POTENT INHIBITORS OF HUMAN INOSINE MONOPHOSPHATE DEHYDROGENASE TYPE-II - FLUORINE-SUBSTITUTED ANALOGS OF THIAZOLE-4-CARBOXAMIDE ADENINE-DINUCLEOTIDE

Three analogues of thiazole-4-carboxamide adenine dinucleotide (TAD) ( 1-3) containing a fluorine atom at the C2' of the adenine nucleoside ( in the ribo and arabine configuration) and at the C3' (in the ribo con figuration) were synthesized in high yield from the corresponding 5'-m onophosphates of 2'-deoxy-2'-fluoroadenosine (9), -(2-deoxy-2-fluoro-b eta-D-arabinofuranosyl)adenine (17), and 3'-deoxy-3'-fluoroadenosine ( 14), respectively. Pure 2',3'-0-isopropylidene-tiazofurin 5'-phosphori midazolide (8) was obtained by phosphorylation of the protected tiazof urin followed by treatment with carbonyldiimidazole and HPLC purificat ion. Reaction of 8 with 9 in DMF-d(7) (monitored by H-1 and P-31 NMR) afforded the desired dinucleotide 12, which after deisopropylidenation gave 1 in 82% yield. Small amounts of symmetrical dinucleotides AppA (10, 7.2%) and TRppTR (11, 8.0%) were also isolated during HPLC purifi cation of the major product 12. In a similar manner, compounds 2 and 3 were obtained by coupling of 8 with 14 and 17 in 80% and 76% yield, r espectively. All newly prepared fluoro-substituted compounds as well a s beta-CF2-TAD, earlier synthesized by us, showed good inhibitory acti vity against inosine monophosphate dehydrogenase type II, the isozyme which is predominant in neoplastic cells. Binding of 1 (K-is = 0.5 mu M), 2 (K-is = 0.7 mu M), and 3 (K-is = 2.9 mu M) was comparable to tha t of TAD (K-i = 0.2 mu M). The difluoromethylene bisphosphonate analog ue, beta-CF2-TAD (K-i = 0.17 mu M), was found to be equally effective as the best cofactor-type inhibitor, beta-CH2-TAD (K-i = 0.11 mu M). I nterestingly, the level of inhibition of horse liver alcohol dehydroge nase by these compounds was found to be much lower (0.1 mM for 1 and 2 and no inhibition up to 10 mM for 3). These findings show that inhibi tion of tumor-induced inosine monophosphate dehydrogenase type II is s elective and may be of therapeutic interest.