Synthesis of (+)-(5S,6S)-Azafrin Methyl Ester; Absolute Configuration of Aeginetic Acid and of Further Vicinal Apocarotene-diols

Article abstract of DOI:10.1002/hlca.19820650137

We describe the synthesis of a series of optically active vicinal apo-β-carotene-diols.Thus, starting from (+)-(5S,6S)-5,6-dihydroxy-5,6-dihydro-β-ionone (2) we have prepared the (Z/E)-isomeric(+)-C15-esters 7 and 8, the (+)-retinoic derivatives 14, 15, 18, 19 and (+)-methyl azafrinate (22), the enantiomer of the naturally occuring compounds (s.Scheme 1).Our synthesis also establishes the absolute configuration of aeginetic acid (24), aeginetoside (25) and aeginetin (26), compounds isolated from the root parasite Aeginetia indica by Indian and Japanes workers (s.Scheme 2).The presented synthesis of optically active methyl azafrinate confirms our previous assignment of the absolute configuration of azafrin (1a), which was based on degradative evidence.