Analogues of thiolactomycin as potential anti-malarial and anti-trypanosomal agents

A series of analogues of the naturally occurring antibiotic thiolactomycin (TLM) have been synthesised and evaluated for their ability to inhibit the growth of the malaria parasite, Plasmodium falciparum. Thiolactomycin is an inhibitor of Type II fatty acid synthase which is found in plants and most prokaryotes, but not an inhibitor of Type I fatty acid synthase in mammals. A number of the analogues showed inhibition equal to or greater than TLM. The introduction of hydrophobic alkyl groups at the C3 and C5 positions of the thiolactone ring lead to increased inhibition, the best showing a fourteenfold increase in activity over TLM. In addition, some of the analogues showed activity when assayed against the parasitic protozoa, Trypanosoma cruzi and Trypanosoma brucei.     

Synthesis and biological evaluation of a C5-biphenyl thiolactomycin library

Fifteen novel C5 analogues of thiolactomycin (13 biphenyl analogues and two biphenyl mimics) have been synthesised and assessed for their in vitro mtFabH and whole cell Mycobacterium bovis BCG activity, respectively. Analysis of the 15 compounds revealed that six possessed enhanced in vitro activity in a direct mtFabH assay. Encouragingly analogues 11, 12 and 13 gave a significant enhancement in in vitro activity against mtFabH. Analogue 13 (5-(4-methoxycarbonyl-biphenyl-4-ylmethyl)-4-hydroxy-3,5-dimethyl-5H-thiophen-2-one) gave an IC(50) value of 3 microM compared to the parent drug thiolactomycin (75 microM) against mtFabH. The biological analysis of this library reaffirms the requirement for a linear pi-rich system containing hydrogen bond accepting substituents attached to the para-position of the C5 biphenyl analogue to generate compounds with enhanced activity.     

Antitubercular agents. Part 2: new thiolactomycin analogues active against Mycobacterium tuberculosis

Structurally modified analogues of naturally occurring antibiotic thiolactomycin, substituted at 4-position of the thiolactone ring have been prepared and evaluated for their antitubercular activity. Some of the compounds have exhibited potential activity against Mycobacterium tuberculosis.     

Acetylene-based analogues of thiolactomycin, active against Mycobacterium tuberculosis mtFabH fatty acid condensing enzyme

Analogues of the natural antibiotic thiolactomycin, with acetylene-based side chains, have the highest recorded in vitro inhibitory activity against the recombinant Mycobacterium tuberculosis beta-ketoacyl-ACP synthase mtFabH condensing enzyme. In particular, 5-[3-(4-acetyl-phenyl)-prop-2-ynyl]-4-hydroxy-3,5-dimethyl-5H-thiophen-2-one exhibited more than an 18-fold increased potency, compared to thiolactomycin, against this key condensing enzyme, involved in M. tuberculosis mycolic acid biosynthesis. Analogues of the antibiotic thiolactomycin, with acetylene-based side chains, have the highest recorded activity against cloned mtFabH condensing enzyme.     

Biphenyl-based analogues of thiolactomycin, active against Mycobacterium tuberculosis mtFabH fatty acid condensing enzyme

Analogues of the antibiotic thiolactomycin, with biphenyl-based 5-substituents, were found to have excellent in vitro inhibitory activity against the recombinant Mycobacterium tuberculosis beta-ketoacyl-ACP synthase mtFabH condensing enzyme. In particular, 5-(4'-benzyloxy-biphen-4-ylmethyl)-4-hydroxy-3,5-dimethyl-5H-thiophen-2-one exhibited approximately a 4-fold increased potency against this key condensing enzyme involved in M. tuberculosis mycolic acid biosynthesis, compared to thiolactomycin.     

Thiolactomycin analogues as potential anti-Toxoplasma gondii agents

The discovery of new compounds active against Toxoplasma gondii is extremely important due to the severe disease caused by this pathogen in immunocompromised hosts and to congenital infection. Type II fatty acid biosynthesis has shown to be a promising target for drug intervention in toxoplasmosis. Here we describe the inhibitory effect of 8 thiolactomycin (TLM) analogues against tachyzoite-infected LLC-MK₂ cells. The TLM analogues demonstrated anti-T. gondii activity, arresting tachyzoite proliferation with IC₅₀ values in the micromolar level after 24 h and 48 h of treatment. Metabolic labelling of extracellular parasites treated with TLM analogues using [³H]acetate demonstrated that these drugs affected acylglycerol synthesis. The rapid reduction of parasite load suggests that these compounds have selective cytotoxic effects against T. gondii. Transmission electron microscopy demonstrated that TLM analogues interfered with membrane-bounded organelles and parasite division and this in turn affected parasite development and survival.     

