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The 5-amino-3-arylamino-1,2,4-oxadiazoles 2 are conveniently prepared by oxidative cyclization of the arylamidinoureas 10. The process is also capable of producing a variety of the 5-substituted-amino analogs 32 when the appropriately substituted guanidine 31 is employed as the substrate. Two different types of rearrangement leading to triazol-3-ones accompany cyclization depending on the choice of starting material. The structures of the rearranged products were established by X-ray crystallographic analysis and the reaction mechanisms leading to these unexpected products are discussed.

The isolation of three new terpenoid 5-methylcoumarins in the form of diastereomeric mixtures from a north Indian collection of Ethulia conyzoides is reported. Stereochemistries were deduced by X-ray analysis of a pure acetate isomer obtained on acetylation of one of the diastereomeric mixtures.

A simple and high yielding synthesis of metalla-2-indane-1,3-diones (phthaloyl metal complexes) by the insertion of low-valent transition metal complexes (ClRh(PPh3)3, ClCo(PPh3)3, Fe(CO)5) into benzocyclobutenedione is reported. The structure of the rhodium complex was established by an X-ray analysis.

A study of the static stereochemistry of 1,1,2,2-tetraphenyldisilane ( 1 ) and 1,1,2,2-tetramesityldisilane ( 2 ) by empirical force field calculations, X-ray diffraction, and 1 H NMR reveals that the preference for the anti conformation, exhibited by the unclamped 1,1,2,2-tetraarylethanes, is sustained in the analogous disilanes, although in somewhat attenuated form. This anti preference stands in contrast to the gauche preference of 1,1,2,2-tetraalkyldisilanes. Examination of 3 J HH coupling constants for R 2 HSiSiHR 2 ; (R = phenyl, mesityl, 2,6-dimethyl-phenyl, t -butyl, cyclohexyl) suggests the existence of a Karplus relation for H-Si-Si-H systems.

6-Bromo-4-fluoro-1,3-dinitrobenzol ist ein wertvolles Reagens zur Herstellung kristalliner Derivate von Aminen, Phenolen und Alkoholen. Die resultierenden 5-Bromo-2,4-dinitrophenylverbindungen konnen zur Charakterisierung und Kristallstrukturanalyse durch Rontgendiffraktion dienen. Aus den Antibiotika X-5108 und Mocimycin haben wir kurzlich ein neuartiges Octadienal isoliert, das mit 6-Bromo-4-fluoro-l,3-dinitrobenzol reagiert und in das Dimethylacetal umgesetzt wurde. Das resultierende Derivat wurde auf kristallanalytischem Wege als 8-(5-Bromo-2,4-dinitroanilino)-3(S)-methoxy-2(R),4-dimethyl-4(trans),6(trans)-octadienal-dimethylacetal identifiziert.

Die Synthese von 1α, 25-Dihydroxycholesterin (1) aus 3-O-Acetyl-25-hydroxy-cholesterin (2) in 18proz. Gesamtausbeute wird beschrieben. Die Struktur von 1 wurde durch Rontgen-Strahlendiffraktion bewiesen.

Six new diterpene isocyanides have been isolated from a sponge ( Adocia sp.). Their structures support the biosynthetic suggestion for the formation of diisocyanoadociane reported from the same sponge.

The thermodynamic equilibrium between the anomeric coumerosides 3 and 4 differs drastically from that which exists between their C(2)-epimers 7 and 8 . Stability determining factors which govern the position of these equilibria include in addition to steric interactions the Δ2 effect and the anomeric effect. The latter is discussed in terms of orbital overlap between nonbonding electrons on oxygen and anti -bonding σ orbitals. The α-configuration of the glycoside linkages of coumermycin A 1 was secured by X-ray analysis of compound 12 .

The following new cycloartanes were isolated from the aerial parts of Lindheimera texana: (16S,23S)- and (16S,23R)-16,23-epoxycycloart-24-en-3-one, (3S,16S,23S)- and (3S,16S,23R)-16,23-epoxycycloart-24-en-3ol, (16S,23R)-16,23-epoxy-23,25-epidioxycycloartan-3-one, (16S)-23,24,25,26,27-pentanorcycloartan-3-one-16,22-olide, (16S,23S,24R)- or (16S,23R,24S)-23,24-epoxycycloartan-3-one-16,25-diol and (16S,23ζ,24ζ)-cycloartan-3-one-16,23,24,25-tetrol. Structures were established by chemical transformations and spectroscopic methods and, in the case of (16S,23R)-16,23-epoxy-23,25-epidioxycycloartan-3-one, by X-ray crystallography. Norambreinolide, several known labdanes and oleanolic acid were also isolated.

Re-examination of Liatris gracilis afforded the known sesquiterpene lactones chapliatrin, isochapliatrin, acetlisochapliatrin, five new closely related 5,10-epoxygermacranolides and a new eudesmanolide. The stereochemistry of the 5,10-epoxygermacranolides has been settled by an X-ray analysis of isochapliatrin.

The structure of aspersitin, a new metabolite of Aspergillus parasiticus was determined by X-ray analysis, and by spectroscopic measurements.

