Simple bi- and tricyclic inhibitors of human steroid 5alpha-reductase

A number of tricyclic thiolactams, bicyclic lactams, and bicyclic thiolactams have been prepared and evaluated in vitro as inhibitors of types 1 and 2 steroid 5alpha-reductase. The tricycles with an 8-chloro substituent in the C-ring are nM (IC50) inhibitors of type 1 steroid 5alpha-reductase (SR). In all the cases studied, lactams are more potent than the corresponding thiolactams. Activity against type 2 SR is greatly enhanced by a styryl (or azo) substituent on the aryl ring of the tri- and bicycles and also a related tricyclic aryl acid.     

Novel reverse-turn mimics inhibit farnesyl transferase

Reverse-turn inducing bicyclic lactams were incorporated into the substrate sequence recognized by farnesyl transferase to create inhibitors of RAS farnesylation. While the free peptides did not show any effect on the farnesylation, their Fmoc-protected counterparts impede the transformation of RAS with IC50's in the low micromolar range.     

Structural/mechanistic insights into the efficacy of nonclassical β‐lactamase inhibitors against extensively drug resistant Stenotrophomonas maltophilia clinical isolates

Clavulanic acid and avibactam are clinically deployed serine β‐lactamase inhibitors, important as a defence against antibacterial resistance. Bicyclic boronates are recently discovered inhibitors of serine and some metallo β‐lactamases. Here, we show that avibactam and a bicyclic boronate inhibit L2 (serine β‐lactamase) but not L1 (metallo β‐lactamase) from the extensively drug resistant human pathogen Stenotrophomonas maltophilia. X‐ray crystallography revealed that both inhibitors bind L2 by covalent attachment to the nucleophilic serine. Both inhibitors reverse ceftazidime resistance in S. maltophilia because, unlike clavulanic acid, they do not induce L1 production. Ceftazidime/inhibitor resistant mutants hyperproduce L1, but retain aztreonam/inhibitor susceptibility because aztreonam is not an L1 substrate. Importantly, avibactam, but not the bicyclic boronate is deactivated by L1 at a low rate; the utility of avibactam might be compromised by mutations that increase this deactivation rate. These data rationalize the observed clinical efficacy of ceftazidime/avibactam plus aztreonam as combination therapy for S. maltophilia infections and confirm that aztreonam‐like β‐lactams plus nonclassical β‐lactamase inhibitors, particularly avibactam‐like and bicyclic boronate compounds, have potential for treating infections caused by this most intractable of drug resistant pathogens.     

A Newer Method of the N-Acylation of Some Lactams via N-Trimethylsilyl Lactams

A newer method of the N-acylation of lactams via N-trimethylsilyl lactams is described.     

Lactam bridge stabilization of α-helical peptides: Ring size,orientation and positional effects

A series of 14 residue amphipathic α-helical peptides, in which the sidechains of glutamic acid and lysine have been covalently joined, was synthesized in order to determine the effect of spacing, position and orientation of these lactam bridges. It was found that although an (i, i+3) spacing would position the lactam bridge on the same face of the helix, these lactams with 18-member rings were actually helix-destabilizing regardless of position or location. On the other hand, (i, i+4) lactams with 21-member rings were helix-stabilizing but this was dependent on orientation. Glutamic acid-lysine lactams increased the helical content of the peptide when compared with their linear homologue in benign conditions (50 mM KH₂PO₄, 100 mM KCl, pH 7). Two Glu-Lys (i, i+4) lactams located at the N- and C-termini gave rise to a peptide with greater than 99% helical content in benign conditions. Peptides with Lys-Glu oriented lactams were random structures in benign conditions but in the presence of 50% TFE could be induced into a helical conformation. The stability of the single-stranded α-helices, as measured by thermal denaturations in 25% TFE indicated that Glu-Lys oriented lactam bridges stabilized the helical conformation relative to the linear unbridged peptide. One Glu-Lys lactam in the middle of the peptide was more effective at stabilizing helical structure than two Glu-Lys lactams positioned one at each end of the molecule. The lactams with the Lys-Glu orientation were destabilizing relative to the unbridged peptide. This study demonstrates that correct orientation and position of a lactam bridge is critical in order to design peptides with high helical content in aqueous media.     

