Acetyl analogs of combretastatin A-4: synthesis and biological studies

The combretastatins have received significant attention because of their simple chemical structures, excellent antitumor efficacy and novel antivascular mechanisms of action. Herein, we report the synthesis of 20 novel acetyl analogs of CA-4 (1), synthesized from 3,4,5-trimethoxyphenylacetone that comprises the A ring of CA-4 with different aromatic aldehydes as the B ring. Molecular modeling studies indicate that these new compounds possess a 'twisted' conformation similar to CA-4. The new analogs effectively inhibit the growth of human and murine cancer cells. The most potent compounds 6k, 6s and 6t, have IC(50) values in the sub-μM range. Analog 6t has an IC(50) of 182 nM in MDA-MB-435 cells and has advantages over earlier analogs due to its enhanced water solubility (456 μM). This compound initiates microtubule depolymerization with an EC(50) value of 1.8 μM in A-10 cells. In a murine L1210 syngeneic tumor model 6t had antitumor activity and no apparent toxicity.     

Nucleic acid components and their analogs: Design and synthesis of novel cytosine thioglycoside analogs

The synthesis of a new category of novel cytosine 4-thioglycoside analogs has been first accomplished. The main step of this strategy is the synthesis of sodium pyrimidine-4-thiolate through the condensation of 2-cyano-N-arylacetamides with sodium cyanocarbonimidodithioate, followed by coupling with α-bromo-sugars to afford the corresponding cytosine 4-thioglycoside analogs. The free thioglycosides were also prepared. Subsequent studies on the application of this strategy for the preparation of other potent pyrimidine thioglycosides are reported.     

Synthesis and antiproliferative activity of imidazole and imidazoline analogs for melanoma

We have previously reported substituted 2-aryl-thiazolidine-4-carboxylic acid amides as potent and selective antiproliferative agents for melanoma. To understand the importance of the thiazolidine ring and to reduce potential complications associated with the two chiral centers, we designed and synthesized sets of new analogs by modifying this ring. These new analogs were tested in two melanoma cell lines and fibroblast cells (negative controls). Compared with the older analogs containing the thiazolidine ring, these new analogs have lower potency in general, but some of these analogs still have very good selectivity. These structure-activity studies indicated that the thiazolidine ring is very critical for the activity for these series of compounds.     

Exploring tryptamine conjugates as pronucleotides of phosphate-modified 7-methylguanine nucleotides targeting cap-dependent translation

Eukaryotic translation initiation factor 4E (eIF4E) is overexpressed in many cancers deregulating translational control of the cell cycle. mRNA 5′ cap analogs targeting eIF4E are small molecules with the potential to counteract elevated levels of eIF4E in cancer cells. However, the practical utility of typical cap analogs is limited because of their reduced cell membrane permeability. Transforming the active analogs into their pronucleotide derivatives is a promising approach to overcome this obstacle. 7-Benzylguanosine monophosphate (bn⁷GMP) is a cap analog that has been successfully transformed into a cell-penetrating pronucleotide by conjugation of the phosphate moiety with tryptamine. In this work, we explored whether a similar strategy is applicable to other cap analogs, particularly phosphate-modified 7-methylguanine nucleotides. We report the synthesis of six new tryptamine conjugates containing N⁷-methylguanosine mono- and diphosphate and their analogs modified with thiophosphate moiety. These new potential pronucleotides and the expected products of their activation were characterized by biophysical and biochemical methods to determine their affinity towards eIF4E, their ability to inhibit translation in vitro, their susceptibility to enzymatic degradation and their turnover in cell extract. The results suggest that compounds containing the thiophosphate moiety may act as pronucleotides that release low but sustainable concentrations of 7-methylguanosine 5′-phosphorothioate (m⁷GMPS), which is a translation inhibitor with in vitro potency higher than bn⁷GMP.     

In vitro and in vivo evaluation of select kahalalide F analogs with antitumor and antifungal activities

Kahalalide F (KF) and the regioisomer isoKF are novel anticancer drugs of marine origin and currently under clinical investigation. Here we report the synthesis of two new KF analogs with significant in vitro and in vivo antifungal and antitumor activities. The primary amine hydrogen of ornithine in KF has been replaced with 4-fluoro-3-methylbenzyl and morpholin-4-yl-benzyl via reductive N-alkylation. The TGI of these analogs using the NCI-60 cell line screening revealed promising results when compared to paclitaxel. The result of in vivo hollow fiber and animal toxicity assays are presented.     

