-Carbonyl Substituted Glutathione Conjugates as Inhibitors of O. Volvulus GST2 Peter M. Brophy, a Alison M. Campbell, a Annamaria J. van Eldik, b Paul H. Teesdale-Spittle, b, * Eva Liebau c and Meng F. Wang b a Institute of Biological Sciences, University of Wales, Aberystwyth, Ceredigion SY23 3DA, UK b Department of Chemistry, De Montfort University, The Gateway, Leicester LE1 9BH, UK c Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Str 74, Hamburg, Germany Received 16 November 1999; accepted 28 February 2000 AbstractÐA series of b-carbonyl substituted glutathione conjugates were prepared and evaluated as inhibitors of OvGST2. Their speci®city for the parasite derived protein was assessed through comparison with their inhibition of human pGST. Inhibition of OvGST2 has been demonstrated at low micromolar concentrations for these conjugates and selectivity for OvGST2 over human p- GST of greater than 10-fold has been achieved. # 2000 Elsevier Science Ltd. All rights reserved. Introduction The ®larial nematode parasite Onchocerca volvulus causes onchocerciasis; a major cause of preventable blindness and severe dermatitis in Africa. Glutathione S-transferases (GSTs) are the linchpin of parasitic helminth defence mechanisms, providing their major phase II detoxi®ca- tion system and accounting for up to 4% of the total soluble protein. Two O. volvulus GSTs have been repor- ted to date, OvGST1 and OvGST2. We have previously reported the isolation of puri®ed active recombinant OvGST2. 1 GSTs detoxify electrophilic compounds, 2 including many anthelmintics and cytotoxins arising from the eector mechanism of the immune response, 3 through catalysis of their conjugation to glutathione. Unlike mammalian GSTs, parasitic nematode GSTs are not well characterised. Biochemical, immunological and primary amino acid sequence analysis fails to place OvGST2 into any of the ®ve characterised mammalian species independent soluble GST families (a, m, p, y and s). Homology models indicate critical structural dier- ences at the active site between host and parasite enzymes. In particular, the parasitic enzymes, whilst strongly topologically related to the mammalian p-GST family, have a very open hydrophobic binding cleft. 4 This is in contrast to that found in the mammalian enzymes, which have a more constricted feature. By contract, the glutathione binding site is closely related to that found in the mammalian enzymes: Notably the Tyr 115 residue is almost identically placed in both the mam- malian and parasite enzymes. This residue is a potential target for binding of a number of p-GST inhibitors, all bearing a carbonyl moiety b to the point of where glu- tathione conjugation occurs. 5,6 Given the signi®cant divergence from host GSTs, we propose that selective inhibition of parasite derived GST enzymes is a realisable chemotherapeutic target. This should ultimately tip the molecular balance in favour of the host during the characteristically chronic nematode infection and may be an important adjunct in eective immuno- and chemotherapy. 3 Selective inhibi- tors of nematode GST will also provide new tools to study host±parasite interactions. It is our hypothesis that suitable derivatisation of b-keto substituted glutathione S-conjugates will engender speci- ®city along with established abolition of target enzyme activity. As part of our ongoing investigations into the utility of GSTs as a target for antiparasitic agents, we have synthesised a series of b-carbonyl substituted glutathione conjugates as inhibitors of OvGST2. Chemistry Enones were synthesized by the base catalysed Aldol con- densation and the a,b -unsaturated esters were synthesized 0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(00)00142-6 Bioorganic & Medicinal Chemistry Letters 10 (2000) 979±981 *Corresponding author. Tel.: +44-116-257-7115; fax: +44-116-257- 7135; e-mail: molgraph@dmu.ac.uk