Structure-activity studies of normal and retro pig cecropin-melittin hybrids.

Chimeric analogs of cecropin P1 and melittin with normal and retro sequences were synthesized to explore the effect of sequence, amide bond direction (helical dipole), charge, amphipathicity and hydrophobicity on their antibacterial activity and channel-forming ability. When viewed from the opposite end by rotation in the plane 180 degrees retro analogs have the same sequence as the parent with reversed amide bond and helical dipole directions. The expected activities were related to the important structural features and a series of assumptions were made. Retro analogs are expected to be inactive if both sequence and amide bond direction make critical contributions to the activity. CP1(1-10)M(2-9) amide, (SWLSKTAKKLIGAVLKVL), showed a broad antibacterial spectrum with high activity against the two Gram-negative and three Gram-positive bacteria tested. Retro-CP1(1-10)M(2-9) was less active compared to its normal peptide. CP1(1-9)M(1-8) and CP1(1-9)M(2-8) amides were found to be active against Gram-negative Escherichia coli and also Gram-positive Streptococcus pyogenes, but inactive against the other test organisms. The corresponding retro analogs were inactive against all the five bacteria tested. These results suggest that both sequence and amide bond direction (helix dipole) are important structural requirements for the activity of CP1-M hybrids. Acetylation of the N-terminal amine in both normal and retro analogs lowered their activity, indicating the contribution of free amine to the activity. These analogs form ion-conducting channels in lipid bilayers. The action of the peptides may be explained by self-aggregation and formation of ion-conducting pores across bacterial membranes. Conformational analysis obtained from CD measurements showed that all analogs form amphipathic alpha-helices in presence of 12-20% hexafluoro isopropanol. The retro CP1(1-10)M(2-9) amide showed higher helicity and is more potent compared to other retro analogs synthesized. These studies show the effect of small sequence modifications on the biological activity of the peptides and on their alpha-helical conformation in HFIP, the structure-inducing organic solvent.     

Synthesis and antitumor activity of simplified ecteinascidin-saframycin analogs

Two series of simplified analogs of the ecteinascidin-saframycin type alkaloids were prepared from l-DOPA. Their in vitro antitumor activity was tested against three human cancer cell lines (HCT-8 colon carcinoma, Bel-7402 liver carcinoma, and BGC-823 gastric carcinoma). Among these compounds, the ester analogs have stronger activities than those of amide analogs in general. Among them, 1-naphthalene carboxylate ester analog 31 has the strongest activity against BGC-823 cells.     

Diverse amide analogs of sulindac for cancer treatment and prevention

Sulindac is a non-steroidal anti-inflammatory drug (NSAID) that has shown significant anticancer activity. Sulindac sulfide amide (1) possessing greatly reduced COX-related inhibition relative to sulindac displayed in vivo antitumor activity that was comparable to sulindac in a human colon tumor xenograft model. Inspired by these observations, a panel of diverse sulindac amide derivatives have been synthesized and their activity probed against three cancer cell lines (prostate, colon and breast). A neutral analog, compound 79 was identified with comparable potency relative to lead 1 and activity against a panel of lymphoblastic leukemia cell lines. Several new series also show good activity relative to the parent (1), including five analogs that also possess nanomolar inhibitory potencies against acute lymphoblastic leukemia cells. Several new analogs identified may serve as anticancer lead candidates for further development.     

Synthesis of a series of caffeic acid phenethyl amide (CAPA) fluorinated derivatives: Comparison of cytoprotective effects to caffeic acid phenethyl ester (CAPE)

A series of catechol ring-fluorinated derivatives of caffeic acid phenethyl amide (CAPA) were synthesized and screened for cytoprotective activity against H₂O₂ induced oxidative stress in human umbilical vein endothelial cells (HUVEC). CAPA and three fluorinated analogs were found to be significantly cytoprotective when compared to control, with no significant difference in cytoprotection between caffeic acid phenethyl ester (CAPE) and CAPA.     

