at 30–37°C. To determine the cause of this unusual solubility behavior, the composition of the precipitate was characterized by 1H and 13C NMR, and GC-MS. Analysis of the precipitates identified the material as a hydrolysate containing alkanoylglucono-1,5-lactone, alkanoylglucono-1,4-lactone and alkanoylgluconic acid. The hydrolysis and isomerization of the lactone gave a mixture of compounds that are more soluble than the corresponding pure alkanoylglucon-δ-lactone.

Solasodine and diosgenin have been widely used as starting materials for thepartial synthesis of cortisone, progresterone and C21 steroidal derivatives (oral contraceptives). This study involved the total 1 H and 13 C spectral assignments of these two important compounds by using two-dimensional NMR techniques (COSY, CSCM and HMBC), and resulted in unambiguous spectral assignments, especially in the convoluted regions of the specha ( 1 H, 0.7-2.0 ppm; 13 C, 28-35 ppm)

6-O-Alkanoylgluconolactones, a novel class of carbohydrate ester-linked surfactants containing a lactone head group, have been synthesized enzymatically from the unprotected aldonolactone. The synthesis was accomplished by regioselective esterification of glucono-1,5-lactones at C-6 by porcine pancreatic lipase in the solvent pyridine. These compounds were found to exhibit a sharp increase in solubility at 90–96°C but remained soluble well below their initial dissolution temperature, precipitating at 30–37°C. To determine the cause of this unusual solubility behavior, the composition of the precipitate was characterized by 1H and 13C NMR, and GC-MS. Analysis of the precipitates identified the material as a hydrolysate containing alkanoylglucono-1,5-lactone, alkanoylglucono-1,4-lactone and alkanoylgluconic acid. The hydrolysis and isomerization of the lactone gave a mixture of compounds that are more soluble than the corresponding pure alkanoylglucon-δ-lactone.

The 2 H quadrupolar splitting patterns of selectively deuterium labeled sodium [3,3'- 2 H 4 ]bis(2-ethylhexyl) sulfosuccinate (AOT) in various anisotropic liquid crystalline phases are examined. The complex 2 H spectra are interpreted in terms of the asymmetry of the AOT molecule and the presence of three chiral centers. Due to the former property, the two acyl chains are not equivalent, whereas the latter property produces nonequivalent deuterons within the methylene segments. The effects of the chiral centers are found to be short range. The discussion is extended to include the analogous properties of phospholipids

ACTH (1-10), an adrenocorticotropin hormone fragment, was studied by molecular dynamics (MD) simulation in the NPT ensemble in an explicit sodium dodecylsulfate (SDS) micelle. Initially, distance restraints derived from NMR nuclear Overhauser enhancements were incorporated during the equilibration stage of the simulation. The analyses of the trajectories from the subsequent unrestrained MD showed that ACTH (1-10) does not conform to a helical structure at the micelle-water interface; however, the structure is amphipathic. The loss of the helical structure is due to decreased intramolecular hydrogen bonding accompanied by an increase of hydrogen bonding between the amide hydrogens of the peptide and the micelle head-groups. ACTH (1-10) was found to lie on the surface of the SDS micelle. Most of the hydrophobic interactions came from the side-chains of Met-4, Phe-7 and Trp-9. The peptide bonds were either hydrated or involved in intramolecular hydrogen bonding. Decreased hydration for the backbone of His-6 and Phe-7 was due to intermolecular hydrogen bonding with the SDS head-groups. The time correlation functions of the N-H bonds of the peptide in water and in the micelle showed that the motions of the peptide, except for the N- and C-termini, are significantly reduced when partitioned in the micelle.

Four steroidal glycoalkaloids, solasonine [2], solamargine [3], khasianine [4], and ravifoline [5], with solasodine [1] as the aglycone moiety, have been isolated from Solanum platanifolium. The present study involved the characterization of the novel compound 5 by one- and two-dimensional nmr techniques and has also led to the unambiguous and total 13C- and 1H-nmr assignments of all of these steroidal glycoalkaloids and the direct elucidation of their glycosidic linkages.

Etude par spectrometrie RMN, de la dynamique moleculaire et de l'agregation dans les solutions micellaires de bromure d'hexadecyltrimethylammonium (CTAB) et de salicylate de sodium

The molecular dynamics have been investigated in the lyotropic liquid crystal system consisting of 70 per cent rubidium stearate/30 per cent water using 2H N.M.R. Spectra of 2H2O, perdeuterated rubidium stearate and rubidium stearate selectively deuterated at carbon positions 2, 3, 13 and 18 have been obtained over the temperature range from -80 to 120°C. In the L x phase above 58°C the molecular motions of the lipids are all fast on a time scale of 10-6 s and the observed deuteron quadrupole splittings are a direct measure of the C-D bond order parameter at each carbon position down the chain. The characteristic order parameter profile showing the expected decrease in order from the lipid-water interface to the centre of the bilayer is observed in the L α phase. The dominant molecular motion in the L β phase is rotation of the lipid molecule about its long axis. The correlation time for this motion is smaller than 10-7 s throughout the L β phase. Some trans-gauche isomerization does occur but with a high...

