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Communication | Special issue | Vol 7, No. 1, 1977, pp.205-216
Published online, 1st January, 1970
DOI: 10.3987/S-1977-01-0205
Pteridine Studies (IV). On the Mechanism of the Conversion of 2-(Methylthio)-4,6,7-triphenylpteridine into 2-Amino-4,6,7-triphenylpteridine and 6,8-Diphenyl-1-2-(methylthio)purine

Joek Nagel and Henk C. van der Plas*

*Laboratory of Organic Chemistry, Agricultural University, De Dreijen 5, 6703 BC Wageningen, The Netherlands

Abstract

The ring contraction of 2-(methylthio)-4,6,7-triphenylpteridine (3) into 2-(methylthio)-6,8-diphenylpurine (5a) by KNH2 in NH3 at -33° has been studied using selectively deuterium labelled pteridines. It was found that the purine obtained from 2-(methylthio)-4,6-diphenyl-7-(pentadeuterophenyl)pteridine — prepared by phenylation of 2-(methylthio)-4,6-diphenylpteridine with pentadeuterophenyllithium — only contained 13% of the deuterium label, indicating that C-7 is mainly expelled during the ring contraction. The mechanism is discussed. Furthermore the amination of 3 was studied using bath 15N-3 labelled compounds as well as K15NH2 in 15NH3. It was found that the amination of 3 takes place for 50-85% — depending on [KNH2] — according to a ring opening-ring closure mechanism (SN(ANRORC)) forming 2-amino-4,6,7-triphenylpteridine (4). Thus in 3 the pteridine nucleus is found to be attacked by the amide ion on C-4, C-2, C-6 and C-7 in the approximate order of reactivity: C-4 > C-2 > C-7 > C-6.