Synthesis and preliminary antibacterial evaluation of simplified thiomarinol analogs

A series of simplified thiomarinol derivatives was prepared by way of catalytic enantioselective inverse electron demand hetero [4+2] cycloaddition/allylboration tandem reaction. As a preliminary evaluation, these analogs were tested for antimicrobial activity using a standard disk diffusion assay. Whereas amide analogs were less active, the simple ester analogs 3 and 4 were demonstrated to be more active than thiomarinol H.     

Heteroarylureas with fused bicyclic diamine cores as inhibitors of fatty acid amide hydrolase

A series of mechanism-based heteroaryl urea fatty acid amide hydrolase (FAAH) inhibitors with fused bicyclic diamine cores is described. In contrast to compounds built around a piperazine core, most of the fused bicyclic diamine bearing analogs prepared exhibited greater potency against rFAAH than the human enzyme. Several compounds equipotent against both species were identified and profiled in vivo.     

Structure--activity study of the antibacterial peptide fallaxin

Fallaxin is a 25-mer antibacterial peptide amide, which was recently isolated from the West Indian mountain chicken frog Leptodactylus fallax. Fallaxin has been shown to inhibit the growth of several Gram-negative bacteria including Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Here, we report a structure-activity study of fallaxin based on 65 analogs, including a complete alanine scan and a full set of N- and C-terminal truncated analogs. The fallaxin analogs were tested for hemolytic activity and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate resistant S. aureus, (VISA), methicillin-susceptible S. aureus (MSSA), E. coli, K. pneumoniae, and P. aeruginosa. We identified several analogs, which showed improved antibacterial activity compared to fallaxin. Our best candidate was FA12, which displayed MIC values of 3.12, 25, 25, and 50 muM against E. coli, K. pneumoniae, MSSA, and VISA, respectively. Furthermore, we correlated the antibacterial activity with various structural parameters such as charge, hydrophobicity H, mean hydrophobic moment mu(H), and alpha-helicity. We were able to group the active and inactive analogs according to mean hydrophobicity H and mean hydrophobic moment mu(H). Far-UV CD-spectroscopy experiments on fallaxin and several analogs in buffer, in TFE, and in membrane mimetic environments (small unilamellar vesicles) indicated that a coiled-coil conformation could be an important structural trait for antibacterial activity. This study provides data that support fallaxin analogs as promising lead structures in the development of new antibacterial agents.     

Ester- and amide-containing multiQACs: Exploring multicationic soft antimicrobial agents

Quaternary ammonium compounds (QACs) are ubiquitous antiseptics whose chemical stability is both an aid to prolonged antibacterial activity and a liability to the environment. Soft antimicrobials, such as QACs designed to decompose in relatively short times, show the promise to kill bacteria effectively but not leave a lasting footprint. We have designed and prepared 40 soft QAC compounds based on both ester and amide linkages, in a systematic study of mono-, bis-, and tris-cationic QAC species. Antimicrobial activity, red blood cell lysis, and chemical stability were assessed. Antiseptic activity was strong against a panel of six bacteria including two MRSA strains, with low micromolar activity seen in many compounds; amide analogs showed superior activity over ester analogs, with one bisQAC displaying average MIC activity of ～1 μM. For a small subset of highly bioactive compounds, hydrolysis rates in pure water as well as buffers of pH = 4, 7, and 10 were tracked by LCMS, and indicated good stability for amides while rapid hydrolysis was observed for all compounds in acidic conditions.     

The discovery of potent blockers of the canonical transient receptor channels,TRPC3 and TRPC6, based on an anilino-thiazole pharmacophore

Lead optimization of piperidine amide HTS hits, based on an anilino-thiazole core, led to the identification of analogs which displayed low nanomolar blocking activity at the canonical transient receptor channels 3 and 6 (TRPC3 & 6) based on FLIPR (carbachol stimulated) and electrophysiology (OAG stimulated) assays. In addition, the anilino-thiazole amides displayed good selectivity over other TRP channels (TRPA1, TRPV1, and TRPV4), as well as against cardiac ion channels (CaV1.2, hERG, and NaV1.5). The high oxidation potential of the aliphatic piperidine and aniline groups, as well as the lability of the thiazole amide group contributed to the high clearance observed for this class of compounds. Conversion of an isoquinoline amide to a naphthyridine amide markedly reduced clearance for the bicyclic piperidines, and improved oral bioavailability for this compound series, however TRPC3 and TRPC6 blocking activity was reduced substantially. Although the most potent anilino-thiazole amides ultimately lacked oral exposure in rodents and were not suitable for chronic dosing, analogs such as 14–19, 22, and 23 are potentially valuable in vitro tool compounds for investigating the role of TRPC3 and TRPC6 in cardiovascular disease.     

