Human thymidylate synthetase--III. Effects of methotrexate and folate analogs

The structure-activity relationship of human thymidylate synthetase (EC 2.1.1.45) was studied with two groups of folate analogs: (1) methotrexate (MTX) analogs modified at the glutamate residue and N¹⁰; and (2) tetrahydrofolate (H₄PteGlu) analogs modified at N⁵ and N¹⁰. With respect to MTX analogs, it was found that: (1) substitution of the glutamate side chain by α-aminoadipic acid. α-aminopimelic acid or β-aminoglutaric acid slightly affects its K_i; (2) a free α-carboxyl group on the amino acid side chain of MTX, or any free carboxyl group in that vicinity plays an important role in the inhibitory potency of MTX analogs to the enzyme; (3)esterification or amidation of the α-carboxyl group of MTX decreases the inhibitory potency; and (4) free aspartyl or glutamyl conjugation through a peptide linkage to the γ-carboxyl group of the glutamate side chain decreases its K_i to the enzyme by 5- and 8-fold respectively. Tetrahydrofolate analogs formed by inserting an ethylene, iminyl or a carbonyl bridge between the nitrogen at N⁵ and N¹⁰ or by substitution at the N⁵ position were found to be poor inhibitors under our assay conditions.     

Alanine-scanning mutagenesis of transmembrane domain 6 of the M(1) muscarinic acetylcholine receptor suggests that Tyr381 plays key roles in receptor function.

Transmembrane domain 6 of the muscarinic acetylcholine (ACh) receptors is important in ligand binding and in the conformational transitions of the receptor but the roles of individual residues are poorly understood. We have carried out a systematic alanine-scanning mutagenesis study on residues Tyr381 to Val387 within the binding domain of the M(1) muscarinic ACh receptor. The seven mutations were then analyzed to define the effects on receptor expression, agonist and antagonist binding, and signaling efficacy. Tyr381Ala produced a 40-fold reduction in ACh affinity and a 50-fold reduction in ACh-signaling efficacy. Leu386Ala had similar but smaller effects. Asn382Ala caused the largest inhibition of antagonist binding. The roles of the hydroxyl group and benzene ring of Tyr381 were probed further by comparative analysis of the Tyr381Phe and Tyr381Ala mutants using three series of ligands: ACh analogs, azanorbornane- and quinuclidine-based ligands, and atropine analogs. These data suggested that the hydroxyl group of Tyr381 is primarily involved in forming hydrogen bond interactions with the oxygen atoms present in the side chain of ACh. We propose that this interaction is established in the ground state and preserved in the activated state of the receptor. In contrast, the Tyr381 benzene ring may form a cation-pi interaction with the positively charged head group of ACh that contributes to the activated state of the receptor but not the ground state. However, the hydroxyl group and benzene ring of Tyr381 both participate in interactions with azanorbornane- and quinuclidine-based ligands and atropine analogs in the ground state as well as the activated state of the receptor.     

Substituent effects of N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamides on positive allosteric modulation of the metabotropic glutamate-5 receptor in rat cortical astrocytes

CDPPB [3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide] was recently described as the first centrally active, positive allosteric modulator of rat and human metabotropic glutamate receptor (mGluR) mGluR5 subtype. We explored the structural requirements for potentiation of glutamate-induced calcium release in naturally expressed mGluR5 in cultured rat astrocytes and increasing affinity for the allosteric antagonist binding site by evaluating 50 analogues of CDPPB. In the fluorometric calcium assay, CDPPB exhibited an EC50 value of 77 +/- 15 nM in potentiating mGluR5-mediated responses in cortical astrocytes and a Ki value of 3760 +/- 430 nM in displacing [3H]methoxyPEPy binding in membranes of cultured HEK-293 cells expressing rat mGluR5. The structure-activity relationships showed that electronegative aromatic substituents in the para-position of the benzamide moiety of CDPPB increase potency. Both binding and functional activities were further increased with a halogen atom in the ortho-position of the 1-phenyl ring. These effects of substitution do not match those of either aromatic ring of MPEP [2-methyl-6-(phenylethynyl)pyridine] for the antagonist allosteric binding site. Combination of the optimal substituents and aromatic positions resulted in 4-nitro-N-(1-(2-fluorophenyl)-3-phenyl-1H-pyrazol-5-yl)benzamide (VU-1545) showing Ki = 156 +/- 29 nM and EC50 = 9.6 +/- 1.9 nM in the binding and functional assays, respectively.     

