Stereoselective Hydrogenation and Ozonolysis of Iridoids. Conversion into Carbocyclic Nucleoside Analogues

Stereoselective hydrogenation of the iridoids geniposide (9) and aucubin (19) was achieved by using the 1-methyl-1-methoxyethyl ether (MIP) as protecting group for the allylic alcohol, as it enhanced the stereoselectivity and prevented undesired hydrogenolysis. Ozonolysis of the hydrogenation product from 9, adoxoside (11), with reductive work-up, afforded either a chiral lactone (25) or a chiral polyol (26), depending on the reduction conditions. Polyol 26 was subjected to protecting group manipulation and subsequent oxidation and reductions to yield cyclopentane building blocks (29-34), which by Mitsunobu couplings with purines afforded carbocyclic nucleoside analogues (7, 8 and 35)