Pteridines diuretic

For the much-used pteridine diuretic triamterene, 2,4,7-triamino-6-phenylpteridine, see Section 14. i. For further reading on the biochemistry of anti-folic agents, see Blakley (1969). 

Pteridines are also used as pharmaceuticals. Triamterene 15 is a diuretic that promotes excretion of Na" and retains K+. The folic acid antagonist methotrexate 16 (amethopterin) is of considerable importance as an antineoplastic agent in cancer chemotherapy. 

Pteridines have a marked potential for influencing biological processes. Early screening of pteridine derivatives revealed that 2,4-diamino-6,7-dimethylpteridine was a fairly potent diuretic. Further structural modification led to the development of triamterene. 

The systematic name for Dyrenium, a diuretic, is 2,4,7-triaminO 6-phenylpteridine. (a) Number the heterocyclic ring system. It is called pteridine. (b) Explain this choice of numbers. 

In contrast to hydrochlorothiazide and bumetanide, triamterene represents a potassium-sparing diuretic agent with a pteridine nucleus and no sulfonamide function. Its six-fold methylated derivative preferably eliminates a hydrogen radical from its molecular ion at m/z 337 to form the base peak at m/z 336 (Fig. 3.11c). Additionally, the loss of a methyl radical (-15 Da), which results in m/z 322, and the consecutive release of methyl methyleneamine (-43 Da) and a methyl residue, were suggested to form the fragments at m/z 294 and 279, respectively (Scheme 3.10c). ... 

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