Design,Synthesis and Evaluation of Rhodanine Derivatives as Aldose Reductase Inhibitors

Aldose reductase (ALR) enzyme plays a significant role in conversion of excess amount of glucose into sorbitol in diabetic condition, inhibitors of which decrease the secondary complication of diabetes mellitus. To understand the structural interaction of inhibitors with ALR enzyme and develop more effective ALR inhibitors, a series of substituted 5-phenylbenzoate containing N-substituted rhodanine derivatives were synthesized and evaluated for their in vitro ALR inhibitory activity. Docking studies of these compounds were carried out, which revealed that the 5-phenylbenzoate moiety deeply influenced the key π-π stacking while 4-oxo-2-thioxothiazolidines contributed in hydrogen bond interactions. The phenyl ring of benzylidene system occupied in specific pocket constituted from Phe115, Phe122, Leu300 and Cys303 while the rhodanine ring forms a tight net of hydrogen bond with Val47 at anionic binding site of the enzyme. The structural insights obtained from the docking study gave better understanding of rhodanine and macromolecular interaction and will help us in further designing and improving of ALR inhibitory activity of rhodanine analogs.     

Polychlorinated biphenyls as phenobarbitone-type inducers of microsomal enzymes: Structure-activity relationships for a series of 2,4-dichloro-substituted congeners

Several polychlorinated biphenyl (PCB) isomers and congeners resemble phenobarbitone (PB) in their mode of induction of the hepatic drug-metabolizing enzymes; however, unlike PCBs which induce aryl hydrocarbon hydroxylase, no apparent structure-activity correlations have been reported. This study examines the effects of structure on the activity of a series of 2,4-dichloro-substituted biphenyls as inducers of several microsomal enzyme activities including dimethylaminoantipyrine N-demethylase, benzo[a]pyrene hydroxylase, aldrin epoxidase, and ethoxyresorufln O-deethylase. The results clearly illustrate a marked effect of structure on activity: all of the 2,4-dichloro-substituted PCBs resembled PB in their mode of induction. However, the potency of the induction response was dependent on the substitution pattern of the second phenyl ring (i.e. 2,3,4,5-tetrachloro ? 2,3,4,5,6-pentachloro > 2,3,4,6-tetrachloro > 2,3,5,6-tetrachloro > 2,4,6-trichloro); the structure of the lower chlorinated ring also determined induction potency since the 2,4-dichloro-substituted PCBs were generally more active than their 4-chloro-substituted analogs, whereas the 2-substituted PCB homologs were inactive. The structural factors which typify the most active PB-type inducer, 2,2′,3,4,4′,5-hexachlorobiphenyl, include the presence of two para-, at least two meta- and two ortho-chloro substituents. In addition to the structure-activity correlations noted for PCBs, the 2,2′,3,4,4′,5-hexa-chlorobiphenyl congener also elicited a dose-response induction of two PB-inducible enzymes, aldrin epoxidase and dimethylaminoantipyrine N-demethylase.     

Synthesis of pyrimido[1,4]diazepin‐2‐one analogs and their evaluation as anticonvulsant agents

5‐Benzyloxycarbonylaminomethylcarbonyl(N‐methyl)amino‐4‐[2‐chloro(2‐fluoro or 2‐hydrogen)benzoyl]pyrimidines (compound 14 ) in which the chlorophenyl moiety of dipeptidoaminochlorobenzophenones ( 1 ) is replaced by a pyrimido ring, and 1,3‐dihydro‐1‐methyl‐5‐[2‐chloro (2‐fluoro or 2‐hydrogen)phenyl]‐2H‐pyrimido[5,4‐e][1,4]diazepin‐2‐ones ( 16 ) in which the chlorophenyl moiety of 7‐chloro‐5‐aryl‐benzo[1,4]diazepin‐2‐one ( 3 ) is replaced by a pyrimido ring, were synthesized and evaluated as anticonvulsants by using the subcutaneous metrazol‐ (Met) and maximal electroshock– (MES) induced seizure screening tests. Structure‐activity studies showed these two classes of compounds ( 14, 16 ) are generally more potent in the Met screen relative to the MES screen. The effect which the nature of the benzoyl C‐4 ortho‐substituent (Cl, F, H) in compound 14 , or the ortho‐phenyl C‐5 substituent (Cl, F. H) in compounds 16 , has upon anticonvulsant activity was small with the potency profile generally being Cl ≅ F > H. It is proposed that 5‐benzyloxycarbonylaminocarbonyl(N‐methyl)amino‐4‐(2‐fluorobenzoyl)pyrimidine ( 14b ) may act as a prodrug, at least in part, to 1,3‐dihydro‐1‐methyl‐5‐(2‐fluorophenyl)‐2H‐pyrimido[5,4‐e][1,4]diazepin‐2‐one ( 16b ), because 14b does not bind to the benzodiazepine receptor binding site(s), yet it is approximately equipotent to 16b in the Met and MES screens. Compounds 14b and 16b are less active than clonazepam but more active than valproic acid in the Met screen, and less active than phenytoin but more active than clonazepam and valproic acid in the MES screen. Drug Dev. Res. 46:155–162, 1999. © 1999 Wiley‐Liss, Inc.     

