D-piece modifications of the hemiasterlin analog HTI-286 produce potent tubulin inhibitors

Modifications of the D-piece carboxylic acid group of the hemiasterlin analog HTI-286 gave tubulin inhibitors which were potent cytotoxic agents in taxol resistant cell lines expressing P-glycoprotein. Amides derived from proline had potency comparable to HTI-286. Reduction of the carboxylic acid to ketones and alcohols or its conversion to acidic heterocycles also gave potent analogs. Synthetic modifications of the carboxylic acid could be carried out selectively using a wide range of synthetic reagents. Proline analog 3 was found to be effective in a human xenograft model in athymic mice.     

Beta-endorphin. Synthesis and biological activity of analogs with disulfide bridges

Two analogs of human beta-endorphin (beta-EP) which contain cystine bridges, [Cys15-Cys26,Phe27,Gly31]-beta-EP (I) and [Cys16-Cys26,Phe27,Gly31]-beta-EP (II), were synthesized by the solid-phase method. Peptides I and II were shown to contain 2-2.5 times the opiate receptor binding activity of beta-endorphin. We also synthesized two analogs with reduced alkylated cysteine residues and these peptides, [Arg9,19,24,28,29 Cys(Cam)11,26,Phe27,Gly31] and [Arg9,19,24,28,29,Cys-(Cam)12,26,Phe27,Gly31], were shown to have approximately the same opiate receptor activity as beta-endorphin.     

Absolute configurations of tubulin inhibitors taltobulin (HTI-286) and HTI-042 characterized by X-ray diffraction analysis and NMR studies

The stereochemistry of the tubulin inhibitors taltobulin HTI-286 (2) and HTI-042 (3) was determined by utilizing the DPFGSE 1D NOE experiment. Single crystal X-ray diffraction analysis further confirmed the absolute configuration of these two compounds, which carry the (S,S,S)-configuration necessary for biological activity.     

Antiplasmodial activity of hydroxyethylamine analogs: Synthesis,biological activity and structure activity relationship of plasmepsin inhibitors

Malaria, particularly in endemic countries remains a threat to the human health and is the leading the cause of mortality in the tropical and sub-tropical areas. Herein, we explored new C₂ symmetric hydroxyethylamine analogs as the potential inhibitors of Plasmodium falciparum (P. falciparum; 3D7) in in-vitro cultures. All the listed compounds were also evaluated against crucial drug targets, plasmepsin II (Plm II) and IV (Plm IV), enzymes found in the digestive vacuole of the P. falciparum. Analog 10f showed inhibitory activities against both the enzymes Plm II and Plm IV (K_i, 1.93?±?0.29?µM for Plm II; K_i, 1.99?±?0.05?µM for Plm IV). Among all these analogs, compounds 10g selectively inhibited the activity of Plm IV (K_i, 0.84?±?0.08?µM). In the in vitro screening assay, the growth inhibition of P. falciparum by both the analogs (IC₅₀, 2.27?±?0.95?µM for 10f; IC₅₀, 3.11?±?0.65?µM for 10g) displayed marked killing effect. A significant growth inhibition of the P. falciparum was displayed by analog 12c with IC₅₀ value of 1.35?±?0.85?µM, however, it did not show inhibitory activity against either Plms. The hemolytic assay suggested that the active compounds selectively inhibit the growth of the parasite. Further, potent analogs (10f and 12c) were evaluated for their cytotoxicity towards mammalian HepG2 and vero cells. The selectivity index (SI) values were noticed greater than 10 for both the analogs that suggested their poor toxicity. The present study indicates these analogs as putative lead structures and could serve as crucial for the development of new drug molecules.     

Synthesis and biological activity of position 1 analogs of LH-RH.

