Design, synthesis, and biological evaluation of HSP90 inhibitors based on conformational analysis of radicicol and its analogues

The molecular chaperone HSP90 is an attractive target for chemotherapy because its activity is required for the functional maturation of a number of oncogenes. Among the known inhibitors, radicicol, a 14-member macrolide, stands out as the most potent. A molecular dynamics/minimization of radicicol showed that there were three low energy conformers of the macrocycle. The lowest of these is the bioactive conformation observed in the cocrystal structure of radicicol with HSP90. Corresponding conformational analyses of several known analogues gave a good correlation between the bioactivity and the energy of the bioactive conformer, relative to other conformers. Based on this observation, a number of proposed analogues were analyzed for their propensity to adopt the bioactive conformation prior to synthesis. This led to the identification of pochonin D, a recently isolated secondary metabolite of Pochonia chlamydosporia, as a potential inhibitor of HSP90. Pochonin D was synthesized using polymer-bound reagents and shown to be nearly as potent an HSP90 inhibitor as radicicol.     

Synthetic ansamycins prepared by a ring-expanding Claisen rearrangement. Synthesis and biological evaluation of ring and conformational analogues of the Hsp90 molecular chaperone inhibitor geldanamycin

A series of ansa-quinones has been prepared by chemical synthesis, and evaluated by biological techniques. Thus, 19-membered ansa-lactams, simplified analogues of the naturally occurring Hsp90 molecular chaperone inhibitor geldanamycin, were obtained by concise routes, the key steps being the combination of a ring-closing metathesis to give a 17-membered ring followed by Claisen rearrangement to effect ring expansion. The methodology was also used to prepare an "unnatural" 18-membered ring analogue. In ATPase enzyme assays, the synthetic ansa-quinones were weak inhibitors of Hsp90.     

Inhibition of Hsp90 with Resorcylic Acid Macrolactones: Synthesis and Binding Studies

A series of resorcylic acid macrolactones, analogues of the natural product radicicol has been prepared by chemical synthesis, and evaluated as inhibitors of heat shock protein 90 (Hsp90), an emerging attractive target for novel cancer therapeutic agents. The synthesis involves acylation of an ortho‐toluic acid dianion, esterification, followed by a ring‐closing metathesis to form the macrocycle. Subsequent manipulation of the protected hydroxymethyl side chain allows access to a range of new analogues following deprotection of the two phenolic groups. Co‐crystallization of one of the new macrolactones with the N‐terminal domain of yeast Hsp90 confirms that it binds in a similar way to the natural product radicicol and to our previous synthetic analogues, but that the introduction of the additional hydroxymethyl substituent appears to result in an unexpected change in conformation of the macrocyclic ring. As a result of this conformational change, the compounds bound less favorably to Hsp90.     

一种新型Hsp90抑制剂的合成及其抑制活性

对氨基苯甲酸经重氮化后再与2-氯乙酰乙酸乙酯反应制得(Z)-4-[2-(1-氯-2-乙氧基-2-羰亚甲基)肼基]苯甲酸(1);1与二甲基环己二酮成环后再与对羟基环己胺完成酰胺化反应合成了一种新型Hsp90抑制剂——N-(4-羟基环己基)-4-[1-(6,6-二甲基-4-氧-3-乙酰氧基-4,5,6,7-四氢吲唑)]苯甲酰胺(3),其结构经1HNMR表征。荧光偏振法研究结果表明3对Hsp90α具有明显的抑制活性。     

Total synthesis and initial biological evaluation of new B-ring-modified bryostatin analogs

[Structure: see text] The total synthesis and preliminary biological evaluation of the first bryostatin analogs (bryologs) to incorporate B-ring substitution are reported. Asymmetric syntheses of two new polyketide "spacer" domains are described, one exploiting the pseudosymmetry of the C1-C13 region. These fragments are convergently joined to the "recognition" domain through a remarkably versatile macrotransacetalization process. The resulting new analogs exhibit potent nanomolar or picomolar affinity to protein kinase C (PKC), comparable to or better than that found for bryostatin.     