Binding of 2′,5′-dideoxyadenosine to brain membranes: Comparison to P-site inhibition of adenylate cyclase

Membranes from rat cerebral cortex and striatum contain a relatively large number of high-affinity binding sites for [³H]2′,5′-didepxyadenosine, [³H]adenine arabinoside, and [³H]adenosine. The binding of [³H]2′,5′-dideoxyadenosine and [³H]adenine arabinoside was virtually unaffected by relatively specific agonists and antagonists for adenosine receptors, such as 2-chloroadenosine, N⁶-phenylisopropyladenosine or theophylline. Binding of [³H]adenosine was partially blocked by such receptor ligands. The specific binding of all three ligands was antagonized by a variety of adenosine analogs which inhibit adenylate cyclase by interaction with the so-called P-site associated with this enzyme. However, potencies of adenosine analogs as P-site inhibitors of adenylate cyclase and as antagonists of binding do not correlate well. 5′-Methylthioadenosine had high potency and efficacy versus binding of [³H]2′,5′-dideoxyadenosine but had virtually no effect on activity of adenylate cyclase. 2-Fluoroadenosine was less potent than adenosine as an antagonist of specific binding of [³H]2′,5′-dideoxyadenosine, which 2-fluoroderivatives of adenosine, adenine arabinoside and adenine xylofuranoside were more potent than the parent compounds as P-site inhibitors. The significance of the binding sites for [³H]2′,5′-dideoxyadenosine remains unclear, but their presence complicates the use of [³H]adenosine and certain analogs as ligands for adenosine membrane sites associated with adenylate cyclase.     

Structure-activity relationship of neurokinin A(4-10) at the human tachykinin NK(2) receptor: the effect of amino acid substitutions on receptor affinity and function

A structure-activity study of the neurokinin A (NKA) fragment NKA(4-10) was performed to investigate the importance of amino acid residues for receptor efficacy, potency and affinity at the NK(2) receptor in human colon circular muscle. Fourteen analogs of NKA(4-10) were produced with substitutions at positions 4, 5, 7, 9 and/or 10 of NKA. Their potencies were determined by in vitro contractile responses and affinities by radioligand binding using [125I]NKA. Functional potency was enhanced 8-fold by single amino acid substitutions with Lys(5) and MeLeu(9) but not significantly altered by substitutions Glu(4), Arg(5), His(5) and Nle(10). The multiply-substituted analogs [MeLeu(9),Nle(10)]NKA(4-10), [Lys(5),MeLeu(9),Nle(10)]NKA(4-10) and [Lys(5),(Tyr(7)),MeLeu(9),Nle(10)]NKA(4-10) displayed 6-9-fold increase in potency. Although [Arg(5),Nle(10)]NKA(4-10) was similar in potency to NKA(4-10), it was the only analog to show significantly reduced efficacy. All analogs were able to compete fully for [125I]NKA binding. [Lys(5),MeLeu(9)]NKA(4-10), [MeLeu(9),Nle(10)]NKA(4-10), [Lys(5),Nle(10)]NKA(4-10) and analogs containing single substitutions with Glu(4), Arg(5), Lys(5) and MeLeu(9) displayed significantly higher affinity, whereas those with Nle(10) and [Glu(4),Nle(10)] substitutions showed significantly lower affinity than NKA(4-10). There was a positive correlation (r=0.63) between binding affinity and functional potency, which was markedly improved (r=0.95) by removal of three analogs: [Lys(5),MeLeu(9),Nle(10)]NKA(4-10), [Lys(5),Tyr(7),MeLeu(9),Nle(10)]NKA(4-10) and [Lys(5),Tyr(I(2))(7),MeLeu(9),Nle(10)]NKA(4-10). These exhibited similar binding affinities to that of NKA(4-10) but were more potent in functional studies, possibly indicating a different mechanism of receptor interaction. In conclusion, substitution of Ser(5) with Lys, and/or N-methylation of Leu(9), were the most effective changes to increase functional and binding potency of NKA(4-10) at the human colon NK(2) receptor.     

