The structure and stereochemistry of gabosine K: Syntheses of 7-O-acetylstreptol and 7-O-acetyl-1-epi-streptol

Gabosine K, whose structure was erroneously assigned previously as 7-O-acetyl-4-epi-streptol, has been synthesized for the first time from D-glucose via a key carbocyclization strategy, intramolecular direct aldol reaction of a 2,6-diketone, in 15 steps with 13.5% overall yield. In the same manner, (+)-7-O-acetyl-streptol has been constructed for NMR spectral comparison. The structure, relative and absolute configurations of (-)-gabosine K are now revised and established as (-)-7-O-acetyl-1-epi-streptol, that is, (1R,2S,3S,4R)-tetrahydroxy-5-acetoxymethy lcyclohex-5-ene. Since the specific rotation of the natural product is not available, the absolute configuration of natural gabosine K is either (-)-7-O-acetyl-1-epi-streptol or its enantiomer.