Deletion of the oxetane ring in docetaxel analogues: synthesis and biological evaluation

Two new docetaxel analogues have been prepared starting from 10-deacetylbaccatin III. Both derivatives lack the oxetane D-ring but possess the 4alpha-acetoxy group, which is important for biological activity. The influence of a more or less constrained C-ring was evaluated by adding, or not adding, a double bond in this ring. Both compounds were found to be equally less active than docetaxel in biological assays. [reaction: see text]     

Rational design,synthesis, and biological evaluation of novel C6-modified geldanamycin derivatives as potent Hsp90 inhibitors and anti-tumor agents

Heat shock protein 90 (Hsp90) is an appealing anticancer drug target that provoked a tremendous wave of investigations. Geldanamycin (GA) is the first identified Hsp90 inhibitor that exhibited potent anti-cancer activity, but the off-target toxicity associated with the benzoquinone moiety hampered its clinical application. Until now, structure optimization of GA is still in need to fully exploit the therapeutic value of Hsp90. Due to the structural complexity and synthetic challenge of this compound family, conventional optimization is bound to be costly but high efficiency is expected to be reachable by combining the art of rational design and total synthesis. Described in this paper is our first attempt at this approach aiming at rational modification of the C6-position of GA. The binding affinities towards Hsp90 of compound 1 (C6-ethyl) and 2 (C6-methyl) were designed and predicted by using Discovery Studio. These compounds were synthesized and further subjected to a thorough in vitro biological evaluation. We found that compounds 1 and 2 bind to Hsp90 protein with the IC₅₀ of 34.26 nmol/L and 163.7 nmol/L, respectively. Both compounds showed broad-spectrum antitumor effects. Replacing by ethyl, compound 1 exhibited more potent bioactivity than positive control GA, such as in G2/M cell cycle arrest, cell apoptosis and client proteins degradations. The results firstly indicated that the docking study is able to provide a precise prediction of Hsp90 affinities of GA analogues, and the C6 substituent of GA is not erasable without affecting its biological activity.     

Fluorinated peptidomimetics: synthesis, conformational and biological features

Peptides modified with fluoroalkyl functions in key backbone positions have been scarcely studied so far. Thus, little is known about their synthesis, their structural and physico-chemical properties, and their biological features. Our interest in this field of research led to the development of stereocontrolled synthetic protocols, both in solution and in solid phase, for many different fluoroalkyl peptidomimetics, some of which are overviewed in this paper: (a) ψ[CH(CF₃)NH]-peptide mimics holding a great potential as hybrids between natural peptides and hydrolytic transition state analogs; (b) trifluoromethyl (Tfm) malic peptidomimetics as micromolar inhibitors of some matrix metalloproteinases; (c) bis-Tfm analogs of Pepstatin A, that are nanomolar and selective inhibitors of the protozoal aspartyl protease Plasmepsin II.     

Novel triazolopeptides: chirospecific synthesis and conformational studies of proline derived analogs

Replacing the backbone amide function by a heterocyclic bioisostere, [3+2] azide-alkyne cycloaddition has been applied for the construction of biologically relevant peptidomimetics. Starting from aminoalkynoates, triazole formation was accomplished by addition of hydrazoic acid. NMR studies displayed that the newly developed 4,5-triazolopeptides, which incorporate a biomimetic triazole NH-function as polar constraint element, showed a substantially higher tendency to form a cis-prolyl-geometry than a comparable native peptide sequence.     

Total synthesis and biological evaluation of pederin, psymberin, and highly potent analogs

The potent cytotoxins pederin and psymberin have been prepared through concise synthetic routes (10 and 14 steps in the longest linear sequences, respectively) that proceed via a late-stage multicomponent approach to construct the N-acyl aminal linkages. This route allowed for the facile preparation of a number of analogs that were designed to explore the importance of the alkoxy group in the N-acyl aminal and functional groups in the two major subunits on biological activity. These analogs, including a pederin/psymberin chimera, were analyzed for their growth inhibitory effects, revealing several new potent cytotoxins and leading to postulates regarding the molecular conformational and hydrogen bonding patterns that are required for biological activity. Second generation analogs have been prepared based on the results of the initial assays and a structure-based model for the binding of these compounds to the ribosome. The growth inhibitory properties of these compounds are reported. These studies show the profound role that organic chemistry in general and specifically late-stage multicomponent reactions can play in the development of unique and potent effectors for biological responses.     