Antimetabolites: A First Synthesis of a New Class of Cytosine Thioglycoside Analogs

A first synthesis of a new class of novel cytosine thioglycoside analogs from readily available starting materials has been described. The key step of this protocol is the formation of sodium pyrimidine-4-thiolate via condensation of N′-arylidene-2-cyanoacetohydrazides with sodium cyanocarbonimidodithioate salt, followed by coupling with halo sugars to give the corresponding cytosine thioglycoside analogs. Ammonolysis of the latter compounds afforded the free thioglycosides.     

Synthesis and antiviral evaluation of novel heteroarylpyrimidines analogs as HBV capsid effectors

New modifications to the scaffold of previously reported HBV capsid assembly effectors such as BAY 41-4109, HAP-12 and GLS4 were explored. The anti-HBV activity in the HepAD38 system, and cytotoxicity profiles of each of the new compounds has been assessed. Among them, five new iodo- and bromo-heteroarylpyrimidines analogs displayed anti-HBV activity in the low micromolar range.     

New photoaffinity analogs of paclitaxel.

Two new photoreactive paclitaxel analogs bearing [3H2]-3-(4-benzoyl)phenylpropanoyl group as the photophore as well as radiolabeling unit at the 7 and 10 positions, respectively, are developed. These new photoreactive analogs showed excellent preliminary results on the photoaffinity labeling of tubulin and P-glycoprotein.     

Synthesis of novel bicyclo[4.1.0]heptane and bicyclo[3.1.0]hexane derivatives as melanin-concentrating hormone receptor R1 antagonists

To address the hERG liability of MCHR1 antagonists such as 1 and 2, new analogs such as 4 and 5 that incorporated a polar heteroaryl group were designed and synthesized. Biological evaluation confirmed that these new analogs retained MCH R1 activity with greatly attenuated hERG liabilities as indicated in the Rb efflux assay.     

Effects of the substitution of photoreactive groups in positions 4 and 8 of vasopressin

In an effort to synthesize potent vasopressin analogs containing photoreactive groups, we prepared, by solid phase synthesis, three analogs with proline or hydroxyproline substitutions in positions 4 and/or 7, lysine in positions 4 or 8, and beta-mercaptopropionic acid in position 1. From these three parent analogs, 1-desamino[4-proline,8-lysine]VP, 1-desamino[4-hydroxyproline,8-lysine]VP, and 1-desamino[4-lysine,7-hydroxyproline]AVP, we then prepared the corresponding azido compounds using the epsilon-amino group of lysine as the attachment point. These six analogs were then assayed for antidiuretic and pressor activities in rats. One of the resulting analogs, 1-desamino[4-lysine(N epsilon-4-azidobenzoyl),7-hydroxyproline)]AVP has the highest antidiuretic activity of any photoreactive compound reported to date.     

Design of biologically active, conformationally constrained GnRH antagonists

The introduction of conformational constraints into a flexible peptide hormone can be exploited to develop models for the conformation required for receptor binding and activity. In this review, we illustrate this approach to analog design using our work on antagonists of gonadotropin-releasing hormone (GnRH). Design of a conformationally constrained, competitive antagonist of GnRH, cyclo[delta 3,4 Pro-D4ClPhe-DTrp-Ser-Tyr-DTrp-NMeLeu-Arg-Pro-bet a Ala] led to the prediction of its bioactive conformation. Template forcing experiments show that this conformation is accessible to other active GnRH analogs. Two-dimensional NMR studies verified the predicted conformation in solution. The predicted binding conformation has recently been used to design two new analogs incorporating side chain-side chain linkages suggested by the conformational model: Ac-delta 3,4Pro-D4FPhe-DTrp-Dap-Tyr-DTrp-Leu-Arg-Asp-Gly- NH2 and Ac-delta 3,4Pro-D4FPhe-DTrp-Dap-Tyr-D2Nal-Leu-Arg-Pro-Asp -NH2. These analogs were synthesized and the one predicted to be most similar to the parent conformation had equivalent potency while the second, designed to refine the conformational hypothesis, was found to exhibit enhanced potency, thus confirming the original binding conformation hypothesis. These compounds and their derivatives now provide a new class of GnRH antagonists possessing both high biological potency and limited conformational flexibility, thus making them ideal for both biophysical and structure-activity studies.     

