Search

One route to the design of lead compounds for rational drug design approaches to developing drugs against trypanosomiasis, Chagas' disease and leishmaniasis is to develop novel inhibitors of the parasite-specific enzyme trypanothione reductase. A lead inhibitor based on a peptoid structure was designed in the present study based on the known strong competitive inhibition of trypanothione reductase by N-benzoyl-Leu-Arg-Arg-beta-naphthylamide and N-benzyloxycarbonyl-Ala-Arg-Arg-4-methoxy- beta-naphthylamide. In the target peptoid the arginyl residues were replaced by alkylimidazolium units and the benzyloxycarbonyl group by the benzylaminocarbonyl function. The peptoid was synthesised using t-butoxycarbonyl protection chemistry and couplings were activated by 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate. The resulting peptoid was shown to be a competitive inhibitor of recombinant trypanothione reductase from Trypanosoma cruzi with a K(i) value of 179 microM and with only weak inhibition of human erythrocyte glutathione reductase (the inhibition of glutathione reductase was at least 291-fold weaker than of trypanothione reductase).

Improved rationally designed lead drug structures against African trypanosomiasis, Chagas disease, and leishmaniasis were obtained against trypanothione reductase from Trypanosoma cruzi. Substituted-benzyl [3-(2-chloro-4a,10a-dihydrophenothiazin-10-yl)propyl]dimethylammonium salts, synthesized by Menschutkin quaternization of the tertiary alkylamine ω-nitrogen atom of chlorpromazine, were linear, competitive inhibitors of recombinant trypanothione reductase from T. cruzi, with either trypanothione disulfide or N-benzyloxycarbonyl-l-cysteinylglycyl 3-dimethylaminopropylamide disulfide as substrate. The permanent positive charge on the distal nitrogen atom of the tricyclic side chain contribution to binding was estimated as ≥5.6 kcal·mol-1 by comparison with the analogue with the cationic nitrogen atom of the quaternary replaced by an ether oxygen atom. A further major contribution to improving Ki values and inhibition strength was the hydrophobic natures and structures of the N-benzyl substituents. The str...

Synthetic protocols are presented both for D-PheSar and the corresponding cyclised diketopiperazine, prepared from N-t-butoxycarbonylprotected D-PheSar. Deprotection conditions could be manipulated to yield either D-Phenylalanylsarcosine or (R)-1-methyl-3-(phenylmethyl)-2,5-piperazinedione. Molecular modelling revealed several low energy conformers which contained a Z-peptide bond and which were readily amenable to cyclisation. Cyclisation was found by HPLC to be fastest in strongly acidic conditions.

A new method of preparation of optically active 13-S-hydroxyoctadecadienoic acid (13-HODE) is described. The key chemical step involves the coupling of methyl Z-10-iododec-9-enoate and tri-n-butyl(3(S)-dimethyl-tert-butylsilyloxy)-oct-l-enylstannane using a palladium (II) catalyst. The stannane is readily prepared from 3(S)-oct-l-yn-3-ol and various methods of producing this optically active material are described. In particular the enantioselective hydrolysis of (±)-3-acyloxyoct-l-ynes using an isolated enzyme is reported and this work is compared with results obtained using a whole cell system. Using the lipase from Mucor miehei a small advantage (in terms of the rate of the hydrolysis and the enantioselectivity of the process) is gained by using a chloroalkanoate instead of the corresponding ester possessing an isosteric methyl group in place of the halogen atom. However the best method for kinetic resolution of a racemic 3-acyloxyoct-l-yne involves the use of bakers' yeast (Glanzer, 1987). The new syn...

meso -2,6-Diaminopimelic acid, an important linking component of bacterial cell walls and a biosynthetic precursor of l -lysine has been prepared differentially protected in a stereospecific manner from both l -aspartic and l -glutamic acid. The key step to establish the second chiral center involves the asymmetric reduction of a pyruvate moiety with Alpine-Borane®. S -2-Amino-6-oxopimelic acid, the hydrolyzed open chain form of tetrahydrodipicolinic acid, a biosynthetic precursor of meso -2,6-diaminopimelic acid, was also prepared via deprotection of the key pyruvate intermediate.