Muraymycins,novel peptidoglycan biosynthesis inhibitors: synthesis and SAR of their analogues

A series of Muraymycin analogues was synthesized. These analogues showed excellent antimicrobial activity against gram-positive organisms. These analogues also showed excellent inhibitory activity against the target peptidoglycan biosynthesis enzyme MraY, the cell membrane associated transglycosylase responsible for the formation of Lipid II.     

β-Ketoacyl-acyl carrier protein synthase III from pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.): properties,inhibition by a novel thiolactomycin analogue and isolation of a cDNA clone encoding the enzyme

A beta-ketoacyl-acyl carrier protein (ACP) synthase III (KAS III; short-chain condensing enzyme) has been partly purified from pea leaves. The enzyme, which had acetyl-CoA:ACP acyltransferase (ACAT) activity, was resolved from a second, specific, ACAT protein. The KAS III enzyme had a derived molecular mass of 42 kDa (from its cDNA sequence) and operated as a dimer. Its enzymological characteristics were similar to those of two other plant KAS III enzymes except for its inhibition by thiolactomycin. A derivative of thiolactomycin containing a longer (C8 saturated) hydrophobic side-chain (compound 332) was a more effective inhibitor of pea KAS III and showed competitive inhibition towards malonyl-ACP whereas thiolactomycin showed uncompetitive characteristics at high concentrations. This difference may be due to the better fit of compound 332 into a hydrophobic pocket at the active site. A full-length cDNA for the pea KAS III was isolated. This was expressed in Escherichia coli as a fusion protein with glutathione S-transferase in order to facilitate subsequent purification. Demonstrated activity in preparations from E. coli confirmed that the cDNA encoded a KAS III enzyme. Furthermore, the expressed KAS III had ACAT activity, showing that the latter was inherent. The derived amino acid sequence of the pea cDNA showed 81-87% similarity to that for other plant dicotyledon KAS IIIs, somewhat less for Allium porrum (leek, 71%) and for Porphyra spp. (62%), Synechocystis spp. (65%) and various bacteria (42-65%). The pea KAS III exhibited four areas of homology, three of which were around the active-site Cys(123), His(323) and Asn(353). In addition, a stretch of 23 amino acids (residues 207-229 in the pea KAS III) was almost completely conserved in the plant KAS IIIs. Modelling this stretch showed they belonged to a peptide fragment that fitted over the active site and contained segments suggested to be involved in substrate binding and in conformational changes during catalysis, as well as an arginine suggested to participate in the acid-base catalytic mechanism.     

Acetoacetyl-acyl carrier protein synthase. A target for the antibiotic thiolactomycin

The biochemical basis for the inhibition of fatty acid biosynthesis in Escherichia coli by the antibiotic thiolactomycin was investigated. A biochemical assay was developed to measure acetoacetyl-acyl carrier protein (ACP) synthase activity, a recently discovered third condensing enzyme from E. coli (Jackowski, S., and Rock, C.O. (1987) J. Biol. Chem. 262, 7927-7931). In contrast to the other two condensing enzymes in E. coli, acetoacetyl-ACP synthase (synthase III) condensed malonyl-ACP with acetyl-CoA, rather than with acetyl-ACP. The concentration dependence of thiolactomycin inhibition of fatty acid biosynthesis in vivo was the same as the inhibition of acetoacetyl-ACP synthase activity in vitro indicating that the two phenomena were related. A thiolactomycin-resistant mutant (strain CDM5) was isolated. The specific activity of acetoacetyl-ACP synthase in extracts from this mutant was 10-fold lower than in extracts from its thiolactomycin-sensitive parent resulting in a marked defect in the ability of strain CDM5 to incorporate acetyl-CoA into fatty acids in vitro. The residual acetoacetyl-ACP synthase activity in the resistant strain was refractory to thiolactomycin inhibition. In addition, acetyl-CoA:ACP transacylase activity in strain CDM5 was resistant to inactivation by thiolactomycin suggesting that the acetoacetyl-ACP synthase also catalyzes this transacylation reaction. These data point to acetoacetyl-ACP synthase as a target for thiolactomycin inhibition of bacterial fatty acid biosynthesis.     

Synthesis and antimicrobial activity of novel globomycin analogues

Globomycin, a signal peptidase II inhibitor, and its derivatives show potent antibacterial activity against Gram-negative bacteria. The synthesis and antimicrobial activity of novel globomycin analogues are reported. One of the analogues showed a more potent activity against Gram-negative bacteria than globomycin and also exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).     