Design and synthesis of benzo-lipoxin A4 analogs with enhanced stability and potent anti-inflammatory properties

A new class of chemically and metabolically stable lipoxin analogs featuring a replacement of the tetraene unit of native LXA(4) with a substituted benzo-fused ring system have been designed and studied. These molecules were readily synthesized via a convergent synthetic route involving iterative palladium-mediated cross-coupling, and exhibit enhanced chemical stability, as well as resistance to metabolic inactivation via eicosanoid oxido-reductase. These new LX analogs were evaluated in a model of acute inflammation and were shown to exhibit potent anti-inflammatory properties, significantly decreasing neutrophil infiltration in vivo. The most potent among these was compound 9 (o-[9,12]-benzo-15-epi-LXA(4) methyl ester. Taken together, these findings help identify a new class of stable and easily prepared LX analogs that may serve as novel tools and as promising leads for new anti-inflammatory agents with improved therapeutic profile.     

Molecular modeling, design, synthesis, and biological evaluation of novel 3',4'-dicamphanoyl-(+)-cis-khellactone (DCK) analogs as potent anti-HIV agents

Our current studies aimed at developing new potential anti-AIDS drug candidates have focused on the design and synthesis of new DCK analogs with improved molecular water solubility. Based on the structures and biodata of previous DCK analogs, 3D-QSAR studies have been performed which resulted in two reliable computational models, CoMFA and CoMSIA, with r(2) values of 0.995 and 0.987, and q(2) values of 0.662 and 0.657, respectively. In accord with these 3D-QSAR models, 15 new DCK analogs with polar functional groups at the 3-position were subsequently designed, synthesized, and evaluated against HIV-1 replication in H9 and MT4 cell lines. New DCK analogs 3b, 3c, 4b, 4c, 6a, 7c, and 9a showed promising potency with EC(50) values ranging from 0.09 to 0.0002 microM in both assays. Meanwhile, these promising compounds also showed a wide range of predicted logP values from 0.90 to 5.19, which increased the probability of identifying anti-HIV drug candidates from this class of compounds for clinical trials. Furthermore, both experimental and predicted values matched well, corroborating the reliability of the established 3D-QSAR models.     

5-((4-Aminopiperidin-1-yl)methyl)pyrrolotriazine dual inhibitors of EGFR and HER2 protein tyrosine kinases

Pyrrolotriazine dual EGFR/HER2 kinase inhibitors with a 5-((4-aminopiperidin-1-yl)methyl) solubilizing group were found to be superior to analogs with previously reported C-5 solubilizing groups. New synthetic methodology was developed for the parallel synthesis of C-4 analogs with the new solubilizing group. Interesting new leads were evaluated in tumor xenograft models and the C-4 aminofluorobenzylindazole, 1c, was found to exhibit the best antitumor activity. It is hypothesized that this solubilizing group extends into the ribose-phosphate portion of the ATP binding pocket and enhances the binding affinity of the inhibitor.     

Highly antiproliferative, low-calcemic, side-chain amide and hydroxamate analogs of the hormone 1alpha,25-dihydroxyvitamin D3

Four new side-chain amide (2 and 3) and hydroxamate (4 and 5) analogs of the hormone calcitriol (1) have been prepared. Even though lacking the 25-OH group characteristic of natural calcitriol (1), analogs 2-4 are as antiproliferative in vitro as calcitriol (1) but are 20-40 times less calciuric in vivo than calcitriol (1).     

Conformationally constrained analogs of BAY 59-3074 as novel cannabinoid receptor ligands

To obtain information on the pharmacophoric requirements of the CB1/CB2 partial agonist BAY 59-3074 we have synthesized a series of new conformationally constrained dibenzofuran (4a-d) and dibenzopyran analogs (5). All constrained analogs exhibited reduced binding affinity at both cannabinoid receptor subtypes, suggesting that planar conformations of these ligands are less favored by both receptors. We also found that 4c, 4d, and 5 exhibited 3- to 12-fold selectivity for hCB2 over rCB1 receptors and may serve as new chemotypes for the development of CB2-selective cannabinergics.     

Synthesis and biochemical properties of novel mRNA 5' cap analogs resistant to enzymatic hydrolysis

A series of new dinucleotide cap analogs with methylene groups replacing oxygens within the pyrophosphate moieties have been synthesized. All the compounds were resistant to the human scavenger decapping hydrolase, DcpS. Binding constants of the modified caps to eIF4E are comparable to those obtained for m7GpppG. This suggests these methylene modifications in the pyrophosphate chain do not significantly affect cap-binding at least for eIF4E. These cap analogs are also good inhibitors of in vitro translation. mRNAs capped with novel analogs were translated similarly to the mRNA capped with the parent m7GpppG.     