Synthesis, pharmacological evaluation and docking studies of N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs as COX-2 inhibitors

The existing NSAIDs having number of toxicities emphasises the need for discovery of new non-toxic anti-inflammatory agents. In this Letter, we present the simple two step chemical synthesis, in vivo pharmacological screening and docking study of few N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs. Different amino benzothiazoles were chloroacetylated and further reacted with substituted piperazines in presence of a base to get N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs (A1-C4). These compounds were evaluated for anti-inflammatory activity by carragenan induced paw oedema method. Promising compounds were screened for toxicity by evaluating the ulcerogenic potential. Molecular docking experiments were carried out against COX-2 enzyme using Surflex-Dock GeomX programme of Sybyl software on Dell T-1500 workstation to confirm the mechanism of action of active compounds among the series. In silico study reveal the binding interactions of N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs with COX-2 protein and is in agreement with the in vivo anti-inflammatory activity.     

Synthesis of substrates and inhibitors of botulinum neurotoxin type A metalloprotease.

Botulinum neurotoxin (BoNT) metalloproteases and related proteases are the most selective proteases known. X-ray crystal structures suggest that the active sites of the native enzymes exist in catalytically incompetent forms that must be activated by substrate binding. In order to characterize the postulated substrate-induced conformational changes for enzyme activation, we synthesized a series of transition-state analog inhibitors in which the dipeptide cleavage site is replaced by tetrahedral intermediate analogs within the minimal substrate peptide sequence. In this paper, we report our efforts to design inhibitors of BoNT/A metalloprotease. We confirm that an effective substrate sequence for BoNT/A metalloprotease is a 17-mer peptide corresponding to residues 187-203 of SNAP-25. A more stable substrate, Nle202SNAP-25 [187-203] was synthesized in order to develop an assay for proteolytic activity of BoNT/A metalloprotease that can be used to monitor time-dependent inhibition. Alpha-thiol amide analogs of Gln-197 were incorporated via solid-phase peptide synthesis into both 17-mer minimal peptide substrate sequences. The synthesis, characterization and inhibition kinetics for the alpha-thiol amide analogs of holotoxin A substrate are described. These substrate-derived inhibitors were shown to be submicromolar inhibitors of BoNT/A catalytic activity.     

Discovery of potent antimicrobial peptide analogs of Ixosin-B

Antimicrobial peptides (AMPs) represent the first defense line against infection when organisms are infected by pathogens. These peptides are generally good targets for the development of antimicrobial agents. Peptide amide analogs of Ixosin-B, an antimicrobial peptide with amino acid sequence of QLKVDLWGTRSGIQPEQHSSGKSDVRRWRSRY, were designed, synthesized and examined for antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Within the peptides synthesized, we discovered an 11-mer peptide, KRLRRVWRRWR-amide, which exhibited potent antimicrobial activity while very little hemolytic activity in human erythrocytes was observed even at high dose level (100 μM). With further modifications, this peptide could be developed into a potent antimicrobial agent in the future.     

Syntheses and studies of amamistatin B analogs reveals that anticancer activity is relatively independent of stereochemistry, ester or amide linkage and select replacement of one of the metal chelating groups

A series of analogs of the amamistatin natural products was designed and synthesized to facilitate additional anticancer structure-activity relationships. The results indicate that the anticancer activity is relatively independent of stereochemistry, ester or amide linkage and replacement of the oxazoline/oxazole based iron-binding group with a catechol.     