Synthesis and biological activity of enantiomeric pairs of 5-vinylthiolactomycin congeners

Twelve enantiomeric pairs of 5-vinylthiolactomycin congeners were synthesized by employing our efficient synthetic route previously explored for the synthesis of enantiomeric pairs of thiolactomycin and its 3-demethyl derivative. From the biological activity assay carried out using the obtained congeners along with enantiomeric pairs of thiolactomycin and its 3-demethyl derivative previously prepared, it appeared evident that in vitro antibacterial and mammalian type I FAS inhibitory activity of thiolactomycin congeners can be cleanly separated by changing not only the structure but also the absolute configuration of the side chain at the C(5)-position. These studies led us to explore (S)-3-demethyl-5-(pent-1-enyl)thiolactomycin derivative [(S)-4-hydroxy-5-methyl-5-(pent-1-enyl)-5H-thiophen-2-one] which exhibits type I FAS inhibitory activity equal to that of C75, the potent inhibitor so far reported, with complete loss of in vitro antibacterial activity.     

Synthesis and biological evaluation of trifluralin analogues as antileishmanial agents

A series of new analogues of trifluralin (TFL) were synthesized and characterized in view of changing the unfavorable properties that limits its use as antileishmanial agent. Some of the TFL analogues display more activity than a standard drug (miltefosine) against the promastigote forms of Leishmania infantum and Leishmania donovani and the intracellular form (THP-1 infected with L. infantum). All analogues showed a clear advantage over miltefosine, as they are not hemolytic. Some analogues can conjugate these characteristics with reduced cell toxicity and improved intracellular activity.     

Synthesis and antiparasitic activity of albendazole and mebendazole analogues

Albendazole (Abz) and Mebendazole (Mbz) analogues have been synthesized and in vitro tested against the protozoa Giardia lamblia, Trichomonas vaginalis and the helminths Trichinella spiralis and Caenorhabditis elegans. Results indicate that compounds 4a, 4b (Abz analogues), 12b and 20 (Mbz analogues) are as active as antiprotozoal agents as Metronidazole against G. lamblia. Compound 9 was 58 times more active than Abz against T. vaginalis. Compounds 8 and 4a also shown high activity against this protozoan. Compounds 4b and 5a were as active as Abz. None of the Mbz analogues showed activity against T. vaginalis. The anthelmintic activity presented by these compounds was poor.     

Gallic acid based steroidal phenstatin analogues for selective targeting of breast cancer cells through inhibiting tubulin polymerization

Phenstatin analogues were synthesized on steroidal framework, for selective targeting of breast cancer cells. These analogues were evaluated for anticancer efficacy against breast cancer cell lines. Analogues 12 and 19 exhibited significant anticancer activity against MCF-7, hormone dependent breast cancer cell line. While analogues 10-14 exhibited significant anticancer activity against MDA-MB-231, hormone independent breast cancer cell line. Compound 10 showed significant oestrogen antagonistic activities with low agonistic activity in in vivo rat model. These analogues also retain tubulin polymerization inhibition activity. The most active analogue 10 was found to be non-toxic in Swiss albino mice up to 300 mg/kg dose. Gallic acid based phenstatin analogues may further be optimized as selective anti-breast cancer agents.     

Artepillin C isoprenomics: design and synthesis of artepillin C isoprene analogues as lipid peroxidation inhibitor having low mitochondrial toxicity

We designed and synthesized isoprene analogues of artepillin C, a major component of Brazilian propolis, and investigated the inhibitory activity on lipid peroxidation of rat liver mitochondria (RLM) and RLM toxicity based on isoprenomics. We succeeded in the synthesis of artepillin C isoprene analogues using regioselective prenylation within the range from 22% to 53% total yield. Reactivity of artepillin C and its isoprene analogues with ABTS (2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonate)) radical cations showed only a slight difference among the molecules. The isoprene side-chain elongation analogues of artepillin C showed almost the same inhibitory activity against RLM lipid peroxidation as artepillin C. Artepillin C and its isoprene analogues had very weak RLM uncoupling activity. Moreover, artepillin C and its isoprene analogues exhibited a lower inhibitory activity against adenosine 5'-triphosphate (ATP) synthesis by about two orders of magnitude than the effective inhibitory activity against RLM lipid peroxidation. From these results we conclude that artepillin C isoprene analogues could be potent lipid peroxidation inhibitors having low mitochondrial toxicity. We also conclude that elongation of the isoprene side chain of artepillin C to increase lipophilicity had little influence on the inhibitory activity toward RLM lipid peroxidation.     

