PURINE NUCLEOSIDES .22. SYNTHESIS OF ANGUSTMYCIN A (DECOYININE) AND RELATED UNSATURATED NUCLEOSIDES

The antibiotic angustmycin A (decoyinine) (10) has been prepared in several steps from psicofuranine (la). The synthesis of 1 ′,3′,4′-O-orthoformylpsicofuranine (5) proved the β configuration of la and provided the required blocked derivative for the synthesis of 6′-O-p-toluenesulfonyl-1, ′3 ′,4′-O-orthoformylpsicofuranine (6). Compound 6 was treated with potassium t-butoxide to give 1′,3′,4′-O-orthoformyldecoyinine (7), which was deblocked to yield 6-amino-9-(6-deoxy-β-D-erythro-hex-5-enofuran-2-ulosyl)purine (10), identical with natural angustmycin A and decoyinine. The synthesis of 6-amino-9-(5-deoxy-β-D-erythro-pent-4-enofuranosyl)purine (8) was accomplished from adenosine 16 by a similar base-catalyzed treatment of 5′-O-p-toluenesulfonyl-2′,3′-O-ethoxymethylideneadenosine (3). Reaction of 6-amino-9-(2,3-O-isopropylidine-5-deoxy-O-D-erythro-pent-4-enofuranosyl)purine (13) with bromine provided the first reported N3Å4′-furanose cyclonucleoside, 14. Palladium-catalyzed hydrogenation of 13 proceeded stereospecifically to yield 6-amino-9-(5-deoxy-α-L-lyxo-pentofuranosyl)purine (15) after deblocking. A new synthesis of the 4′ epimer of 15, 5′-deoxyadenosine (20), was accomplished from adenosine. © 1968, American Chemical Society. All rights reserved.