Antibacterial activities of temporin A analogs

Temporin A (TA) is a small, basic, highly hydrophobic, antimicrobial peptide amide (FLPLIGRVLSGIL-NH2) found in the skin of the European red frog, Rana temporaria. It has variable antibiotic activities against a broad spectrum of microorganisms, including clinically important methicillin-sensitive and -resistant Staphylococcus aureus as well as vancomycin-resistant Enterococcus faecium strains. In this investigation the antimicrobial activity and structural characteristics of TA synthetic analogs were studied. For antibacterial activity against S. aureus and enterococcal strains, the hydrophobicity of the N-terminal amino acid of TA was found to be important as well as a positive charge at amino acid position 7, and bulky hydrophobic side chains at positions 5 and 12. Replacing isoleucine with leucine at amino acid positions 5 and 12 resulted in the greatest enhancement of antibacterial activity. In addition, there was little difference between the activities of TA and its all-D enantiomer, indicating that the peptide probably exerts its effect on bacteria via non-chiral interactions with membrane lipids.     

High expression of class III β-tubulin has no impact on functional cancer cell growth inhibition of a series of key vinblastine analogs

Clinical association studies have implicated high expression of class III β-tubulin as a predictive factor for lower response rates and reduced overall survival in patients receiving tubulin binding drugs, most notably the taxanes. Because of the implications, we examined a series of key vinblastine analogs that emerged from our studies in functional cell growth inhibition assays for their sensitivity to high expression of class III β-tubulin (human non-small cell lung cancer cell line A549 vs taxol-resistant A549-T24). Unlike taxol, vinblastine and a set of key analogs 3–10 did not exhibit any loss in sensitivity toward A549-T24. The results suggest that vinblastine and related analogs are not likely prone to resistance derived from high expression of class III β-tubulin unlike the taxanes. Most significant are the results with 4–6, a subset of 20′ amide vinblastine analogs. They match or exceed the potency of vinblastine and they display more potent activity against taxol-resistant A549-T24 than even wild type A549 cells (1.2–2-fold), complementing our prior observations that they also display no sensitivity to overexpression of Pgp (HCT116/VM46 vs HCT116) and are not subject to resistance derived from Pgp efflux.     

Structure-activity relationships of precursors and analogs of natural 3-enoyl-tetramic acids

Fragments and synthetic precursors prepared en route to the macrocyclic 3-acyltetramic acids (=3-acyl-1,5-dihydro-4-hydroxy-2H-pyrrol-2-ones) aburatubolactam and macrocidin A, as well as other analogs with variance in the ring heteroatom (N, O, S), and the residues at N(1), C(3), and C(5) were tested for cytotoxic and antimicrobial effects. Anticancer activity against various tumor cell lines in vitro did not necessarily require an intact pyrrolidin-2,4-dione ring. An acyclic β-hydroxy-octatrienoyl amide precursor to aburatubolactam also exhibited distinct activity with an IC?? (120?h) value of <2.5?μM. The length of 3-oligoenoyl residues had little influence on the anticancer activity, but 3-alka-oligoenoyl tetramic acids were far more efficacious than their 3-(4-methoxycinnamoyl) congeners. N-H-3-acyltetramic acids were generally more active than their N-Me or N-Boc analogs, unless further polar groups necessitated an increased lipophilicity for sufficient uptake. Tetronic and thiotetronic acids were far less antiproliferative in cancer cells when compared with identically substituted tetramic acids.     

Influence of ring size on the cognition-enhancing activity of DM235 and MN19, two potent nootropic drugs

A series of analogs of DM235 and MN19, characterized by rings with different size, have been prepared and evaluated for their nootropic activity in the mouse passive-avoidance test. It was found that the optimal ring size for the analogs of DM235, showing endocyclic both amidic groups, is 6 or 7 atoms. For the compounds structurally related to MN19, carrying an exocyclic amide group, the piperidine ring is the moiety which gives the most interesting compounds.     

