Summary
The chemical syntheses of 6,7-(α-pyridyl)-1-(2,3,5-tri-O-benzoy-β-D-ribofuranosyl)-lumazine (6) and the corresponding free nucleoside 7 are described. Thiation of 6 with P4S10 gave a salt type adduct derivative of 4-thiolumazine 8 which afforded the free nucleoside 9 on deblocking. Treatment of 8 with methanolic NH3 gave the isopterin-N-1 nucleoside 10. 2,2' -Anhydro compound 13 was obtained by the diphenyl carbonate technique and characterised as the diacetate 14. Acid hydrolysis of 14 gave the arabino-nucleoside 15. which was isolated also from hydrolysis of 14 with hydroxide ion. Reaction of 7 with acetyl bromide gave the 2'-bromo-2'-deoxy derivative 11 as minor product together with triacetate 12 as the main analogue. Reduction of the bromo function in 11 into the expected 2'-deoxy analogue during the treatment with tri-n-butyltin hydride has failed and the 2.2' -anhydro compound 15 was the only product isolated. Alternatively. the 6,7-bis-(α-pyridyl)-1-(2-deoxy-3.5-di-O-toloulyl-α and β-D-ribofuranosyl)-Iumazine (17) and (19) were synthesized from direct condensation of sugar 16 and the silylated base 4. Debolcking of 17 and 19 with sodium methoxide gave the free analogues 18 and 20 respectively.
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