XANTHINE-OXIDASE (XO) - RELATIVE CONFIGURATION OF COMPLEXES FORMED BYTHE ENZYME, 2-N-ALKYL-HYPOXANTHINE OR 8-N-ALKYL-HYPOXANTHINE AND 2-N-ALKYL-8-AZAHYPOXANTHINES .12.

Several 2- or 8-n-alkyl-hypoxanthines and a 2,8-di-n-pentyl-hypoxanthi ne were synthesized and tested as substrates or inhibitors of Xanthine Oxidase (XO). 8-Alkyl derivatives showed a substrate behaviour, where as 2-alkyl substituted compounds were non-substrates and inhibitors. 2 ,8-di-n-pentyl-hypoxanthine was ineffective as inhibitor. The comparis on between their activity allowed us to conclude that the complexes fo rmed by the enzyme and the cited n-alkylhypoxanthines or 2-n-alkyl-8-a zahypoxanthines involve their N(3) and N(9) positions in all the cases . The position of the n-alkyl chain determines the disposition of the molecule inside the complex: 2-n-alkyl-hypoxanthines and 2-n-alkyl-8-a zahypoxanthines gave complexes with the same orientation of heterocycl ic moieties, opposite that given by 8-n-alkyl-hypoxanthines.