Total Syntheses of (+)-Gabosine P, (+)-Gabosine Q, (+)-Gabosine E, (−)-Gabosine G, (−)-Gabosine I, (−)-Gabosine K, (+)-Streptol, and (−)-Uvamalol A by a Diversity-Oriented Approach Featuring Tunable Deprotection Manipulation
A new diversity-oriented approach to C7-cyclitols, which possess a broad spectrum of biological activities, is developed. The key polyoxygenated intermediates with different O-protecting groups were accessed by an intramolecular aldol-cyclization of a diketone derived from δ-d-gluconolactone. The versatile intermediates can be easily transformed into structurally different carbasugars based on control
and E (5), which share the same trihydroxycyclohexenone skeleton, were synthesized from enone 11 as the common intermediate. The key building block 11 was accessed by an intramolecular aldolcyclization of a diketone derived from D-glucose (8).
Short syntheses of Gabosines C (1) and E (3), startingfromD-ribose are reported. The syntheses employ an intramolecular nitrile oxide cycloaddition to generate the carba-sugar skeleton, and result in the first total syntheses of unnatural (+)-Gabosine C and natural (+)-Gabosine E.