6-Substituted pterins, regioselective synthesis

The condensation of 2,5,6-triaminopyrimidin-4-one (76) vith unsymmetrical dicarbonyl compounds 77 led to the substituted pterins, vith preferential formation of the un vanted 7-isomer rather than the 6-isomer. A one-pot synthesis of 6-methylpterin 78 involved condensation vith methylglyoxal (77) at a controlled temperature (0-5 °C). Sodium bisulfate vas used to mask the more reactive aldehyde function. Under the action of micro vave irradiation, however, the 6-isomer can be obtained with total regioselectivity without addition of sodium bisulfate or hydrazine hydrate (Scheme 5.22) [66]. 

A regioselective synthesis of 6-substituted pterins 729, 730, and 731 was achieved using an MW-assisted direct Isay-type condensation of triamine 728 with methyl-glyoxal or aldohexoses to give under MWI, without addition of sodium bisulfate or hydrazine hydrate, 729 in 70% yield within 62 s and the sugar derivatives 730 and 731 in 40% and 38% yields, respectively, within 270 s (Scheme 141) (02TL8371). 

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