(Formyl-sarcosine)1-LH-RH (I), (acetyl-sarcosine)1-LH-RH (II), (2-pyrrolidone-4-carboxylic acid)1-LH-RH (III), (N-methyl-2-pyrrolidone-4-carboxylic acid)1-LH-RH (IV, hydroxyproline1-LH-RH (V) and (cylcopentane-carboxylic acid)1-LH-RH (VI) were synthesized by solid phase methods on a benzhydrylamine resin support. Peptides I-IV were assayed for LH- and FSH-releasing activity over a 4-h period after subcutaneous infection into immature male rats in order to detect any prolongation ofactivity. The peptides were found to have the following integrated LH-releasing activities compared with LH-RH: I, 64%; II, 72%; III, 19%; IV, 58%. None of the peptides were found to be longer acting than LH-RH. Peptides V and VI were far less active, 0.001% and 1.4%, respectively.     

Fluorescent analogs of peptoid-based HDAC inhibitors: Synthesis,biological activity and cellular uptake kinetics

Fluorescent tagging of bioactive molecules is a powerful tool to study cellular uptake kinetics and is considered as an attractive alternative to radioligands. In this study, we developed fluorescent histone deacetylase (HDAC) inhibitors and investigated their biological activity and cellular uptake kinetics. Our approach was to introduce a dansyl group as a fluorophore in the solvent-exposed cap region of the HDAC inhibitor pharmacophore model. Three novel fluorescent HDAC inhibitors were synthesized utilizing efficient submonomer protocols followed by the introduction of a hydroxamic acid or 2-aminoanilide moiety as zinc-binding group. All compounds were tested for their inhibition of selected HDAC isoforms, and docking studies were subsequently performed to rationalize the observed selectivity profiles. All HDAC inhibitors were further screened in proliferation assays in the esophageal adenocarcinoma cell lines OE33 and OE19. Compound 2, 6-((N-(2-(benzylamino)-2-oxoethyl)-5-(dimethylamino)naphthalene)-1-sulfonamido)-N-hydroxyhexanamide, displayed the highest HDAC inhibitory capacity as well as the strongest anti-proliferative activity. Fluorescence microscopy studies revealed that compound 2 showed the fastest uptake kinetic and reached the highest absolute fluorescence intensity of all compounds. Hence, the rapid and increased cellular uptake of 2 might contribute to its potent anti-proliferative properties.     

Synthesis and biological activity of glycosylated analogs of somatostatin

The synthesis by solid-phase methodology of two glycosylated analogs of somatostatin [Glc-Asn⁵]-SS and [NAcGlc-Asn⁵]-SS is described. These two analogs have been biologically tested on the secretion of pituitary growth hormone, pancreatic glucagon and insulin. The results show that glycosylation of somatostatin on the Asn⁵ residue decreases by a hundred fold the inhibition activity on GH release when tested $\text{in}$$\text{vitro}$. $\text{In}$$\text{vivo}$, since the activity is similar to somatostatin the carbohydrates are probably removed by some enzymatic reaction and thus liberate the full activity of somatostatin.     

Synthesis and biological activity of cyclic analogs of angiotensin

Biological properties of five novel angiotensin analogues synthesized, using the conventional methods of peptide chemistry, have been studied. Cyclization was attained by means of amide linkage with the aid of diphenylphosphorylazide or pentafluorophenyl esters. Unlike the natural hormone, the cyclic analogues of angiotensin show no pressor activity, but elicit a depressor effect untypical of angiotensin. A slight pressor activity was exhibited by the compound containing aspartic acid in position 1. The cyclic analogues in question release histamine from peritoneal mast cells in rats.     

