Structure elucidation of glycosidic antibiotics, glykenins, from Basidiomycetes sp. II. Absolute structures of unusual polyhydroxylated C26-fatty acids, aglycones of glykenins

The structures of three aglycones of glykenins, produced by Basidiomycetes sp., were determined to be (2S, 16R, 17S, 21R)-2, 16, 17, 21-, (2S, 17R, 18S, 22R)-2, 17, 18, 22-, and (2S, 17S, 18S, 22R)-2, 17, 18, 22-tetrahydroxyhexacosanoic acids (3a-c). The absolute configurations of two of the four hydroxy groups in 3a-c were established by chiral synthesis of the degradation products (6a-c and 7a-c). Chemical transformation of 3a-c to 6, 8-dioxabicyclo[3.2.1]octane derivatives (18-c) revealed the relative and absolute configurations of the acyclic 1, 2-diol moieties in 3a-c.