Emimycin

One hundred compounds were evaluated as ligands of Toxoplasma gondii uracil phosphoribosyltransferase (UPRTase, EC 2.4.2.9) by examining their ability to inhibit this enzyme in vitro. Inhibition was quantified by determining apparent Ki values for those compounds that inhibited T. gondii UPRTase by greater than 10% at a concentration of 2 mM. Five compounds (4-thiopyridine, 2-thiopyrimidine, trithiocyanuric acid, 1-deazauracil and 2,4-dithiouracil) bound to the enzyme better than two known substrates for T. gondii UPRTase, 5-fluorouracil and emimycin, which have antitoxoplasmal activity (Pfefferkorn ER, Exp Parasitol 44: 26-35, 1978; Pfefferkorn et al., Exp Parasitol 69: 129-139, 1989). In addition, several selected compounds were evaluated as substrates for T. gondii UPRTase, and it was found that 2,4-dithiouracil is also a substrate for this enzyme. On the basis of these data, a structure-activity relationship for the binding of ligands to T. gondii UPRTase was determined using uracil as a reference compound.

The characteristics of anticoccidial activities of 6-azauracil (AzU) were investigated in the battery trials utilizing the White Leghorn cockerels, which were infected with Eimeria tenella, E. necatrix, E. acervulina, E. maxima and/or E. brunetti. AzU was mixed into the basal starter feed and fed ad libitum to the birds from 1 day before the inoculation of oocysts to the time of necropsy. AzU showed remarkable anticoccidial activity against E. tenella and E. necatrix infections at doses of 1,000 ppm in feed or more, and fairly good effect against E. acervulina infection at the dose of 4,000 ppm in feed. Inadequate effect against E. maxima infection and null in effect against E. brunetti at the dose of 4,000 ppm were resulted for this drug. The effect of 6-azauridine, ribonucleoside of AzU against E. tenella and E. necatrix infections at 1,000 ppm was tested and revealed negative results. In the test with AzU-resistant line of E. tenella, cross resistance was confirmed between AzU and emimycin riboside, a uridine analogue. Activity of AzU was studied in vitro against E. tenella in chick kidney cells. AzU inhibited the development of the first- and second-generation schizonts at 100-200 ppm in the medium. Degenerated parasites were observed.

The synthesis of emimycin, 5-substituted emimycin analogues and the corresponding ribo- and 2'-deoxyribonucleoside derivatives is described. Emimycin, its 5-substituted congeners and the ribonucleoside derivatives are completely devoid of antiviral activity against RNA viruses. In contrast, some of the 2'-deoxyribosyl emimycin derivatives are potent inhibitors of the replication of herpes simplex virus-1 and varicella-zoster virus, lacking cytotoxicity.