Pseudopeptides containing the 2-hydrazonoacyl fragment: analogs of the chemotactic agent HCO-Met-Leu-Phe-OMe.

In order to further examine the properties of pseudopeptides containing the 2-hydrazonoacyl fragment, two new series of analogs of the prototypical chemotactic N-formyl-tripeptide HCO-Met-Leu-Phe-OMe were designed and synthesized. The first group contains the new fragment as the N-terminal residue and is represented by the N-aryl derivatives p-Cl-C6H4-NH-N=C(R)-CO-Leu-Phe-OMe (2 and 3) and by the corresponding N-aroyl analogs p-CH3-C6H4-CO-NH-N=C(R)-CO-Leu-Phe-OMe (4). The second group contains the new fragment in place of the central Leu residue and is represented by compounds HCO-Xaa-NH-N=C(R)-CO-Phe-OMe (7a and 7b) where Xaa is Nle and Met, respectively. The conformational and biochemical properties of the new products were examined.     

New Combretastatin Analogs as Anticancer Agents: Design,Synthesis, Microtubules Polymerization Inhibition,and Molecular Docking Studies

A new series of 4-(4-methoxyphenyl)-5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazole-3-thiol derivatives were synthesized as analogs for the anticancer drug combretastatin A-4 ( CA-4 ) and characterized using FT-IR, ¹H-NMR, ¹³CNMR, and HR-MS techniques. The new CA-4 analogs were designed to meet the structural requirements of the highest expected anticancer activity of CA-4 analogs by maintaining ring A 3,4,5-trimethoxyphenyl moiety, and at the same time varying the substituents effect of the triazole moiety (ring B ). In silico analysis indicated that compound 3 has higher total energy and dipole moment than colchicine and the other analogs, and it has excellent distribution of electron density and is more stable, resulting in an increased binding affinity during tubulin inhibition. Additionally, compound 3 was found to interact with three apoptotic markers, namely p53, Bcl-2, and caspase 3. Compound 3 showed strong similarity to colchicine , and it has excellent pharmacokinetics properties and a good dynamic profile. The in vitro anti-proliferation studies showed that compound 3 is the most cytotoxic CA-4 analog against cancer cells (IC₅₀ of 6.35 μM against Hep G2 hepatocarcinoma cells), and based on its selectivity index (4.7), compound 3 is a cancer cytotoxic-selective agent. As expected and similar to colchicine , compound 3 -treated Hep G2 hepatocarcinoma cells were arrested at the G2/M phase resulting in induction of apoptosis. Compound 3 tubulin polymerization IC₅₀ (9.50 μM) and effect on V_max of tubulin polymerization was comparable to that of colchicine (5.49 μM). Taken together, the findings of the current study suggest that compound 3 , through its binding to the colchicine-binding site at β-tubulin, is a promising microtubule-disrupting agent with excellent potential to be used as cancer therapeutic agent.     

Synthesis, conformation and biology of naphthoxylosides

Proteoglycans (PG) are polyanionic proteins consisting of a core protein substituted with carbohydrate chains, that is, glycosaminoglycans (GAG). The biosynthesis of GAG can be manipulated by simple xylosides carrying hydrophobic aglycons, which can enter the cell and initiate the biosynthesis. While the importance of the aglycon is well investigated, there is far less information on the effect of modifications in the xylose residue. We have developed a new synthetic protocol, based on acetal protection and selective benzylation, for modification of the three hydroxyl groups in xylose. Thus we have synthesized twelve analogs of 2-naphthyl β-d-xylopyranoside (XylNap), where each hydroxyl group has been epimerized or replaced by methoxy, fluoro, or hydrogen. To gain more information about the properties of xylose, conformational studies were made on some of the analogs. It was found that the (4)C(1) conformation is highly predominant, accompanied by a nonnegligible population of the (2)S(0) conformation. However, deoxygenation at C3 results in a large portion of the (1)C(4) conformation. The GAG priming ability and proliferation activity of the twelve analogs, were investigated using a matched pair of human breast fibroblasts and human breast carcinoma cells. None of the analogs initiated the biosynthesis of GAG, but an inhibitory effect on endogenous PG production was observed for analogs fluorinated or deoxygenated at C4. From our data it seems reasonable that all three hydroxyl groups in XylNap are essential for the priming of GAG chains and for selective toxicity for tumor cells.