Synthesis of a C(29)-C(51) subunit of spongistatin 1 (Altohyrtin A) starting from (R)-3-benzyloxy-2-methylpropan-1-ol.

A protected C(29)-C(51) subunit ((+)-38) of spongistatin 1 has been obtained. Key steps involve the aldol condensation of (3S, 4R)-3-methyl-7-[(p-methoxybenzyl)oxy]-4-[(triethylsilyl)oxy]octan- 2-o ne ((-)-6) with (tert-butyl)dimethylsilyl 4-deoxy-2, 3-di-O-(methoxymethyl)-4-methyl-6-O-(tert-butyl)dimethylsilyl)-bet a-D -glycero-L-gluco-heptodialdo-1,5-pyranoside ((+)-7) and a C-glycosidation of (4R,7R&S,E)-7, 8-dichloro-2-methylidene-1-(trimethylsilyl)oct-5-en-4-yl p-methoxybenzoate (16). Aldehyde (+)-7 was derived from (R)-3-benzyloxy-2-methylpropan-1-ol ((+)-10) in 13 formal steps but requiring the isolation of five intermediate products only. The longest linear synthetic scheme converts (+)-10 into (+)-38 in 2% overall yield (isolation of 11 intermediate products).