Targeting integrins: insights into structure and activity of cyclic RGD pentapeptide mimics containing azabicycloalkane amino acids

A small library of cyclic RGD pentapeptide mimics incorporating stereoisomeric 5,6- and 5,7-fused bicyclic lactams was synthesized. This library was found to contain high-affinity ligands for the alpha(v)beta3 integrin. The aim of this study was to investigate activity, selectivity, and structure of these ligands in order to identify new specific alpha(v)-integrin antagonists that could be evaluated as tumor angiogenesis inhibitors. In vitro screening, including receptor-binding assays to purified alpha(v)beta3, alpha(v)beta5, and alpha5beta1 integrins, and platelet aggregation assay, revealed ST1646 as a potent, highly selective alpha(v)beta3/alpha(v)beta5 integrin antagonist. Structure determination of the cyclic RGD pentapeptide mimics performed by a combination of NMR spectroscopy, and molecular mechanics and dynamics calculations showed a strong dependence of the RGD cyclopeptide conformation on lactam ring size and stereochemistry. ST1646 revealed the highest ability within the library to adopt the proper RGD orientation required for binding to the alpha(v)beta3 integrin, as deduced from the recently solved crystal structure of the extracellular segment of integrin alpha(v)beta3 in complex with a cyclic pentapeptide ligand.     

Structurally designed novel furogamma lactams as inhibitors for bacterial propagations

Some novel furogamma lactams have been synthesised by one step condensation of arylaminomalonates with substituted furyl acryloyl chlorides. The annulation of substituted monocyclic gammalactams followed by cyclization produced novel tricyclic furogamma lactams. Some of these furogammalactams are found to exhibit Gram-positive and Gram-negative antibacterial activity at very high concentrations.     

Synthesis and structure of 6-amino-2,3,6-trideoxy-D-erythro-hexono-1,6-lactam and 6-amino-3,6-dideoxy-D-xylo-hexono-1,6-lactam

Solid-state conformations of 6-amino-2,3,6-trideoxy-D-erythro-hexono-1,6-lactam (3a) and 6-amino-3,6-dideoxy-D-xylo-hexono-1,6-lactam (7a) were determined using X-ray diffraction. Conformations of the compounds 3a, 7a, and their per-O-acetyl derivatives 4,5-di-O-acetyl-6-amino-2,3,6-trideoxy-D-erythro-hexono-1,6-lactam (3b) and 2,4,5-tri-O-acetyl-6-amino-3,6-dideoxy-D-xylo-hexono-1,6-lactam (7b) in solutions were deduced from the analysis of NMR spectra using a modified Karplus equation and compared with the results of circular dichroism measurement of lactams 3a and 7a. Conformation 4C(1,N) was revealed for solid lactams 3a and 7a and for lactams 7a and 7b in solution, while lactams 3a and 3b in solution exist in the approximately 1:1 equilibrium of the conformers 4C(1,N) and (1,N)C4.     

Discovery of highly selective EP4 receptor agonists that stimulate new bone formation and restore bone mass in ovariectomized rats

Heptanoic acid lactams, exemplified by 2, were identified as highly selective EP4 agonists via high throughput screening. Lead optimization led to the identification of lactams with a 30-fold increase in EP4 potency in vitro. Compounds demonstrated robust bone anabolic effects when administered in vivo in rat models of osteoporosis.     

Imide and lactam derivatives of N-benzylpyroglutamyl-L-phenylalanine as VCAM/VLA-4 antagonists

A series of imides and lactams derived from 4-amino-N-benzylpyroglutamyl-L-phenylalanine was prepared and evaluated for activity as VCAM/VLA-4 antagonists. Imides were more potent than the corresponding lactams; several had subnanomolar IC50s in an ELISA based assay and were also highly effective at blocking VLA-4 expressing Ramos cell binding to VCAM coated plates.     

