Lumazine and

Table 5 Physical Data for 8-Substituted Lumazines and Pterins...

AT-Oxidation is very sensitive to steric effects, since 1-substituted lumazines and pterins give only 5-oxides and the presence of bulky substituents at position 7 also directs oxidation to N-5. The pteridine 5-oxide (52) and 8-oxide (53) and the 5,8-dioxide (55) contain the AT-oxide groups as such, even when the possibility of AT-hydroxy tautomers exists, as in (53) i(54). 

Direct sulfurizations of simple monooxopteridines have not been successful, but the more stable lumazines and 2-thiolumazines are good substrates for P4S10 treatment, leading... 

Various 6- and 7-methyl- and 6,7-dimethyl-pteridines bearing either oxo or amino groups in the 2- and 4-positions can be oxidized to the corresponding carboxylic acids by alkaline potassium permanganate on heating. Various lumazine and pterin mono- and di-carboxylic acids have been prepared in this way (48JA3026, 78CB3790). 

The a-ionization of 7-methylpteridines can also be utilized in aldol-type condensation reactions. 7-Methyl-pterin and -lumazine and 2,4-diaminopteridine condense readily in aqueous base with aromatic aldehydes to afford 7-alkylidenepteridines (77JOC2951). A Claisen condensation requires the protection of the acidic hydrogens of the amide bonds. 

Pteridines can also function as catalysts in photooxidations whereby the protonated species of lumazine and aminopterin, respectively, catalyze the substrate-selective photooxidation of benzyl alcohol derivatives by oxygen in the presence of perchloric acid in acetonitrile <89CC816>. 

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