Biophysical characterization of the interactions of HTI-286 with tubulin heterodimer and microtubules

HTI-286 is a synthetic analogue of the natural product hemiasterlin and is a potent antimitotic agent. HTI-286 inhibits the proliferation of tumor cells during mitosis. The observed antimitotic activity is due to the binding of HTI-286 to tubulin. This report details the effects of HTI-286 on soluble tubulin and preassembled microtubules. HTI-286 binds tubulin monomer and oligomerizes it to an 18.5 S species corresponding to a discrete ring structure consisting of about 13 tubulin units as determined by sedimentation equilibrium analyses. The rate of formation of the oligomers is dependent on the concentration of HTI-286 and the time of incubation. Tubulin oligomers, specifically the 18.5 S species, form slowly. The interactions of HTI-286 with tubulin were studied by isothermal titration calorimetry. HTI-286 binds tubulin rapidly, and the initial association of HTI-286 with tubulin is enthalpically driven with a DeltaH value of -14 kcal/mol at 25 degrees C and a dissociation constant of ca. 100 nM. However, the accompanying tubulin oligomerization event does not produce measurable heats at 25 degrees C. The dissociation constant estimated from the changes in the intrinsic fluorescence of tubulin was found to be consistent with the calorimetric results. Both HTI-286 and hemiasterlin bind tubulin with nearly equal potency. However, the stability of the tubulin oligomers is not identical under size-exclusion column chromatographic conditions. The tubulin oligomers formed in the presence of HTI-286 dissociate on the column, while the corresponding oligomers formed in the presence of hemiasterlin are stable. Tubulin undergoes a change in the secondary structure in the presence of HTI-286, which is evidenced by changes in the circular dichroic absorption spectrum of tubulin. In contrast to the microtubule-stabilizing effects of paclitaxel, both HTI-286 and hemiasterlin depolymerize preassembled microtubules at micromolar concentrations.     

Dinucleoside polyphosphate NAD analogs as potential NMN adenylyltransferase inhibitors. Synthesis and biological evaluation

Two dinucleoside polyphosphate NAD analogs, P1-(adenosine-5')-P3-(nicotinamide riboside-5')triphosphate (Np3A, 1) and P1-(adenosine-5')-P4-(nicotinamide riboside-5')tetraphosphate (Np4A, 2), were synthesized and tested as inhibitors of both microbial and human recombinant NMN adenylyltransferase. Compounds 1 and 2 proved to be selective inhibitors of microbial enzymes.     

Synthesis and biological activity of N-methylated analogs of endomorphin-2

In this paper, we describe the synthesis of a series of endomorphin-2 analogs containing N-methylated amino acids, consecutively in each position. The μ-opioid receptor binding affinities of the new analogs were determined in the displacement experiments. Their in vivo antinociceptive activity was assessed in the hot-plate test in mice after central (icv) and peripheral (ip) administration. [Sar²]endomorphin-2, which had the highest μ-receptor affinity, also showed the strongest analgesic effect when administered centrally and was the only analog that retained activity after peripheral injection.     

Synthesis and biological evaluation of arylated novobiocin analogs as Hsp90 inhibitors

Novobiocin analogs lacking labile glycosidic ether have been designed, synthesized and evaluated for Hsp90 inhibitory activity. Replacement of the synthetically complex noviose sugar with simple aromatic side chains produced analogs that maintain moderate cytotoxic activity against MCF7 and SkBR3 breast cancer cell-lines. Rationale for the preparation of des-noviose novobiocin analogs in addition to their synthesis and biological evaluation are presented herein.     

Synthesis and biological activity of FGLamide allatostatin analogs with Phe3 residue modifications

A FGLamide allatostatin neuropeptide mimic ( H17 ) is a potential insect growth regulator which inhibits the production of juvenile hormone by the corpora allata. To find more evidence to reveal the structure–activity relationships of the Phe³ residue in the C‐terminal conserved pentapeptide and search for novel analogs with high activity, a series of Phe³ residue‐modified analogs were designed and synthesized using H17 as the lead compound. Bioassay using juvenile hormone (JH) production by corpora allata of the cockroach Diploptera punctata indicated that analogs 4 , 11 , and 13 showed strong ability to inhibit JH production in vitro, with IC₅₀ of 38.5, 22.5, and 26 nM, respectively. As well, the activity of analog 2 (IC₅₀: 89.5 nM) proved roughly equivalent to that of H17 . Based on the primary structure–activity relationships of Phe³ residue, we suggest that for analogs containing six‐membered aromatic rings, removing the methylene group of Phe³ or an o‐halogen or p‐halogen‐substituted benzene ring could increase the ability to inhibit biosynthesis of JH. This study will be useful for the design of new allatostatin analogs for insect management. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Isosteric analogs of lenalidomide and pomalidomide: Synthesis and biological activity

