No abstract

No abstract

No abstract

The utility of the vitamin C and isovitamin C derived dibromo diacetates 3a,b for preparing synthetically useful chirons is further examined. Methodologies for transforming the readily accessible compounds 3a,b into 3,6-and 5,6-anhydrohexono-l,4-lactones lOa,b and 6a,b are presented. Elaboration of the lactone epoxides 6a-c has provided optically pure (S,S)-, meso-, and (R,R)-4,4'-bis-y-butyrolactones 18a-c. The difference in reactivity between some isomeric intermediates was related to the spatial arrangement a t the reactive sites. IntroductionUnequivocal stereocontrol constitutes the center piece of modern natural product synthesis. Most frequently the absolute configuration of the desired product has stemmed from the judiciously timed incorporation of chirally defined building blocks (chirons) during the synthesis and the subsequent configurational control of the asymmetric centers introduced. Carbohydrate-based schemes leading to a host of chirons have been especially rewarding in this respect; most of the desired routes have relied on the restructuring of furanoside and pyranoside systems.Our recent studies have demonstrated some relevant advantages of utilizing aldono-1,4-lactones, rather than the corresponding lactols, towards these ends. In practice aldono-1,4-lactones are highly crystalline, easily manipulated, and readily characterized substances. Large amounts of starting lactones may be prepared from inexpensive, commercially available materials. Publications from these laboratories have described the production of chirally defined butenolides 2 a -k '~~ from the ascorbic acids la,b and from ~-ribono-1,4-lactone. The preparation of three enantiomerically pure 4,5,6-trihydroxy-nor-~-leucines from la,b has also been r e p~r t e d .~

No abstract

Mineral phosphate (apatite) is activated for the synthesis of nucleotides when dilute solutions containing nucleoside and ammonium oxalate are evaporated in its presence. A natural, igneous fluorapatite was found to be even more effective in nucleotide synthesis than the more soluble hydroxylapatite. The phosphorylation is considerably more efficient if urea of cyanamide is also present. Hydrolysis of solutions of cyanogen to form oxalate and urea among other products is a spontaneous process that provides a geologically plausible model for necleotide synthesis on the primitive earth.

No abstract

1. Cell-free extracts of Penicillium charlesii G. Smith were used in a study of the biosynthesis of the galactofuranose polymer, galactocarolose. 2. UDP-glucose and UDP-galactopyranose were precursors of galactocarolose and it was shown that the galactofuranose residues in the polymer were formed from glucose without fission of the hexose carbon chain. 3. A new nucleotide, UDP-alpha-d-galactofuranose, was formed by the system and was a major product when polymer synthesis was inhibited by F(-) or Zn(2+); the nucleotide was isolated and its structure determined. 4. UDP-alpha-d-galactofuranose was efficiently utilized for polymer synthesis and shown to be formed from the pyranose nucleotides. 5. A route for the biosynthesis of galactocarolose, involving a novel ring contraction of the hexose residue while still attached to the nucleotide, is proposed.