Synthesis of new praziquantel analogues: potential candidates for the treatment of schistosomiasis

An efficient synthesis of antischistosomal drug praziquantel and analogues was achieved and the synthetic route designed was to afford structurally diverse analogues for better structure-activity relationship understanding. Total of nineteen PZQ analogues with structural variations at amide, piperazine and aromatic moieties have been synthesized and fully characterized. Among all the new analogues tested for antischistosomal activity, one dimethoxy tetrahydroisoquinoline analogue and two tetrahydro-β-carboline analogues exhibited moderate activity against adult Schistosoma mansoni. Tetrahydro-β-carboline analogues showed moderate activity whereas the presence of p-trifluoromethylbenzoyl and p-toluenesulphonyl moieties resulted in complete suppression of antischistosomal activity.     

Novel C-ring analogues of 20(S)-camptothecin-part-2: synthesis and in vitro cytotoxicity of 5-C-substituted 20(S)-camptothecin analogues.

A series of 5-C-substituted 20(S)-camptothecin analogues were synthesised and evaluated their in vitro anti-cancer activity. Several of these analogues have showed excellent activity against human tumor cell lines.     

Mechanism of action of the antibiotic thiolactomycin inhibition of fatty acid synthesis of Escherichia coli

Thiolactomycin, an antibiotic with the structure of (4S)-(2E,5E)-2,4,6-trimethyl-3-hydroxy-2,5,7-octatriene-4-thiolide, inhibits the incorporation of [14C]acetate into cellular fatty acids of Escherichia coli. This antibiotic inhibits the fatty acid synthetase system of E. coli. However, the fatty acid synthetases from Saccharomyces cerevisiae, Candida albicans and rat liver are insensitive to thiolactomycin. This effect may account for the antibacterial activity of thiolactomycin and for its low toxicity in animals.     

Novel hybrids of 15-membered 8a- and 9a-azahomoerythromycin A ketolides and quinolones as potent antibacterials

A series of novel 6-O-substituted and 6,12-di-O-substituted 8a-aza-8a-homoerythromycin A and 9a-aza-9a-homoerythromycin A ketolides were synthesized and evaluated for in vitro antibacterial activity against a panel of representative erythromycin-susceptible and erythromycin-resistant test strains. Another series of ketolides based on 14-membered erythromycin oxime scaffold was also synthesized and their antibacterial activity compared to those of 15-membered azahomoerythromycin analogues. In general, structure-activity studies have shown that 14-membered ketolides displayed favorable antibacterial activity in comparison to their corresponding 15-membered analogues within 9a-azahomoerythromycin series. However, within 8a-azahomoerythromycin series, some compounds incorporating a ketolide combined with either quinoline or quinolone pharmacophore substructures showed significantly potent activity against a variety of erythromycin-susceptible and macrolide-lincosamide-streptogramin B (MLS(B))-resistant Gram-positive pathogens as well as fastidious Gram-negative pathogens. The best compounds in this series overcome all types of resistance in relevant clinical Gram-positive pathogens and display hitherto unprecedented in vitro activity against the constitutively MLS(B)-resistant strain of Staphylococcus aureus. In addition, they also represent an improvement over telithromycin (2) and cethromycin (3) against fastidious Gram-negative pathogens Haemophilus influenzae and Moraxella catarrhalis.     

Biomimetic synthesis, antimicrobial, antileishmanial and antimalarial activities of euglobals and their analogues

In the present communication, naturally occurring phloroglucinol-monoterpene adducts, euglobals G1-G4 (3b/a and 4a/b) and 16 new analogues (13a/b-18a/b and 19-22) were synthesized by biomimetic approach. These synthetic compounds differ from natural euglobals in the nature of monoterpene and acyl functionality. All of these compounds were evaluated for their antibacterial, antifungal, antileishmanial and antimalarial activities. Analogue 17b possessed good antibacterial activity against methicillin-resistant Staphylococcus aureus, while analogues 19-22 possessed potent antifungal activity against Candida glabrata with IC50s ranging from 1.5 to 2.5 microg/mL. Euglobals along with all synthesized analogues exhibited antileishmanial activity. Amongst these, euglobal G2 (3a), G3 (4a) and analogues 13a and 14a showed potent antileishmanial activity with IC50s ranging from 2.8 to 3.9 microg/mL. Analogue 16a possessed antimalarial activity against chloroquine sensitive D6 clone of Plasmodium falciparum. None of the compounds showed toxicity against mammalian kidney fibroblasts (vero cells) upto the concentration of 4.76 microg/ml.