β-Endorphin

Three β_h-EP analogs which show different extents of alteration in analgesic potency by substitution of a single amino acid residue were assayed for their peripheral opioid activity and the binding to opioid μ-receptor to determine the relationships among the opioid activities obtained from different assays. In the guinea pig ileum assay, [Gln⁸]-β_h-EP showed a higher inhibitory activity than the parent peptide. [Tyr³¹]-analog had the same potency as β_h-EP, while [Trp²⁷]-analog retained only one fourth the potency of β_h-EP. Assayed on the vas deferens of the mouse and the rat, all three substituted β_h-EP analogs exhibited a lower potency than their parent peptide. Receptor binding assay using [³H]-dihydromorphine as the primary ligand showed that [Gln⁸]-analog had a binding potency 1.5-fold that of β_h-EP, while the potencies of [Tyr³¹]- and [Trp²⁷]-analogs were not significantly different from that of the parent peptide. No correlation in relative potency was found between vas deferens assays and their μ-receptor binding or analgesic activity. However, the relative potencies of binding to μ-receptor in [Gln⁸]- and [Tyr³¹]-analogs were found to be consistent with those of analgesic and guinea pig ileum assays, whereas the binding to β-EP receptor of all analogs appeared to be related to the charge properties of β-EP molecule.     

Synthesis and anticonvulsant activity of some N-(benzoyl)glycinanilide derivatives

Glycine is a major inhibitory neurotransmitter and recent studies have shown that certain lipophilic glycine derivatives demonstrate anticonvulsant activity in animal epilepsy models. On the other hand, anilide is another fruitful structure for designing potential anticonvulsant agents. Ameltolide, ralitoline and some phthalimide derivatives are the examples of anilide analogs with potent anticonvulsant activity. In this study, two key structural pharmacophores were combined and a series of N-benzoylglycinanilide derivatives were designed. Their anticonvulsant activities evaluated against maximal electroshock (MES) and subcutaneous metrazole seizure tests, whereas their neurotoxicity was examined by rotarod test. The preliminary screening results indicated that majority of the compounds were effective in the MES test. None of the compounds showed neurotoxicity according to the rotarod test at studied doses. The most active compound in the series is N-(2-((4-methoxyphenyl)amino)-2-oxoethyl)benzamide (compound 8) which bearing 4-methoxy substituent on the N-phenyl ring.     

Vasoactivities of adenosine analogues in trout gill (salmo gairdneri R.)

Various adenosine analogues phosphorylated or not, modified at the purine ring level or in the carbohydrate moiety, have been tested for their ability to induce a vasoconstriction in the arterio-arterial vascular bed of the trout gill. The structural integrity of the purine ring and the N-glycosidic bond are required for activity. The anti conformation of the molecule is preferable to the syn conformation. The basicity and/or the hydrogen bonding capabilities at the 6-position are important for the potency of the molecule. Substitutions which decrease the basicity of the 1-position decrease the activity and substitutions which reinforce the basicity (2-Cl adenosine) increase it. Alterations of the furanose ring conformation and the reduction of the hydrogen bonding capabilities of the 2′- and 3′-hydroxyls decrease the potency of the compound. Some substitutions in the 5′-position intensify the haemodynamic response. Thus, 5′-ethyl carboxamide adenosine is one order of magnitude more potent than adenosine. The addition of more than one phosphate in 5′-position (ADP, ATP) favours the effectiveness of the compound but a further elongation of the phosphate chain does not improve its potency. The α-β configuration of the phosphate chain is essential for the physiological effect. IMP, adenylosuccinate and all cyclic necleotides are devoid of haemodynamic activity. These results sustain the hypothesis of the presence of specific vascular purinergic receptors in the trout gill.     

