Hypoxia-inducible factor asparaginyl hydroxylase (FIH-1) catalyses hydroxylation at the β-carbon of asparagine-803

Asparagine-803 in the C-terminal transactivation domain of human hypoxia-inducible factor (HIF)-1 α-subunit is hydroxylated by factor inhibiting HIF-1 (FIH-1) under normoxic conditions causing abrogation of the HIF-1α/p300 interaction. NMR and other analyses of a hydroxylated HIF fragment produced in vitro demonstrate that hydroxylation occurs at the β-carbon of Asn-803 and imply production of the threo-isomer, in contrast with other known aspartic acid/asparagine hydroxylases that produce the erythro-isomer.

Stereoselectivity of directed epoxidations of 22-hydroxy-Δ23-sterol side chains

A series of 22-hydroxy-Δ23-sterols comprising (3β,5α,6β,22S)-6-methoxy-3,5-cyclo-25,26,27-trinorcholest-23-en-22-ol (6), (3β,5α,6β,22S,23E)-6-methoxy-3,5-cyclo-26,27-dinorcholest-23-en-22-ol (7), 3β,5α,6β,22R)-6-methoxy-23-methyl-3,5-cyclo-25,26,27-trinorcholest-23-en-22-ol(10),3β,5α,6β,22S,23Z)-6-methoxy-3,5-cyclo-26,27-dinorcholest-23-en-22-ol (11), and 3β,5α,6β,22R)-6-methoxy-3,5-cyclo-26,27-dinorergost-23-en-22-ol (12) were subjected to epoxidation with m-chloroperbenzoic acid and tert-butyl hydroperoxide in the presence of either vanadyl acetoacetonate or molybdenum hexacarbonyl, and the threo:erythro ratios of the products were determined. The results are of relevance for the synthesis of sterols with oxygenated side chains, such as brassinolide (1). The oxidations of 6 and 7 were erythro selective with all three oxidants, especially with the vanadium-catalyzed system. Peracid oxidation of the 22-tert-butyldimethylsilyl ether (8) and 22-pivaloate (9) of alcohol 7 showed similar erythro selectivity to that of the parent compound 7. Allylic alcohol 10 gave exclusively the erythro epoxide with all three oxidants, while 11 and 12 were threo-selective under all three conditions. Molecular modeling indicated that erythro selectivity in the vanadium-catalyzed epoxidation of 10 was consistent with a destabilizing interaction (A(1,2) strain) between the gem-methyl and C(21) methyl groups in the conformation required for formation of the threo-isomer. The threo-selective peracid oxidations of 11 and 12 were attributed to A(1,3) strain between the cis-methyl groups and C(20) in the conformation required for formation of the erythro-epoxide. The differences in the calculated energies of conformations leading to the threo- and erythro epoxide diastereomers of substrates containing no gem or cis substituents proved too small to permit reliable prediction of diastereoselectivity. Key words: 22-hydroxy-Δ23-sterols, brassinosteroids, allylic alcohols, epoxidation, diastereoselectivity

Vitamin K-dependent carboxylation. Mechanistic studies with 3-fluoroglutamate-containing substrates

The tripeptides t-butyloxycarbonyl-Xaa-Glu-[3H]Val, where Xaa is either (2R,3S)- or (2R,3R)-3-fluoroglutamate (respectively the erythro and the threo isomer), were synthesized and their behaviour during vitamin K-dependent carboxylation was studied. Neither peptide was carboxylated. The erythro compound gave rise to an HF-elimination product representing 1% of the starting material. This HF elimination did not occur during incubation of the threo compound. The formation of the dehydropeptide, probably by elimination of an F- anion from an intermediate carbanion, favours the ionic pathway for vitamin K-dependent carboxylation.

The Stereoisomers of 5-Bromo-6,8-dimethoxy-1,2,3-trimethyl-1,2,3,4-tetrahydroisoquinoline. X-Ray Crystal-Structure of the trans Isomer

Henry reaction between 3,5-dimethoxybenzaldehyde (2) and nitroethane gave (E)-2-(3,5-dimethoxyphenyl)-1-methyl-1-nitroethene (3). Under mild conditions the erythro and threo nitro aldols intermediate in this reaction could be isolated as their acetates. The threo isomer was obtained in diastereoisomeric excess. The nitrostyrene (3) was converted in several steps into cis-(20) and trans-5-bromo-6,8-dimethoxy-1,2,3-trimethyl-1,2,3,4-tetrahydroisoquinoline (18). The single-crystal X-ray structure of compound (18) is reported.

Reactions of Nitro Sugars. XXXI. Formation of 2,3- and 3,4-Unsaturated Derivatives in the 6-Deoxyhexose Series

The methyl 3,6-dideoxy-3-nitrohexopyranosides having the α-L-galacto (1), α-L-manno (2), α-L-galacto (3), and α-L-talo (4) configurations and their 2,4-diacetates (6, 11, 16, and 18, respectively) served as starting materials for the preparation of 2,3- and 3,4-unsaturated derivatives. The reactions employed included dehydroacetylation of diacetates and of some monoacetates (5, 7, and 12) that had been obtained by partial acetylation or partial acid-catalyzed de-O-acetylation, and also dehydrations occurring under conditions of acetylation. The following nitroolefins were obtained: methyl 3,4,6-trideoxy-3-nitro-α-L-erythro-hex-3-enopyranoside (8) and its 2-acetate (9), the corresponding α-L-threo isomer (13) and its 2-acetate (10) and 2-O-methyl derivative (20), and methyl 2,3,6-trideoxy-3-nitro-α-L-erythro-hex-2-enopyranoside (14) and its 4-acetate (15) as well as the 4-acetate (17) of the corresponding α-L-threo isomer. In addition, 1,4-di-O-acetyl-2,3,6-trideoxy-3-nitro-α-L-threo-hex-2-enose (19) was obtained by acetolysis of 17. Factors assumed to be responsible for a pronounced regioselectivity in some of the reactions are discussed.