Complex biohopanoids synthesis: efficient anchoring of ribosyl subunits onto a C(30) hopane

Bacteriohopanoids represent a particularly important series of triterpenoids, widely distributed in bacteria. One of the common features of these pentacyclic hopanepolyols is the presence of an extended non-terpenoid and polyhydroxylated side chain attached to the triterpenic moiety through a C--C bond. The biological function of biohopanoids also has to be addressed when one considers the broad diversity in both structures and functionalities found in the side chain. Moreover, the stereochemistries of some biohopanoids are still unconfirmed, due to the lack of synthetic methods to prepare them. In this study we describe an efficient methodology for the formation of the C--C bond between the C(30)-hopane component and C(5)-polyhydroxylated carbohydrates through the use of a hopanyllithium intermediate, which has enabled us to synthesize several biohopanoid derivatives. We also report the first synthesis of hopanepentol bearing an additional hydroxy group at position C31.