Novel 2-substituted cocaine analogs: binding properties at dopamine transport sites in rat striatum

A novel scheme utilizing vinylcarbenoid precursors has been developed for the synthesis of novel tropane analogs of cocaine. Using this method, 15 analogs were prepared and tested for activity in binding to dopamine transporters in rat striatal membranes using [¹²⁵I]RTI-55. In all the analogs, the aryl group at the 3 position was directly bound to the tropane ring (as in WIN 35,428), and methyl or ethyl ketone moieties were present at the 2 position instead of the typical ester group. The most potent analog was a 2-naphthyl derivative (IC₅₀ value of 0.2 nM, vs. 170 nM for cocaine), while replacement of the aryl with either ethyl or cyclohexyl drastically reduced potency (to > 50 μM and 5 μM, respectively).     

Interactions of kinins with angiotensin I converting enzyme (kininase II)

Angiotensin I converting enzyme (ACE) was purified to homogeneity from porcine kidney in order to determine whether iodobradykinins bind to the enzyme and, if so, whether pGlu-Trp-Pro-Arg-Pro-Gin-Ile-Pro-Pro, SQ20881, a competitive ACE inhibitor, changes the conformation of the enzyme in such a way that it binds kinins with an affinity and specificity expected of a bradykinin (BK) receptor, i.e. where the BK potentiating action of SQ20881 involves an increase in the number of BK receptors due to a conformational change in ACE. 125I-Labeled derivatives of [Tyr1]-kallidin and [Tyr-8]-bradykinin bound to the EDTA-inhibited enzyme, and binding was inhibited by nonradioactive BK. [125I-Tyr5]-BK was not bound by the enzyme. Specificity of [125I-Tyr5]-kallidin (T1K) binding was tested with forty-eight BK analogs, and the concentrations of analogs that inhibited 50% of T1K binding were determined. BK at 1.6 +/- 0.3 X 10(-8) M inhibited 505 of T1K binding. In addition, the concentrations of analogs that decreased by 50% the rate of [3H]-Hip-Gly-Gly ([3H]-HGG) hydrolysis by ACE were assessed. BK at 1.2 +/- 0.2 X 10(-6) M decreased the rate of [3H]-HGG hydrolysis by 50%. A comparison between these concentrations of analogs for inhibition of T1K binding and [3H]-HGG hydrolysis yielded a high correlation coefficient (r = 0.85). The specificity of ACE binding was clearly different from that expected of a BK receptor. Compounds structurally unrelated to BK, such as 5Q20881, pGlu-Lys-Trp-Ala-Pro-OH (BPP5a) and angiotensin I, inhibited T1K binding and [3H]-HGG hydrolysis by ACE.     

The selective activation of the glutamate receptor GluR5 by ATPA is controlled by serine 741

Only a few agonists exhibit selectivity between the AMPA and the kainate subtypes of the glutamate receptor. The most commonly used kainate receptor preferring agonist, (S)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid [(S)-ATPA], is an (R,S)-2-amino-3-(5-methyl-3-hydroxy-4-isoxazolyl)propionic acid (AMPA) derivative in which the methyl group at the 5-position of the isoxazole ring has been replaced by a tert-butyl group. When characterized by the two-electrode voltage clamp method in Xenopus laevis oocytes, ATPA exhibits at least 50-fold higher potency on the kainate receptor subtype, GluR5, compared with the AMPA receptors. Through mutagenesis studies of GluR5 and the AMPA receptor subtype, GluR1, we demonstrate that this pronounced selectivity for ATPA can be ascribed to Ser741 in GluR5 and Met722 in GluR1. Examination of other aliphatic substitutions at the 5-position of the isoxazole ring revealed that (R,S)-2-amino-3-(5-isopropyl-3-hydroxy-4-isoxazolyl)propionic acid (isopropyl-AMPA) displayed a 6-fold higher potency for GluR5 than for GluR1, whereas the analogs, propyl-AMPA and isobutyl-AMPA, did not exhibit significantly different potencies. Our study suggests that the GluR5 selectivity was a result not only of steric interference between the bulky tert-butyl group in ATPA and the methionine (Met722) in GluR1 but also a serine-dependent stabilization of the active conformation of GluR5 induced by ATPA. The stabilization was agonist-dependent and observed only for ATPA and isopropyl-AMPA, not for other AMPA analogs with bulky substitutions at the 5-position of the isoxazole ring.     

Comparative study of analgesia induced by N VAL5- and Pro5-enkephalin analogs

We have compared the analgesic potency of N-Val5 analogs and Pro5 derivatives in order to identify the mechanism of the unusually strong antinociceptive activity induced by Pro5 enkephalin analogs. Whereas N-Val5 and Pro5 compounds are equiactive in in vitro assays, N-Val5 derivatives are considerably less active analgesics than Pro5 analogs. Since N-Val is the homolog of Pro with an opened pyrrolidine ring, these data show that the cyclic structure of Pro participates in the strong in vivo activity of Pro5 analogs without altering the binding to the opiate receptor.     