1517, 1446, 1308, 1167 cm-’. Anal. Calcd. for CI9Hl9NO5: C, 66.85; H, 5.61; N , 4.10. Found: C, 66.87; H, 5.76; N, 4.03. Fluorescence Efficiencies. Fluorescence efficiencies of methyl ester 3 and ethyl ester 4 were determined as follows. An airsaturated solution of coumarin 343 was prepared in chloroform having an absorbance CO.10 at 448 nm. The ‘Po was determined by direct comparison with an ethanol solution of coumarin 343 having a similar ab~orbance.~ A solution of ester 3 or 4 in a chosen solvent was prepared and diluted until the absorbance maximum for the ester solution was the same as that of the chloroform solution of coumarin 343. The fluorescence emission spectra for both solutions were recorded with the excitation wavelength set at the wavelength where their absorbance spectra were identical to eliminate the need to correct for the spectral output of the excitation lamp. Fluorescence lifetimes were measured by the phase delay and modulation method. Air-saturated solutions of the esters were prepared in the chosen solvent so that the absorbance at 442 nm was less than 0.10. The samples were irradiated with the 442-nm line from a heliumedmium laser modulated with a Pockel’s cell. An aqueous solution of Ficoll (Sigma) was used as the blank for zero lifetime. Scatter was eliminated from the sample by removing all light below 480 nm with a UV cutoff filter. Data were taken at 1, 5, 10, 20, 30, 50, 80, 100, and 150 MHz and were analyzed by using the ISS 178 software package.

Sequential tritylation, benzoylation, and detritylation of methyl 3-deoxy-3-fluoro-beta-D-galactopyranoside gave crystalline methyl 2,4-di-O-benzoyl-3-deoxy-3-fluoro-beta-D-galactopyranoside (9), which was used as the initial nucleophile in the synthesis of the target oligosaccharide (16). Treatment of 9 with 2,3,4-tri-O-benzoyl-6-O-bromoacetyl-alpha-D-galactopyranosyl bromide gave the corresponding disaccharide derivative 13, having a selectively removable blocking group at O-6'. Debromoacetylation of 13 afforded the disaccharide nucleophile 14 which, when treated with 2,4,6-tri-O-benzoyl-3-deoxy-3-fluoro-alpha-D-galactopyranosyl bromide, gave the fully protected trisaccharide 15. Debenzoylation of 15 gave the title glycoside 16. Condensation reactions were performed with silver trifluoromethane-sulfonate as a promoter in the presence of sym-collidine under base-deficient conditions, and gave excellent yields of the desired beta(trans)-products. Analyses of the 1H- and 13C-n.m.r. spectra, as well as determination of the JCF and JHF coupling constants, were made by using various one- and two-dimensional n.m.r. techniques.

Determination de la dimension des micelles, du nombre d'agregation et la capacite de solubilisation des solutions micellaires

Fourier-transformed infrared spectroscopy (FTIR) and molecular dynamics (MD) simulation results are presented to support our hypothesis that the conformation and the oligomeric state of the HIV-1 gp41 fusion domain or fusion peptide (gp41-FP) are determined by the membrane surface area per lipid (APL), which is affected by the membrane curvature. FTIR of the gp41-FP in the Aerosol-OT (AOT) reversed micellar system showed that as APL decreases from approximately 50 to 35 A2 by varying the AOT/water ratio, the FP changes from the monomeric alpha-helical to the oligomeric beta-sheet structure. MD simulations in POPE lipid bilayer systems showed that as the APL decreases by applying a negative surface tension, helical monomers start to unfold into turn-like structures. Furthermore, an increase in the applied lateral pressure during nonequilibrium MD simulations favored the formation of beta-sheet structure. These results provide better insight into the relationship between the structures of the gp41-FP and the membrane, which is essential in understanding the membrane fusion process. The implication of the results of this work on what is the fusogenic structure of the HIV-1 FP is discussed.

Interaction of 4-methylpyridine with n-butyl-lithium in THF affords a 67:33 mixture of the 1,2-nucleo-philic addition product and the laterally metalated derivative of the heterocycle, respectively, as shown by 13C and 15N n.m.r. spectroscopy. While mixtures were also obtained from 4-methylpyridine and methyl- or t-butyl-lithium. only metalation was realized with the lithium salts of di-isopropylamine and 2,2,6,6- tetramethylpiperidine. A regular trend was noted with other 4-alkylpyridines and n-butyl-lithium culminating in exclusive 1,2-addition on 4-n-butylpyridine. The 13C n.m.r. spectrum from 2-methyl-pyridine and n-butyl-lithium also showed the presence of both addition and metalation derivatives; however, the former material was present only to the extent of 3%.