Srinivasa R. Tala

Design, Synthesis, and Structure−Activity Relationship of a Novel Series of 2-Aryl 5-(4-Oxo-3-phenethyl-2-thioxothiazolidinylidenemethyl)furans as HIV-1 Entry Inhibitors⊥

We previously identified two small molecules targeting the HIV-1 gp41, N-(4-carboxy-3-hydroxy)phenyl-2,5-dimethylpyrrole 12 (NB-2) and N-(3-carboxy-4-chloro)phenylpyrrole 13 (NB-64), that inhibit HIV-1 infection at low micromolar levels. On the basis of molecular docking analysis, we designed a series of 2-aryl 5-(4-oxo-3-phenethyl-2-thioxothiazolidinylidenemethyl)furans. Compared with 12 and 13, these compounds have bigger molecular size (437-515 Da) and could occupy more space in the deep hydrophobic pocket on the gp41 NHR trimer. Fifteen 2-aryl 5-(4-oxo-3-phenethyl-2-thioxothiazolidinylidenemethyl)furans (11a-o) were synthesized by Suzuki-Miyaura cross-coupling followed by a Knoevenagel condensation and tested for their anti-HIV-1 activity and cytotoxicity on MT-2 cells. We found that all 15 compounds had improved anti-HIV-1 activity and 3 of them (11a, 11b, and 11d) exhibited inhibitory activity against replication of HIV-1(IIIB) and 94UG103 at <100 nM range, more than 20-fold more potent than 12 and 13, suggesting that these compounds can serve as leads for development of novel small molecule HIV fusion inhibitors.

Design, Synthesis, and Biological Activity of Novel 5-((Arylfuran/1H-pyrrol-2-yl)methylene)-2-thioxo-3-(3-(trifluoromethyl)phenyl)thiazolidin-4-ones as HIV-1 Fusion Inhibitors Targeting gp41

On the basis of our earlier molecular docking analysis, we designed and synthesized 5-((arylfuran/1H-pyrrol-2-yl)methylene)-2-thioxo-3-(3-(trifluoromethyl)phenyl)thiazolidin-4-ones (12a-o) as HIV-1 entry inhibitors. Compounds 12a-o effectively inhibited infection by both laboratory-adapted and primary HIV-1 strains and blocked HIV-1 mediated cell-cell fusion and gp41 six-helix bundle formation. Molecular docking analyses on two highly active inhibitors, 12b, containing a carboxylic acid group, and 12m, containing a tetrazole group, indicated that they both fit snugly into the hydrophobic cavity of HIV-1 gp41 from which each has important ionic interactions with lysine 574 (K574). By contrast, molecular docking of 12i, a less active compound containing a pyrrole instead of a furan ring, indicated a completely different orientation from 12b and 12m and missed critical interactions.

Selective synthesis and structural elucidation of S-acyl- and N-acylcysteines.

N-(Acyl)-1H-benzotriazoles 6a-f react with l-cysteine 5 at 20 degrees C to give exclusively (i) N-acyl-l-cysteines 8a-e in the presence of triethylamine in CH(3)CN-H(2)O (3:1), but (ii) S-acyl-l-cysteines 7a-e in CH(3)CN-H(2)O (5:1) in the absence of base. Structures 7b, 7d and 8b, 8d are supported by 2D NMR spectroscopic methods including gDQCOSY, gHMQC, gHMBC, and (1)H-(15)N CIGAR-gHMBC experiments. The structure of compound 8d was also supported by single-crystal X-ray diffraction.

The chemical ligation of selectively S-acylated cysteine peptides to form native peptides via 5-, 11- and 14-membered cyclic transition states

Cysteine and C-terminal cysteine peptides are selectively S-acylated at 0-20 degrees C by N-(Pg-alpha-aminoacyl)benzotriazoles to give N-Pg-S-acyl-isodi-, -isotri-, and -isotetra-peptides isolated in good yields. N-Fmoc-S-acyl-isopeptides are Fmoc deprotected to afford free S-acyl-isopeptides isolated in high yields. S-Acyl-isodi-, S-acyl-isotetra-, and S-acyl-isopentapeptides undergo chemical ligation; migration of the cysteine S-acyl groups to the N-terminal amino acids via 5-, 11-, and 14-membered transition states giving the corresponding native di-, tetra-, and penta-peptides. By contrast, the Sacyl-isotripeptide prefers intermolecular acylation from one molecule to another over an 8-membered intramolecular transition state. The developed methodology allows convenient isolation of stable, unprotected S-acyl cysteine peptides including the first isolation of S-acyl-isopeptides, which should facilitate the investigation of ligation by physical organic chemistry techniques.