A series of analogs of the immunomodulary drugs lenalidomide (1) and pomalidomide (2), in which the amino group is replaced with various isosteres, was prepared and assayed for immunomodulatory activity and activity against cancer cell lines. The 4-methyl and 4-chloro analogs 4 and 15, respectively, displayed potent inhibition of tumor necrosis factor-α (TNF-α) in LPS-stimulated hPBMC, potent stimulation of IL-2 in a human T cell co-stimulation assay, and anti-proliferative activity against the Namalwa lymphoma cell line. Both of these analogs displayed oral bioavailability in rat.     

Synthesis and biological activity of five -Cys analogs of human insulin

Five analogs of human insulin with -Cys in different positions (A⁶, A⁷, A¹¹, A⁶⁺¹¹, B⁷) have been synthesized by the fragment condensation approach, combined with selective disulfide formation. All of them have physicochemical properties noticeably different from those of human insulin. They possess very low biological activity (0.03−1.2%, glucose oxidation in rat fat cells). In contrast, the potency for antibody binding ranges from 7 to 70% of that of insulin. The two analogs with -Cys in positions A⁶ and A⁷ have been obtained in crystalline form.     

Synthesis and biological activity of peptidyl aldehyde urokinase inhibitors

Solid- and solution-phase synthesis of peptidomimetic inhibitors of urokinase-type plasminogen activator based on the sequence dSerAlaArg-al are described. The biological activities of these unique inhibitors are reported herein. Carbonate prodrugs were prepared and tested as potential drug delivery systems.     

Synthesis and biological activity of selective azasugar-based TACE inhibitors

A series of azasugar-based hydroxamic acid derivatives bearing 2R,3R,4R,5R-configuration is described. Compound 4c with 4,5-O-acetonide group showed excellent in vitro potency against TACE, with high selectivity over MMP-1 and moderate selectivity over MMP-3 and MMP-9.     

Synthesis and biological activity of novel S-adenosyl-L-homocysteine hydrolase inhibitors

Four potential S-adenosyl-L-homocysteine hydrolase inhibitors were prepared and tested against purified recombinant rat liver enzyme. Preliminary studies indicate that three of these compounds, 1, 2, and 4, caused time-dependent inactivation of S-adenosyl-L-homocysteine hydrolase but showed a biphasic nature. Compound 3 was found to be a rapid equilibrium inhibitor of this enzyme.     

Synthesis, biological activity and conformational analysis of cyclic GRF analogs

A novel cyclic GRF analog, cyclo(Asp8-Lys12)-[Asp8,Ala15]-GRF(1-29)-NH2, i.e. cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2, was synthesized by the solid phase procedure and found to retain significant biological activity. Solid phase cyclization of Asp8 to Lys12 proceeded rapidly (approximately 2 h) using the BOP reagent. Substitution of Ala2 with D-Ala2 and/or NH2-terminal replacement (desNH2-Tyr1 or N-MeTyr1) in the cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 system resulted in highly potent analogs that were also active in vivo. Conformational analysis (circular dichroism and molecular dynamics calculations based on NOE-derived distance constraints) demonstrated that cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 contains a long alpha-helical segment even in aqueous solution. A series of cyclo8,12 stereoisomers containing D-Asp8 and/or D-Lys12 were prepared and also found to be highly potent and to retain significant alpha-helical conformation. The high biological activity of cyclo8,12[N-MeTyr1,D-Ala2,Asp8,Ala15]-GRF(1-29)- NH2 may be explained on the basis of retention of a preferred bioactive conformation.