title: Replacement of isobutyl by trifluoromethyl in pepstatin A selectively affects inhibition of aspartic proteinases.
abstract: Two bis-trifluoromethyl pepstatin A analogues, carboxylic acid 1 and its methyl ester 2, have been synthesised in order to probe the properties and size of the trifluoromethyl (Tfm) group and compare it to the "bigger" isobutyl that is present in pepstatin A. The results demonstrate that Tfm can effectively replace the isobutyl chain as far as inhibitory activity against plasmepsin II (PM II), an aspartic proteinase from Plasmodium falciparum, is concerned. On the other hand, replacement of isobutyl by Tfm selectively affected activity against other aspartic proteinases tested. Two lines of evidence led to these conclusions. Firstly, compounds 1 and 2 retained single-digit nanomolar inhibitory activity against PM II, but were markedly less active against PM IV, cathepsin D and cathepsin E. Secondly, the X-ray crystal structures of the three complexes of PM II with 1, 2 and pepstatin A were obtained at 2.8, 2.4 and 1.7 A resolution, respectively. High overall similarity among the three complexes indicated that the central Tfm was well accommodated in the lipophilic S1 pocket of PM II, where it was involved in tight hydrophobic contacts. The interaction of PM II with Phe111 appeared to be crucial. Comparison of the crystal structures presented here, with X-ray structures or structural models of PM IV and cathepsin D, allowed an interpretation of the inhibition profiles of pepstatin A and its Tfm variants against these three enzymes. Interactions of the P1 side chain with amino acids that point into the S1 pocket appear to be critical for inhibitory activity. In summary, Tfm can be used to replace an isobutyl group and can affect the selectivity profile of a compound. These findings have implications for the design of novel bioactive molecules and synthetic mimics of natural compounds.
authors.affiliation: Actelion Pharmaceuticals Ltd. Gewerbestrasse 16, 4123 Allschwil, Switzerland. christoph.binkert@actelion.com
authors.forename: Christoph
authors.initials: C
authors.lastname: Binkert
authors.forename: Massimo
authors.initials: M
authors.lastname: Frigerio
authors.forename: Andrew
authors.initials: A
authors.lastname: Jones
authors.forename: Solange
authors.initials: S
authors.lastname: Meyer
authors.forename: Cristina
authors.initials: C
authors.lastname: Pesenti
authors.forename: Lars
authors.initials: L
authors.lastname: Prade
authors.forename: Fiorenza
authors.initials: F
authors.lastname: Viani
authors.forename: Matteo
authors.initials: M
authors.lastname: Zanda
mesh_terms: D000818:Animals; D000977:Antiparasitic Agents / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000737:chemistry; D049109:Cell Proliferation / Q000187:drug effects; D018360:Crystallography, X-Ray; D004353:Drug Evaluation, Preclinical; D006801:Humans; D066298:In Vitro Techniques; D008958:Models, Molecular; D008968:Molecular Conformation; D010436:Pepstatins / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D010963:Plasmodium falciparum / Q000187:drug effects / Q000201:enzymology; D011480:Protease Inhibitors / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D000977:Antiparasitic Agents; D010436:Pepstatins; D011480:Protease Inhibitors; D016282:Aspartic Acid Endopeptidases; D002402:Cathepsin D; C031375:pepstatin