1.5- Dimethyl-4-mercapto-imidazol

Of the 4-mercaptohistidine derivatives to which belong the ovothioles from the eggs of marine echi-noderms and mollusces, l,5-dimethyl-4-mercapto-imidazole due to the unusual stability of its thiyl radical is superior to glutathione as a one-electron donor (Holler and Hopkins 1990). Danen and Newkirk (1976) have similarly rationalised the remarkable stability of thionitroxide radicals. 

Knoth et al. [48] studied the electrochemical behavior of omeprazole with the aid of the direct-current and differential-pulse polarography. Omeprazole was determined in Britton-Robinson buffers pH 7-9 up to a concentration of 10 5 M. The mechanism of the reduction process on the dropping mercury electrode is elucidated. With the consumption of two electrons and two protons, omeprazole will be reduced to 5-methoxy-2-[(3,5-dimethyl-4-methoxypyridin-2-yl)methylthio]-lH-benzimidazole which will be cleaved with the uptake of two further electrons and two protons into 4-methoxy-2,3,5-trimethyl pyridine and 2-mercapto-5-methoxybenz imidazole. 

Imidazol l,4-Dimethyl-2-mercapto-tetrahydro- IV/ld, 252 Pyrazolidin l,2-Dimethyl-4-... 

H-Purin 1-Ethyl-2,7-dimethyl-8-mercapto-6-oxo-1,6-dihydro-E9b/2, 377 [5-COOR-4-(NH-Ac) —1-R —2-SH —imidazol 4-R-NH2]... 

Butan 3,3-Dimethyl-l-nitro-l-(2-pyridylthio)- E19a, 1264 [CO-O-N + En (rad.)] Cyclopropenthion Dimorpholino-E17d. 3001 (NR2 -> Thiono) Imidazol 1 -Cyclohexyl-2-mercapto-5-methoxycarbonyl- E8c, 43 [OHC —N(C6Hj, )-CH2 — COOR/HCOOR/R-ONa + KS-CN]... 

An example of application of this reaction employing NH OAc as a source of ammonia is depicted in Scheme 12.3. It is a key step in the preparation of a pyrimidine-imidazole-based library, where their biological activities were under study [7-9]. Thus, using glyoxal dimethyl acetal 11, ammonium acetate, and the required asymmetrical 1,2-diketone 10, prepared from 4-fluorobenzoate 9 and 2-mercapto-4-methylpyrimidine 8, the key intermediate 12 was obtained in good yield (86%). 

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