N‐pyridin‐2‐yl benzamide analogues as allosteric activators of glucokinase: Design,synthesis, in vitro,in silico and in vivo evaluation

Glucokinase (GK) is the key enzyme controlling levels of blood glucose under normal physiological range, and GK activators are emerging class of drug candidates with promising hypoglycaemic activity. The current study was planned to design, synthesize and evaluate novel N‐pyridin‐2‐yl benzamide analogues as allosteric activators of GK. A novel series of N‐pyridin‐2‐yl benzamide analogues were synthesized starting from 3‐nitrobenzoic acid and evaluated in vitro for GK activation followed by in silico studies to predict the binding interactions of the designed molecules with GK protein. The selected synthesized molecules (compounds 5b , 5c , 5e , 5g , 5h and 6d ) which displayed excellent GK activity (GK fold activation around 2) in GK assay and appreciable binding interaction with GK in docking studies were further evaluated for their antihyperglycaemic potential using oral glucose tolerance test (OGTT) in rats. Amongst the compounds tested in vivo (OGTT assay) for antihyperglycaemic potential, compounds 5c , 5e and 5g displayed significant reduction in blood glucose levels. Compound 5e displayed most significant antidiabetic activity and comparable to that of standard drug in animal studies. The N‐pyridin‐2‐yl benzamide analogues discovered in the current study can provide some lead molecules for the development of potent oral GK activators with minimum side‐effects for the management of type 2 diabetes.     

β-Endorphin: Synthesis and properties of analogs with replacement of lysine residues by arginine

Human β-endorphin analogs, [Arg^{9,19,24,28,29}]-β-endorphin (I) and [Arg^24,28,29]-β-endorphin (II), have been synthesized by the solid-phase method. Peptide II had 86% of the analgesic potency and 216% of the receptor binding activity of the parent molecule. Peptide I had only 18% analgesic potency but its binding activity was more than three time greater than that of human β-endorphin.     

Effect of modification of the 1-, 2-, and 6-positions of 9-beta-D-ribofuranosylpurine cyclic 3',5'-phosphate on the cyclic nucleotide specificity of adenosine cyclic 3',5'-phosphate- and guanosine cyclic 3',5'-phosphate-dependent protein kinases

A group of analogs of adenosine cyclic 3′,5′-phosphate (cAMP) and guanosine cyclic 3′,5′-phosphate (cGMP) with modifications in the 1-, 2- (or N²), and 6 (or N⁶)-positions of the purine ring were compared as activators of a cAMP-dependent protein kinase [PK(cAMP)] from bovine brain and of cGMP-dependent protein kinase [PK(cGMP)] from lobster tail muscle. The results suggest that the 6-amino group of cAMP is not required for the activation of PK(cAMP) by cAMP and that the 6-oxygen and 2-amino moieties of cGMP are required for the activation of PK(cAMP) by cAMP aIn the case of PK(cGMP) activation by cGMP, the 6-oxygen apparently accepts a proton from the enzyme and the 2-amino group apparently donates a proton to the enzyme.     

Synthesis and preliminary in vitro activity of mono- and bis-1H-1,2,3-triazole-tethered β-lactam–isatin conjugates against the human protozoal pathogen Trichomonas vaginalis

In this study, we describe the synthesis of mono- and bis-1H-1,2,3-triazole-tethered β-lactam–isatin conjugates using copper-catalysed azide-alkyne cycloaddition reaction between mono- and di-propargylated azetidin-2-ones and N-alkylazido isatins. The synthesized conjugates were evaluated for their preliminary in vitro analysis against Trichomonas vaginalis at 50 μM. The efficacy of synthesized hybrids was observed to depend on the substituent at N-1 position of β-lactam ring, as well as the presence of single/double 1H-1,2,3-triazole linker. Among the synthesized conjugates, the presence of a p-tolyl substituent at N-1 of β-lactam ring was preferred for good activity profiles while the increase in spacer length did not influence the efficacy of the compounds. Compounds with high levels of potency were further analysed to determine their IC₅₀ values, as well as cytotoxicity profiles against mammalian cells. The most active compound in the synthesized conjugates displayed an IC₅₀ value of 10.49 μM against cultured G3 strain of T. vaginalis and was non-toxic to cultured mammalian HeLa cells at the same concentration.