QSAR modeling, synthesis and bioassay of diverse leukemia RPMI-8226 cell line active agents

A rigorous QSAR modeling procedure employing CODESSA PRO descriptors has been utilized for the prediction of more efficient anti-leukemia agents. Experimental data concerning the effect on leukemia RPMI-8226 cell line tumor growth of 34 compounds (treated at a dose of 10 μM) was related to their chemical structures by a 4-descriptor QSAR model. Four bis(oxy)bis-urea and bis(sulfanediyl)bis-urea derivatives (4a, 4b, 8, 11a) predicted as active by this model, together with 11b predicted to be of low activity, were synthesized and screened for anti-tumor activity utilizing 55 different tumor cell lines. Compounds 8 and 11a showed anti-tumor properties against most of the adopted cell lines with growth inhibition exceeding 50%. The highly promising preliminary anti-tumor properties of compounds 8 and 11a, were screened at serial dilutions (10(-4)-10(-8) μM) for determination of their GI(50) and TGI against the screened human tumor cell lines. Compound 11a (GI(50) = 1.55, TGI = 8.68 μM) is more effective than compound 8 (GI(50)=58.30, TGI = > 100 μM) against the target leukemia RPMI-8226 cell line. Compound 11a also exhibits highly pronounced anti-tumor properties against NCI-H226, NCI-H23 (non-small cell lung cancer), COLO 205 (colon cancer), SNB-75 (CNS cancer), OVCAR-3, SK-OV-3 (ovarian cancer), A498 (renal cancer) MDA-MB-231/ATCC and MDA-MB-468 (breast cancer) cell lines (GI(50) = 1.95, 1.61, 1.38, 1.56, 1.30, 1.98, 1.18, 1.85, 1.08, TGI = 8.35, 6.01, 2.67, 8.59, 4.01, 7.01, 5.62, 6.38, 5.63 μM, respectively). Thus 11a could be a suitable lead towards the design of broad spectrum anti-tumor active agents targeting various human tumor cell lines.

Benzotriazole-mediated syntheses of depsipeptides and oligoesters.

Reactions of O-Pg(α-hydroxyacyl)benzotriazoles with (a) unprotected α-hydroxycarboxylic acids, (b) amino acids, and (c) amines afforded, respectively, chirally pure (a) oligoesters, (b) depsidipeptides, and (c) amide conjugates (yields 52-94%). N-Pg(α-Aminoacyl)benzotriazoles reacted with α-hydroxycarboxylic acids to yield depsidipeptides (47-87%). N-Pg(depsidipeptidoyl)benzotriazoles, obtained from depsidipeptides, gave depsitripeptides (yields 55-78%) on reaction with amino acids and α-hydroxycarboxylic acids. O-Acylation of α-hydroxycarboxylic acids with N-Pg(α-aminoacyl)benzotriazoles followed by deprotection produced unprotected depsides useful for the preparation of depsitripeptides.

Design, synthesis, and biological activity of a novel series of 2,5-disubstituted furans/pyrroles as HIV-1 fusion inhibitors targeting gp41

Based on molecular docking analysis of earlier results, we designed a series of 2,5-disubstituted furans/pyrroles (5a-h) as HIV-1 entry inhibitors. Compounds were synthesized by Suzuki-Miyaura cross coupling, followed by a Knoevenagel condensation or Wittig reaction. Four of these compounds were found to be effective in inhibiting HIV-1 infection, with the best compounds being 5f and 5h, which exhibited significant inhibition on HIV-1(IIIB) infection at micromolar levels with low cytotoxicity. These compounds are also effective in blocking HIV-1 mediated cell-cell fusion and the gp41 six-helix bundle formation, suggesting that they are also HIV-1 fusion inhibitors targeting gp41 and have potential to be developed as a new class of anti-HIV-1 agents.

Computer-assisted rational design, synthesis, and bioassay of non-steroidal anti-inflammatory agents

A focused dataset of previously synthesized and tested [1,2,4]-triazolo[1,5-a]pyridines and pyridine-3-carboxylates was studied by Molecular Field Topology Analysis (MFTA) to identify steric and electronic determinants of anti-inflammatory activity useful for the design and synthesis of new anti-inflammatory agents. Rational design based on the MFTA model identified eleven novel pyridine-3-carboxylates (2a-e and 3a-f) as promising. After synthesis and screening, three of (2a, 2c, 3a) revealed potent anti-inflammatory activity exceeding that of indomethacin, the reference inhibitor for artificially induced edema in rats.

Convenient preparations of azo-dye labeled amino acids and amines

N-(4-Arylazobenzoyl)-1H-benzotriazoles 3 react with amino acids 4 and amines 6 to give azo-dye labeled amino acids (5a-m) and amines (7a-n) in high yields (74-100%) with retention of chirality.

Synthesis and Pharmacology of α/β3-Peptides Based on the Melanocortin Agonist Ac-His-dPhe-Arg-Trp-NH2 Sequence

The melanocortin-3 and -4 receptors are expressed in the brain and play key roles in regulating feeding behavior, metabolism, and energy homeostasis. In the present study, incorporation of β(3)-amino acids into a melanocortin tetrapeptide template was investigated. Four linear α/β(3)-hybrid tetrapeptides were designed with the modifications at the Phe, Arg, and Trp residues in the agonist sequence Ac-His-dPhe-Arg-Trp-NH2. The most potent mouse melanocortin-4 receptor (mMC4R) agonist, Ac-His-dPhe-Arg-β(3)hTrp-NH2 (8) showed 35-fold selectivity versus the mMC3R. The study presented here has identified a new template with heterogeneous backbone for designing potent and selective melanocortin receptor ligands.