ABSTRACT

Figure 10. 1 Structure s o f som e naturall y occurrin g purin e an d pyr imidin e base s an d their structura l paren t compounds , purin e an d pyrimidine .

Caffeine Theophyllin e Theobromin e (1,3,7-trimethylxanthine) (1,3-dimethylxanthine ) (3,7-dimethylxanthine )

O O H II H I

I I I | ( ) | V O H ° = C ^ C W H O - C ^ C ^ /

H H H

Uric aci d Uri c aci d (lactam or keto form) (lacti m or enol form)

Figure 10.2 Tautomeri c forms of uric acid. Al though uri c acid does not occu r in nucleic acids (i t i s a degradatio n produc t o f adenin e an d guanine) , th e tautomeri c structure s observed her e ar e typica l o f al l purin e base s o f thi s type . A t p H 7 , th e ket o form s predominate.