Design, synthesis, and evaluation of a radicicol and geldanamycin chimera, radamide

A chimera composed of the natural products radicicol and geldanamycin has been prepared through an amide linkage connecting the resorcinol moiety of radicicol to the quinone ring of geldanamycin. The inhibitory activity of these compounds was determined by their ability to inhibit Hsp90's inherent ATPase activity along with degradation of the Hsp90 client protein, HER-2 in MCF-7 breast cancer cells. [reaction: see text]     

Relationship among ligand conformations in solution, in the solid state, and at the Hsp90 binding site: geldanamycin and radicicol

The unknown effects of a receptor's environment on a ligand's conformation presents a difficult challenge in predicting feasible bioactive conformations, particularly if the receptor is ill-defined. The primary hypothesis of this work is that a structure's conformational ensemble in solution presents viable candidates for protein binding. The experimental solution profile can be achieved with the NAMFIS (NMR analysis of molecular flexibility in solution) method, which deconvolutes the average NMR spectrum of small flexible molecules into individual contributing conformations with varying populations. Geldanamycin and radicicol are structurally different macrocycles determined by X-ray crystallography to bind to a common site on the cellular chaperone heat shock protein 90 (Hsp90). Without benefit of a receptor structure, NAMFIS has identified the bioactive conformers of geldanamycin and radicicol in CDCl3 solution with populations of 4% and 21%, respectively. Conversely, docking the set of NAMFIS conformers into the unliganded proteins with GLIDE followed by MM-GBSA scoring reproduces the experimental crystallographic binding poses.     

Synthesis and biological evaluation of neopeltolide and analogs

The synthesis of neopeltolide analogues that contain variations in the oxazole-containing side chain and in the macrolide core are reported along with the GI(50) values for these compounds against MCF-7, HCT-116, and p53 knockout HCT-116 cell lines. Although biological activity is sensitive to changes in the macrocycle and the side chain, several analogues displayed GI(50) values of <25 nM. Neopeltolide and several of the more potent analogues were significantly less potent against p53 knockout cells, suggesting that p53 plays an auxiliary role in the activity of these compounds.     

The first oxalamide‐bridged ferrocene: Facile synthesis,preliminary conformational analysis and biological evaluation

tert ‐Butyl‐1′‐methoxycarbonyl‐1‐ferrocenecarbamate ( 1 ) was Boc‐deprotected to give free amine which underwent oxalyl chloride‐mediated dimerization. The structure of the so‐obtained oxalamide‐bridged ferrocene 2 was elucidated using infrared and NMR (¹H, ¹³C, COSY, NOESY, HSQC, HMBC) spectroscopies, crystal structure analysis, and electrospray ionization and high‐resolution mass spectrometry. The preliminary conformational analysis in solution suggested the intramolecular engagement of oxalamide protons, while single‐crystal analysis revealed an intermolecular hydrogen‐bonding pattern. Also, the effect of oxalamide‐bridged ferrocene 2 on cell viability of three human cell lines (HEK293T, HeLa and HepG2) was tested. In vitro screening revealed proliferative as well as cytotoxic effects of the tested compound in the applied concentration range (1–350 μM) on HEK293T and HepG2 cells. Stimulatory effect on cell growth was the most pronounced for normal HEK293T cells, while the highest cytotoxic effect was observed towards HeLa tumour cells and it was dose‐dependent. The observed dual biological activity of 2 implies its potential application in drug development.     

