Synthesis of a C29-C51 Subunit of Spongistatin 1 (Altohyrtin A) Starting from (R)-3-Benzyloxy-2-methylpropan-1-ol

A protected C29-C51 subunit ((+)-38) of Spongistatin 1 has been obtained. Key steps involve the aldol condensation of (3S,4R)-3-methyl-7-[(paramethoxybenzyl)oxy]-4-[(triethylsilyl)oxy]octan-2-one ((-)-6) with (tert-butyl)dimethylsilyl 4-deoxy-2,3-di-O-(methoxymethyl)-4-methyl-6-O-(tert-butyl)dimethylsilyl)--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 paramethoxybenzoate (16). Aldehyde (+)-7 was derived from (R)-3-benzyloxy-2-methylpropan-1-ol ((+)-10) in 13 formal steps but requiring the isolation of 5 intermediate products only. The longest linear synthetic scheme converts (+)-10 into (+)-38 in 2% overall yield (isolation of 11 intermediate products).