PARTIAL SYNTHESIS OF 6-BETA-EUDESMANOLIDES AND 6-BETA-GUAIANOLIDES FROM 6-ALPHA-EUDESMANOLIDES - SYNTHESIS OF ANALOGS OF ARTEPAULIN, COLARTIN AND TANNUNOLIDE-D

Epimerization at C-6 of polyfunctionalized 6 alpha-eudesmanolides was achieved by chemical means, to obtain 6 beta-eudesmanolides and after rearrangement, 6 beta-guaianolides. The epimerization process consists of the LiAlH4 reduction of a 6 alpha-lactone, selective protection of the hydroxymethylene group at C-12, oxidation and reduction at C-6 to epimerize this carbon, deprotection at C-12 and finally, lactonization with tetrapropylammonium perruthenate (TPAP) and 4-methylmorpholine N-oxide (NMO) in yields over 80%. The rearrangement of 1 beta-hydroxy-6 beta-colartin allow us to obtain 2,3-dihydro-6 beta-tannunolide D.