An improved synthesis of a key intermediate for (+)-biotin from d-mannose

An efficient and reproducible process for the synthesis of methyl 2,3,4,5-tetradeoxy-7,8-O-isopropylidene-d-arabino-nanonate (2), a key intermediate in the total synthesis of (+)-biotin (1), starting from readily available d-mannose is described. The crucial part of this synthesis was the development of a practical route to a novel O-benzyl protected unsaturated ester methyl (benzyl 5,6,7,8-tetradeoxy-2,3-O-isopropylidene-α-d-lyxo-nona-5,7-dienofuranosid) uronate (7), allowing the one-step preparation of hydroxy ester methyl 5,6,7,8-tetradeoxy-2,3-O-isopropylidene-α-d-lyxo-nanofuranuronate (8) by the catalytic debenzylation and hydrogenation over palladium on carbon catalyst. This procedure requires no chromatographic purification, which makes it ideal for synthetic preparation on an industrial scale.