A bicyclic diterpene cleomeolide (1) C20H30O3 has been isolated from Cleome viscosa L. (Capparaceae), and its stereostructure established by chemical, spectral and X-ray crystallographic means. Crystals of 1 belong to space group P21 with a = 10.329(2)A, b = 12.468(3)A, c= 7.356(2)A,β = 109.98°, and Z = 2. The structure was solved by a multiple solution procedure and refined by full matrix least-squares to give R = 0.041 and wR = 0.051. Oxidation of 1 gave the ketone 4, which on treatment with methanolic KOH led to a facile transannular reaction to give the lactone 6

The crystal structures of the ethylenediamine salts of two diastereoisomeric hydroxycitratesy are described, and their conformations in the solid state are analyzed. In both structures, the HOCCOH torsion angle is approximately 60 ° as found for many tartrates and mesotartrates. The presence of three carboxyl groups and two hydroxyl groups in hydroxycitrates leads to 10 possible types of tridentate metal chelates. Since bacterial citrate lyase and ATP citrate lyase require metal ions, the possible geometries of hydroxycitrate chelation have been compared with those of citrate, and as a result, some information on the geometry of each enzymic active site has been obtained. If the hydroxycitrate binds in the same manner as citrate, the C(3)zC(4) bond will be in the correct position to be cleaved. Other modes of binding of hydroxycitrate, if they can be accommodated in the active site of the enzyme, are nonproductive and compete with the citrate-like mode causing inhibition. It is possible, in these alternate modes of binding of hydroxycitrates, for additional binding to side chains in the active site of the enzyme to occur, resulting in extremely potent inhibition.

The preparation of the title compound from methyl 4,6- O -benzylidene-2- C -methyl-2- O -(methylthio)methyl-α- d - ribo -hexopyranosid-3-ulose and its single-crystal X-ray structural characterisation is described. Consistent with the chemistry of methyl 4,6- O -benzylidene-α- d - ribo -hexopyranosid-3-ulose 1 , the Grignard reduction of the two 2- C -methyl-α- d - ribo -hexopyranosid-3-uloses examined produced allo compounds stereoselectively. Methyl 4,6- O -benzylidene-2,3-di- C -methyl-2- O -(methylthio)methyl-α- d -allopyranoside was dehydrated to the hex-3-enopyranoside 2 , which was converted into methyl 2,3-dideoxy-2,3-di- C -methyl-α- d - glycero -hex-2-enopyranosid-4-ulose by an acid-catalysed fragmentation-process 2 .

Cyclohexenone 3, a synthon for the aureolic acid aglycone, has been prepared using D-fucose and trimethylsilyloxybutadiene as starting materials.

A novel and highly functionalized crotofolane diterpene, crotofolin E ( 4 ), has been isolated from Croton corylifolius L. (Euphorbiaceae) and its stereostructure determined from spectral and X-ray crystall crystallographic analyses.

NMR evidence establishes that both diastereomers of 1,2-diphenyl-1,2-bis(4-pyridyl)ethane (2), identified by optical resolution of the racemic form, exist predominantly in the anti conformation. Furthermore, empirical force field calculations show that the gauche conformer of 1,1,2,2-tetrakis(2,6-dimethylphenyl)ethane (3) is less stable by ca. 10 kcal mol than the anti structure. It thus appears that neither polar effects nor steric congestion are effective in reversing the marked preference of 1,1,2,2-tetraphenylethane (1) and other unclamped tetraarylethanes for an anti ground state. In contrast, as predicted by empirical force field calculations and confirmed by X-ray and NMR evidence, the ground state structure of 9,9'-bifluorenyl (4) is gauche. The conformational behavior of 1–4 is discussed in terms of the intramolecular aryl ring stacking in clamped and unclamped tetraarylethanes.

The synthesis and X-ray structural determination of 3-O-[(bis-morpholino)phosphinyl]-5,6-O-isopropylidene- l -ascorbate (9) are described. Acid-catalyzed hydrolysis of 9 afforded the 2-O-phosphate 6. Definitive structural proof of 6 is based on a study of the pH profile of its UV spectra as compared with those of ascorbic esters, 2 and 9 (Figs. 1–3).

Synthesis of the ethyl ester 2a of the debromo-aglycone of surugatoxin 1 has been achieved in 10 steps starting from readily available ethyl 2-(2-oxo-3-indolenyl)-3-oxo-4-phthalimidobutyrate 3.

Antibioticum X-5108 ist ein Naturprodukt mit neuartiger Struktur. Behandlung des Antibioticums mit Essigsaure fuhrte zu einem kristallinen Abbauprodukt, das als 3(S)-Athyl-3, 3a, 5(S), 6, 7, 7 a(R)-hexahydro-3a(R), 7(R)-dihydroxy-6, 6-dimethyl-5-[1(cis), 3(trans)-pentadienyl]-2H-furo[3, 2-b]pyran-2-on (5) identifiziert wurde.

The S-configuration of the alkaloids cryptostylines I, II, and III was assigned on the basis of a single crystal X-ray analysis of unnatural cryptostyline II hydrobromide (5.HBr: orthorhombic, P212121 a = 10·162, b = 12·352, c = 16·456 A) and confirmed by application of the aromatic chirality method. Further evidence for the configurational assignment was provided by the CD spectra of the monophenolic derivatives of unnatural cryptostyline II (14).

Aus fermentierten Kulturen von streptomyces antibioticus wurden die Titelverbindung (I) als eins der Hauptprodukte und das neue Dihydroindolon (II) als ein Nebenprodukt isoliert.