Nucleic acid related compounds. 63. Synthesis of 5′-deoxy-5′-methyleneadenosine and related Wittig-extended nucleosides

Abstract

Treatment of the purified 5′-aldehyde (2a) (derived from 6-N-benzoyl-2′,3′-O-isopropylideneadenosine (1a)) with methylenetriphenylphosphorane and successive deprotection with ammonia and acid gave 9-(5,6-dideoxy-β-D-ribo-hex-5-enofuranosyl)adenine (5′-deoxy-5′-methyleneadenosine) (4). Oxidation of 1a or 2′,3′-O-isopropylideneadenosine (1b) and treatment of the crude 5′-aldehydes (2a or 2b) with (p-toluenesulfonylmethylene)triphenylphosphorane gave high yields of the 5′-deoxy-5′-tosylmethylene derivatives (5a or 5b). Removal of the tosyl group from 5b to give 3b was effected with tributylstannyllithium, but sulfone cleavage by the usual reductive methods failed. Reduction and deprotection of 5a or 5b gave 9-[5,6-dideoxy-6-(p-toluenesulfonyl)-β-D-ribo-hexofuranosyl]adenine (6b). Isomerization of the vinyl tosyl (5b) to a 4′,5′-unsaturated allylic tosyl derivative (7) occurred under cleavage conditions and in solutions of aqueous or organic bases. Key words: adenosine, 5′-deoxyadenosine, 5′-methylene-5′-deoxyadenosine, nucleosides.