Syntheses and biological activities of sandostatin analogs containing stereochemical changes in positions 6 or 8

In a continuation of our research efforts on the design and synthesis of novel peptidomimetic structures, we have synthesized a series of sandostatin amide analogs in which stereoisomers of threonine and beta-hydroxyvaline(beta-Hyv) are employed. The analogs D-Phe1-c[Cys2-Phe3-D-Trp4-Lys5-Xaa6-Cys 7]-Xbb8-NH2 (Xaa = allo-Thr, D-allo-Thr, D-beta-Hyv, beta-Hyv, D-Thr, and Xbb = Thr or Xaa = Thr and Xbb = allo-Thr, D-allo-Thr, beta-Hyv, D-Thr) explore the effects on biological activity of stereochemical modifications and beta-methylation at positions 6 or 8. By these modifications, we examine the role of the two residues in binding to somatostatin receptors. We describe the synthesis and biological activity of these analogs. In combination with the results of the conformational analysis, this study provides new insights into the structural requirements for the binding affinity of somatostatin amide analogs to somatostatin receptors [Mattern et al., Conformational analyses of sandostatin analogs containing stereochemical changes in positions 6 or 8].     

Design and synthesis of substrate-based inhibitors of botulinum neurotoxin type B metalloprotease

Botulinum toxin (BoNT) metalloproteases and related proteases are the most selective proteases known. X-ray crystal structures suggest that the native enzymes exist in catalytically incompetent forms that must be activated by substrate binding. In order to characterize the postulated substrate-induced conformational changes, we synthesized a series of transition state analog inhibitors (TSI) in which the dipeptide cleavage site has been replaced by tetrahedral intermediate analogs within the minimal substrate peptide sequence. Reduced amide, alpha-hydroxyamide, alpha-thio-amide, and hydroxyethylamine analogs of -Gln-Phe- were incorporated via solid phase peptide synthesis into 35-mer analogs of the minimal peptide substrate sequence. The synthesis, characterization, and inhibition kinetics for four series of compounds against holotoxin BoNT/B is described. The alpha-thiol amide derivatives of the 35-mer substrate were found to inhibit BONT/B in the low micromolar range.     

Biological and conformational studies of [Val4]morphiceptin and [D-Val4]morphiceptin analogs incorporating cis-2-aminocyclopentane carboxylic acid as a peptidomimetic for proline

We report the synthesis, biological activity, and conformational analysis of tetrapeptide analogs related to [Val4]morphiceptin and [D-Val4]morphiceptin in which the proline at the second position has been replaced with cis-2-aminocyclopentane carboxylic acid (cis-2-Ac5c). Since the cis-2-Ac5c residue contains a normal amide, only the trans form has been observed about the amide bond between the first and second residues. The cis-2-Ac5c is a beta amino acid with two chiral centers resulting in two possible configurational isomers, namely (1S, 2R) and 1R, 2S) forms. The analogs containing the (1S, 2R)-Ac5c residue show activity at the mu-receptor but are inactive at the delta-receptor, resulting in a high selectivity for the mu-receptor. The (1R,2S)-Ac5c containing analogs are completely inactive at both the mu- and delta-receptors. The conformational analysis indicates that the separation of the aromatic rings of the tyrosine and phenylalanine residues, as expressed by the center-to-center distance, is 10.1-12.7 A for the preferred conformations of the bioactive analogs containing the (1S,2R)-Ac5c residue while a range of 4.8-7.0 A is observed for the preferred conformations of the inactive analogs with the (IR,2S)-Ac5c residue. A comparison of the findings from the conformational analysis and biological assays establishes the fact that a relatively large separation of the two aromatic side chains is required for the mu-opioid receptor activity of these molecules. Since the tetrapeptide amides studied in this investigation show similar biological profiles to those of the morphiceptin-related analogs, we have compared the preferred conformations estimated for the cis-2-Ac5c containing analogs with those of morphiceptin. One of the low energy conformations calculated for morphiceptin with the cis form about the tyrosine and proline residues has considerable topological similarity with the bioactive analogs containing the (1S,2R)-Ac5c residue, indicating that the cis from about these two residues is required for the biological activity of the morphiceptin-related analogs containing the proline at the second position.