N-Thiolated beta-lactam antibacterials: effects of the N-organothio substituent on anti-MRSA activity

A study on the structure-activity profiles of N-thiolated beta-lactams 1 is reported which demonstrates the importance of the N-organothio moiety on antibacterial activity. Our results indicate that elongation of the N-alkylthio residue beyond two carbons, or extensive branching within the organothio substituent, diminishes antibacterial effects. Of the derivatives we examined, the N-sec-butylthio beta-lactam derivative 5g possesses the strongest growth inhibitory activity against methicillin-resistant Staphylococcus aureus strains. Sulfur oxidation state is important, as the N-sulfenyl and N-sulfinyl groups provide for the best antibacterial activity, while lactams bearing the N-sulfonyl or N-sulfonic acid functionalities have much weaker or no anti-MRSA properties. Stereochemistry within the organothio chain does not seem to be a significant factor, although for N-sec-butylthio beta-lactams 15a-d, the 3R,4S-lactams 15c, d are more active than the 3S,4R-stereoisomers 15a, b in agar diffusion experiments. The N-methylthio lactams are the most sensitive to the presence of glutathione, followed by N-ethylthio and N-sec-butylthio lactams, which indicates that bioactivity and perhaps bacterial selectivity of the lactams may be related to the amount of organothiols in the bacterial cell. These results support the empirical model for the mechanism of action of the compounds in which the lactam transverses the bacterial membrane to deliver the organothio moiety to its cellular target.     

7-Amino-3,4-dihydro-1H-quinolin-2-one,a compound similar to the substituted coumarins,inhibits α-carbonic anhydrases without hydrolysis of the lactam ring

Abstract

7-Amino-3,4-dihydro-1H-quinolin-2-one, a compound structurally similar to coumarins, recently discovered class of inhibitors of the α-carbonic anhydrases (CAs, EC 4.2.1.1) was investigated for its interaction with all human (h) CA isoforms, hCA I-XIV. The compound was not an inhibitor of the cytosolic, widespread isoform hCA II (K_I?>?10?µM), was a weak inhibitor of hCA I, III, IV, VA, VI and XIII (K_Is in the range of 0.90–9.5?µM) but effectively inhibited the cytosolic isoform hCA VII (K_I of 480?nM) as well as the transmembrane isoforms hCA IX, XII and XIV (K_Is in the range of 16.1–510?nM). Against many CA isoforms this lactam was a better inhibitor compared to the structurally similar 4-methyl-7-aminocoumarin, but unlike this compound, the lactam ring was not hydrolyzed and the inhibition was due to the intact bicyclic amino-quinolinone scaffold. Bicyclic lactams strucurally related to coumarins are thus a new class of CA inhibitors possessing however a distinct inhibition mechanism compared to the coumarins which undergo a hydrolysis of their lactone ring for generating the enzyme inhibitory species.     

Studies on the antifungal properties of N-thiolated beta-lactams

N-thiolated beta-lactams had previously been shown to have antibacterial activity against a narrow selection of pathogenic bacteria including Staphylococcus aureus and Bacillus anthracis, as well as apoptotic-inducing activity in a variety of human cancer cell lines. We now have found that these lactams also possess antifungal activity against Candida and other fungi by exerting powerful cytostatic effects that disrupt the structural integrity of cytoplasmic membranes. The mode of action and structure-activity trends of these lactams as antifungals parallel that previously seen in our antibacterial studies.     

A novel route to synthesize Freidinger lactams by micowave irradiation.

The incorporation of a Freidinger-like lactam structure into the backbone of peptides has been proven to be an useful strategy in the design of a variety of conformationally restricted targets. Several different strategies have been developed toward Freidinger lactams but no one resulted to be completely facile. Here, we report an efficient strategy that involves the iodo-derivatives in side chain of an appropriate amino acid used as electrophilic agent, and the standard solid phase peptide synthesis assisted by microwave irradiation. The methodology developed could be useful to perform Freidinger-like lactams with defined stereochemistry for routine use in solid phase peptide chemistry.     