By introducing cationic charge sites novel peptide lead inhibitor structures for trypanothione reductase have been designed using molecular modelling methods. The inhibitors showed reversible, linear competitive inhibition and the strongest peptide inhibitor to date was found to be N-benzyloxycarbonyl-Ala-Arg-Arg-4-methoxy-beta-naphthylamide with a Ki value of 2.4 microM and a selectivity for parasitic enzyme (trypanothione reductase) over the host enzyme (human glutathione reductase) of over 3 orders of magnitude.

Pyrimethamine acts by selectively inhibiting malarial dihydrofolate reductase-thymidylate synthase (DHFR-TS). Resistance in the most important human parasite, Plasmodium falciparum, initially results from an S108N mutation in the DHFR domain, with additional mutation (most commonly C59R or N51I or both) imparting much greater resistance. From a homology model of the 3-D structure of DHFR-TS, rational drug design techniques have been used to design and subsequently synthesize inhibitors able to overcome malarial pyrimethamine resistance. Compared to pyrimethamine (Ki 1.5 nM) with purified recombinant DHFR fromP. falciparum, the Ki value of the m-methoxy analogue of pyrimethamine was 1.07 nM, but against the DHFR bearing the double mutation (C59R + S108N), the Ki values for pyrimethamine and the m-methoxy analogue were 71.7 and 14.0 nM, respectively. The m-chloro analogue of pyrimethamine was a stronger inhibitor of both wild-type DHFR (with Ki 0.30 nM) and the doubly mutant (C59R +S108N) purified enzyme (with Ki 2.40 nM). Growth of parasite cultures of P. falciparum in vitro was also strongly inhibited by these compounds with 50% inhibition of growth occurring at 3.7 microM for the m-methoxy and 0.6 microM for the m-chloro compounds with the K1 parasite line bearing the double mutation (S108N + C59R), compared to 10.2 microM for pyrimethamine. These inhibitors were also found in preliminary studies to retain antimalarial activity in vivo in P. berghei-infected mice.

A general strategy is outlined for the obtention of the various skeletons of the Amaryllidaceae alkaloids based upon the Diels-Alder addition of a benzoquinone to an alkoxycyclohexa-1,3-diene and subsequent acid catalysed rearrangement of the adduct. The approach is exemplified by the synthesis of the lycoramine system.

Photolysis of fluphenazine, a competitive inhibitor of trypanothione reductase in the presence of trypanothione reductase leads to irreversible, time-dependent inactivation, which is not dependent on the presence of molecular oxygen in the medium and can be pretected against by the presence of trypanothione substrate; MALDI and electrospray mass spectrometric analyses shows that 2–5 equiv. of the phenothiazine are incorporated per enzyme subunit.

The preparation of 2-hydroxytetrahydropyran-2,6-dicarboxylic acid (6S-1), 2-hydroxytetrahydrofuran-2,5-dicarboxylic acid (17), and 3,3-difluoro-2-hydroxytetrahydropyran-2,6-dicarboxylic acid (26), three transition state analogs of hydrated tetrahydrodipicolinic acid (THDPA) and a depsipeptide derivative (11) of 6S-1 is described

A general strategy is outlined for the obtention of the various skeletons of the Amaryllidaceae alkaloids based upon the Diels-Alder addition of a benzoquinone to an alkoxycyclohexa-1,3-diene and subsequent acid catalysed rearrangement of the adduct. The approach is exemplified by the synthesis of the lycoramine system.

The treatment of l, 2, 3, 4, 4a, 9b-hexahydro-3, 8-dihydroxy-7-methoxy-9b-(2'-methoxyethyl)dibenzofuran with chloroform and aqueous potassium hydroxide under conventional Reimer-Tiemann reaction conditions resulted in the replacement of the 7-methoxyl group by a carbaldehyde one. A choice between alternative pathways for this novel displacement has been facilitated by examination of the behaviour of the corresponding 7-trideuteromethoxy compound. Dichlorocarbene attack at position 7 rather than at the unsubstituted position 9 is shown to be due to steric encumbrance at the latter site.

The readily available alkenes (4) and (5) were coupled using a palladium(II) catalyst to give the diene ester (6), a late-stage intermediate to 13-HODE.