Design,synthesis, and insecticidal bioactivities evaluation of pyrrole- and dihydropyrrole-fused neonicotinoid analogs containing chlorothiazole ring

Chlorothiazole ring, as a substituted heterocycle, frequently occurred in structures of various insecticides, and brought positive effect on bioactivity. In purpose to find novel neonicotinoids, a series of pyrrole- and dihydropyrrole-fused neonicotinoid analogs containing chlorothiazole ring were synthesized for the first time. Results of the following biological assays showed that compounds 5a-c achieved good insecticidal activity against Aphis craccivora, and compound 5h exhibited good activity against Nilaparvata lugens.     

Synthesis and biological properties of novel structural analogs of isothiobarbamine

Russian Chemical Bulletin - Novel structural analogs of isothiobarbamine, which differ from the prototype scaffold by the substituent at position 2 of the pyrimidine heterocycle, were for the first...     

Substituted pyrazinecarboxamides: synthesis and biological evaluation

Condensation of the corresponding chlorides of some substituted pyrazine-2-carboxylic acids (pyrazine-2-carboxylic acid, 6-chloropyrazine-2-carboxylic acid, 5-tert-butylpyrazine-2-carboxylic acid or 5-tert-butyl-6-chloropyrazine-2-carboxylic acid) with various ring-substituted aminothiazoles or anilines yielded a series of amides. The syntheses, analytical and spectroscopic data of thirty newly prepared compounds are presented. Structure-activity relationships between the chemical structures and the anti-mycobacterial, antifungal and photosynthesis-inhibiting activity of the evaluated compounds are discussed. 3,5-Bromo-4-hydroxyphenyl derivatives of substituted pyrazinecarboxylic acid, 16-18, have shown the highest activity against Mycobacterium tuberculosis H(37)Rv (54-72% inhibition). The highest antifungal effect against Trichophyton mentagrophytes, the most susceptible fungal strain tested, was found for 5-tert-butyl-6-chloro-N-(4-methyl-1,3-thiazol-2-yl)pyrazine-2-carboxamide (8, MIC =31.25 micromol x mL(-1)). The most active inhibitors of oxygen evolution rate in spinach Molecules 2006, 11,243 chloroplasts were the compounds 5-tert-butyl-6-chloro-N-(5-bromo-2-hydroxyphenyl)- pyrazine-2-carboxamide (27, IC(50) = 41.9 micromol x L(-1)) and 5-tert-butyl-6-chloro-N-(1,3- thiazol-2-yl)-pyrazine-2-carboxamide (4, IC50 = 49.5 micromol x L(-1)).     

6,6-Spiroimine analogs of (-)-gymnodimine A: synthesis and biological evaluation on nicotinic acetylcholine receptors

Simple models of the spiroimine core of (-)-gymnodimine A have been synthesized in racemic and optically active forms. The quaternary carbon of the racemic spiroimines was created by Michael addition of a β-ketoester to acrolein, whereas the asymmetric allylic alkylation of the same β-ketoester was used to access the spiroimines in an enantioselective fashion. Both racemic and enantio-enriched mixtures were tested for their biological activities on Xenopus oocytes either expressing (human α4β2) or having incorporated (Torpedoα1(2)βγδ) nicotinic acetylcholine receptors (nAChRs). These spiroimine analogs of (-)-gymnodimine A inhibited acetylcholine-evoked nicotinic currents, but were less active than the phycotoxin. Our results reveal that the 6,6-spiroimine moiety is important for the blockade of nAChRs and support the hypothesis that it is one of the pharmacophores of this group of toxins.     

Convergent synthesis and discovery of a natural product-inspired paralog-selective Hsp90 inhibitor

A convergent synthesis of benzoquinone ansamycin analogs is described that proceeds by a sequence of metallacycle-mediated alkyne-alkyne coupling, followed by site- and stereoselective dihydroxylation and global carbamate formation. These studies have led to (1) validation of alkyne-alkyne coupling to produce geldanamycin analogs that lack the problematic quinone, (2) the discovery that C6-C7 bis-carbamate functionality is compatible with Hsp90 inhibition, and (3) the identification of 1 as a nonquinone geldanamycin-inspired paralog-selective Hsp90 inhibitor.