VCD spectroscopic investigation of enantiopure cyclic beta-lactams obtained through Lipolase-catalyzed enantioselective ring-opening reaction

A direct enzymatic method for the preparation of cyclic beta-lactams and beta-amino acids was recently developed, involving the Lipolase-catalyzed enantioselective hydrolysis of racemic beta-lactams in an organic solvent. Vibrational circular dichroism (VCD) spectroscopy combined with quantum chemical calculations at ab initio (DFT) level of theory has now been applied to determine the absolute configuration and conformation of a series of cyclic beta-lactams (1-10). The absolute configuration of 8 was derived from X-ray crystallography. Only indirect evidence was available for 1, 2, 5, 6, and 7. The absolute configuration of the new lactams 3, 4, 9, and 10 was not known previously. The VCD analysis indicated the homochirality of the studied lactams. The conformation of the flexible beta-lactams was also predicted from the VCD data. Even in the cases where multiple conformers are allowed, the predominance of one conformer was found, with the exception of 2, being present as a mixture of four conformers. Beta-lactams tend to form H-bonded dimers. The fine structure of the amide I VCD band suggested that only a small population of H-bonded dimers is formed in deuterated chloroform.     

Synthesis and potato cell expansion-inducing activity of the stereochemically restricted bicyclic analogue of 7-epi-jasmonic acid

The stereochemically restricted bicyclic analogue of 7-epi-jasmonic acid was synthesized from a known bicyclo[3.3.0]octane derivative. The enol triflate derived from the bicyclic compound was subjected to palladium-catalyzed coupling with allyltributyltin to give the desired carbon skeleton. Selective catalytic hydrogenation and subsequent acidic hydrolysis gave a new bicyclic analogue of 7-epi-jasmonic acid. The ACC conjugate of the bicyclic analogue was also synthesized. This ACC conjugate exhibited only slightly weaker potato cell expansion-inducing activity than that of the JA standard.     

Synthesis and Potato Cell Expansion-inducing Activity of the Stereochemically Restricted Bicyclic Analogue of 7-Epi-jasmonic Acid

The stereochemically restricted bicyclic analogue of 7-epi-jasmonic acid was synthesized from a known bicyclo[3.3.0]octane derivative. The enol triflate derived from the bicyclic compound was subjected to palladium-catalyzed coupling with allyltributyltin to give the desired carbon skeleton. Selective catalytic hydrogenation and subsequent acidic hydrolysis gave a new bicyclic analogue of 7-epi-jasmonic acid. The ACC conjugate of the bicyclic analogue was also synthesized. This ACC conjugate exhibited only slightly weaker potato cell expansion-inducing activity than that of the JA standard.     

Mass spectral studies on steroidal compounds-3 6-aza compounds in the cholestane series (ring B -lactams)

The mass spectra of five structurally related 6-aza compounds in the cholestane series, namely, 6-aza-B-homo-5α-cholestan-7-one(I) and its 3β-chloro-(II), 3β-bromo-(III), 3β-acetoxy-(IV) and 3-oxo-(v) analogues have been examined. These lactams show two significant cleavage modes, A and B (Formula I') which may be of diagnostic value in characterisation of such lactams. The composition of the salient fragment ions have been determined by accurate mass measurement which throws light on the probable fragmentation pathways.     

Identification of ornithine and arginine conjugates of cholic acid by mass spectrometry.

Nalpha-Cholylornithine, -arginine, and -histidine were prepared according to a method previously employed for the chemical synthesis of the monoamino acid conjugates of bile acids. The products were shown to involve the alpha amino group of the dibasic amino acids by examination of the mass spectra of the original compounds, their lactams, their methyl esters and the methyl ester acetates. Only the methyl ester acetates gave detectable amounts of molecular ion. The free acids and the methyl esters of Nalpha-cholylornithine and -arginine gave identical lactams upon sublimation from the direct insertion probe. The synthetic Nalpha-cholylarginine was shown to yield a mass spectrum identical to that of an arginocholic acid recovered from the bile of an isolated perfused rat liver.     

Aristololactams of Aristolochia argentina

Four new lactams have been isolated and characterized from the roots of Aristolochia argentina.