Milbemycin A4

Epoxidation reactions (MCPBA epoxidation and Sharpless epoxidation) were examined as a means of chemically modifying milbemycins as part of our program for discovering anthelmintics. 8,9-Epoxy-, 14,15-epoxy-, 8,9-14,15-diepoxy-, and 3,4-8,9-14,15-triepoxymilbemycin A4 were selectively obtained from milbemycin A4 and its derivatives, in which either the C-5 and C-7 hydroxyl groups or C-5 alone were protected as appropriate by a silyl ether (in the former case) or a carbonyl group. Further silylation or epoxidation on these epoxidized compounds indicated that the configuration of each epoxide moiety of the mono- and diepoxides is in accord with that of the corresponding epoxide moiety of the triepoxide. Furthermore, in order to confirm the absolute configurations of these epoxide functionalities, an X-ray analysis of a carbamate derivative from the triepoxymilbemycin was conducted.

Introduction:Moxidectin is a milbemycin endectocide recently approved for the treatment of human onchocerciasis. Onchocerciasis, earmarked for elimination of transmission, is a filarial infection endemic in Africa, Yemen, and the Amazonian focus straddling Venezuela and Brazil. Concerns over whether the predominant treatment strategy (yearly mass drug administration (MDA) of ivermectin) is sufficient to achieve elimination in all endemic foci have refocussed attention upon alternative treatments. Moxidectin's stronger and longer microfilarial suppression compared to ivermectin in both phase II and III clinical trials indicates its potential as a novel powerful drug for onchocerciasis elimination.Areas covered:This work summarizes the chemistry and pharmacology of moxidectin, reviews the phase II and III clinical trials evidence on tolerability, safety, and efficacy of moxidectin versus ivermectin, and discusses the implications of moxidectin's current regulatory status.Expert opinion:Moxidectin's superior clinical performance has the potential to substantially reduce times to elimination compared to ivermectin. If donated, moxidectin could mitigate the additional programmatic costs of biannual ivermectin distribution because, unlike other alternatives, it can use the existing community-directed treatment infrastructure. A pediatric indication (for children <12 years) and determination of its usefulness in onchocerciasis-loiasis co-endemic areas will greatly help fulfill the potential of moxidectin for the treatment and elimination of onchocerciasis.

Azole resistance in Candida glabrata, a pathogenic yeast, has prompted studies of compounds that have therapeutic potential by reversing azole resistance. Milbemycin A4 oxime blocked azole efflux and enhanced azole susceptibility fourfold in 28 clinical isolates of C. glabrata. Specificity of the milbemycin A4 oxime effect depended on the drug transporter and the substrate being effluxed. The major effect of milbemycin A4 oxime was inhibition of azole and rhodamine 6G efflux by the ATP-binding cassette (ABC) transporters CgCDR1 and PDH1. Milbemycin A4 oxime effect did not extend to oligomycin, transported by the ABC transporter YOR1 or to benomyl, transported by the major facilitator superfamily transporter, CgFLR1. Milbemycin A4 oxime did not suppress transcription of CgCDR1 but increased CgCDR1 expression 126-fold. Selectivity of the effect is compatible with the concept that milbemycin A4 oxime may interact directly with one or more drug-binding sites of the major azole transporters.