John F. Blount

New diterpene isocyanides from a sponge

Abstract 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.

Structural determination of ascorbic acid 2-o-phosphate formed via acid hydrolysis of an ascorbic acid 3-O-phosphinate

Abstract 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).

Structural studies of hydroxycitrates and their relevance to certain enzymatic mechanisms.

Abstract 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.

On the stereochemistry of photoaddition between α,β-unsaturated ketones and olefins. III.

The α,β-unsaturated ketone 1 yields with allene the photocycloadduct 3 predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence 1 → 4 → 5 → 6 → 7. The isomeric ketone 2 is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked.

A simple route to metalla-2-indane-1,3-diones

Abstract 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.

Conformational analysis of 1,1,2,2-tetraaryl-disilanes

Abstract 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.

The structure of cleomeolide, an unusual bicyclic diterpene from cleome viscosa L. (capparaceae)

Abstract 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

New 5-methylcoumarins from Ethulia conyzoides

Abstract 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 stereocontrolled route to a synthon for the aglycone of the aureolic acids

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

Absolute configuration of cryptostylines I, II, and III by x-ray analysis and aromatic chirality method

Abstract 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).