Synthesis of Novel Conformationally Locked Carbocyclic Nucleosides Derived from 3-(Hydroxymethyl)bicyclo[2.2.1]heptane-2,5-diol

Abstract

(1R*,2R*,3R*,4R*,5R*,6S*)-3-Amino-5-(benzyloxy)-6-(hydroxymethyl)bicyclo[2.2.1]heptan-2-ol (18) was prepared in seven easy steps from benzyl (1R*,2S*,3S*,4S*)-3-(benzyloxy)bicyclo[2.2.1]hept-5-ene-2-carboxylate (10). Reaction of amine18with ethylN-((2E)-3-ethoxymethacryloyl)carbamate afforded 1-[(1R*,2R*,3R*,4R*,5S*,6R*)-6-(benzyloxy)-3-hydroxy-5- (hydroxymethyl)bicyclo[2.2.1]heptan-2-yl]-5-methylpyrimidine-2,4(1H,3H)-dione (21) and after deprotection by transfer hydrogenation, free thymine analogue22. The thymine derivative21was converted to 2,3'-anhydronucleoside26. Treatment of the benzyl derivative18with sodium in liquid ammonia led to amine19, which was used as key intermediate for the construction of (1R*,2R*,3R*,4R*,5R*,6S*)-3-(6-chloro-9H-purin-9-yl)-6-(hydroxymethyl)-bicyclo[2.2.1]heptane-2,5-diol (28) and (1R*,2R*,3R*,4R*,5R*,6S*)-3-(2-amino-6-chloro-9H-purin-9-yl)-6-(hydroxymethyl)bicyclo[2.2.1]heptane-2,5-diol (33). Ammonolysis of28led to 6-amino-9H-purine derivative29. 6-(Dimethylamino)-9H-purine analogue30and 6-(cyclopropylamino)-9H-purine analogues31and34were prepared by aminolysis of corresponding chloropurine derivatives.