Purines. LVII.1) Regioselective Alkylation of N6,9-Disubstituted 8-Oxoadenines: Syntheses of the Sea Anemone Purine Caissarone and Some Positional Isomers and Analogues

Abstract

The first total synthesis of caissarone hydrochloride (1), a constituent of the sea anemone Bunodosoma caissarum, has been accomplished via a two-step route starting from (3), which is obtainable from 9-methyladenine (5) through a four-step route. The key step in the synthesis is the regioselective methylation of 3 at N(3), which has been designed on the basis of a methylation study of (11). Some positional isomers (19, 24, and 31) and analogues (8, 26, and 32) of 1 have also been synthesized. A spectroscopic study has suggested that the free base (23) of caissarone is capable of forming a hetero-base pair (such as 41) with 2‗,3‗,5‗-tri-0-acetylguanosine (40). © 1993, The Pharmaceutical Society of Japan. All rights reserved.