The effect of diethylamine on Stille alkylations with tetraalkylstannanes.

The addition of diethylamine to Stille alkylation reactions using stannanes improves yields by reducing beta-hydride elimination and reduction reactions, it also serves as a substitute for other additives such as Cu(I)I.

Metabolism of 3-(13)C-malate in primary cultures of mouse astrocytes.

Malate, specifically labeled with carbon 13 on C(3), was synthesized by chemical means and used to study malate metabolism by primary cultures of mouse cortical astrocytes. 3-(13)C-Malate in combination with glucose as well as 3-(13)C-malate alone were used as substrates; the effect of 3-nitropropionic acid, an inhibitor of succinate dehydrogenase and fumarase was also examined. The consumption of malate was only 0.26 micromol/mg of protein, approx. 25-fold lower than the consumption of glucose. Besides lactate, glutamine and fumarate were the two major metabolites released to the medium. Very low and similar levels of isotopic enrichment were detected on C(2) and C(3) of lactate; glutamine was labeled on C(2) and C(3) to a similar extent as well and labeling on C(4) was only detected when glucose was not added. These labeling studies suggest that cytosolic malic enzyme is not active in primary astrocytes and support the occurrence of pyruvate recycling in astrocytes.

The first synthesis of (-)-asperpentyn and efficient syntheses of (+)-harveynone, (+)-epiepoformin and (-)-theobroxide.

A generally applicable strategy for the synthesis of a range of polyoxygenated cyclohexane natural products has been developed. The enantioselective syntheses of (-)-theobroxide, a polyoxygenated cyclohexane natural compound with potent growth inducing properties in potato microtubers has been achieved via a 1,2 O-silyl migration between trans-hydroxyl groups and a remote hydroxyl directed epoxidation of an enone derived from quinic acid. A thus derived alpha-iodoenone was subjected to Stille coupling with tetramethylstannane to afford the first title compound. A similar strategy enabled a route to the complete asymmetric synthesis of the acetylenic phytotoxin (+)-harveynone. By selective reduction of (-)-theobroxide, (+)-epiepoformin was also prepared in enantiopure form and similarly, stereoselective reduction of (+)-harveynone completed the first enantioselective synthesis of (-)-asperpentyn, another natural compound with antimicrobial activity.

Preparation of sucrose heptaesters unsubstituted at the C-1 hydroxy group of the fructose moiety via selective O-desilylation.

Selective O-desilylation of 6,1',6'-tri-O-tert-butyldiphenylsilyl-2,3,4,3',4'-penta-O-benzo ylsucrose with hydrofluoric acid in acetonitrile led to the 1'-O-tert-butyldiphenylsilyl derivative (96% yield), which was further perbenzoylated and deprotected at OH-1' with tetrabutylammonium fluoride (86%). An analogous sequence with the corresponding O-acetylated sucrose derivative and tetrabutylammonium fluoride as desilylating agent resulted in a lower yield of the C-1' hydroxy derivative.