Structural variations of N-acetylneuraminic acid, part 19: Synthesis of both epimeric pairs of the 4-C-methyl- and 4-deoxy-4-C-methyl- as well as of the ?-methylketoside of 4-deoxy-4-C-methylene-N-acetylneuraminic acid
作者:Michael Hartmann、Rudolf Christian、Erich Zbiral
DOI:10.1007/bf00815172
日期:——
While the reaction of the 4-oxo-Neu 5 Ac derivative 2a with tributoxy methyl zirconate led exclusively to equatorial 4-C-methyl derivative 3a, the analogous reaction with tetramethyl zirconate yielded a 3:2 mixture of both diastereoisomers 3a and 4a. After removal of protecting groups the 5-acetamido-3,4-dideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosoic acid 5a and 5-acetamido-3,4-dideoxy-4-C-methyl-D-glycero-D-talo-2-nonulosonic acid 6 a were obtained. The 4-C-methylene derivative was prepared by treatment of the same 4-oxo-derivative with CH2I2/Zn/Cp2ZrCl2. Subsequent hydrogenation led to both epimeric 4-deoxy-4-C-methyl derivatives 8a and 9a. Final removal of protecting groups gave the 5-acetamido-3,4,5-trideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosonic acid 10a respectively the 5-acetamido-2,7-anhydro-4-C-methyl-3,4,5-trideoxy-D-glycero-D-talo-2-nonulosonic acid 11a. The beta-methylketosides of the 4-deoxy-4-C-methyl- (16) and 4-C-methylene-Neu 5 Ac (15) were prepared via the peracetylated derivatives to obtain modell substrates for enzymatic studies. Thus all free acids were tested for inhibition of CMP-sialate synthase. Only the 4-C-methylene compound 15 showed most unexpectedly a strong competitive inhibition of this enzyme.