Constructing novel dihydrofuran and dihydroisoxazole analogues of isocombretastatin-4 as tubulin polymerization inhibitors through [3+2] reactions

Tubulin Inhibitors Binding to Colchicine-Site: A Review from 2015 to 2019

Due to the three domains of the colchicine-site which is conducive to the combination with small molecule compounds, colchicine-site on the tubulin has become a common target for antitumor drug development, and accordingly, a large number of tubulin inhibitors binding to the colchicine-site have been reported and evaluated over the past years. In this study, tubulin inhibitors targeting the colchicine-site and their application as antitumor agents were reviewed based on the literature from 2015 to 2019. Tubulin inhibitors were classified into ten categories according to the structural features, including colchicine derivatives, CA-4 analogs, chalcone analogs, coumarin analogs, indole hybrids, quinoline and quinazoline analogs, lignan and podophyllotoxin derivatives, phenothiazine analogs, N-heterocycle hybrids and others. Most of them displayed potent antitumor activity, including antiproliferative effects against Multi-Drug-Resistant (MDR) cell lines and antivascular properties, both in vitro and in vivo. In this review, the design, synthesis and the analysis of the structure-activity relationship of tubulin inhibitors targeting the colchicine-site were described in detail. In addition, multi-target inhibitors, anti-MDR compounds, and inhibitors bearing antitumor activity in vivo are further listed in tables to present a clear picture of potent tubulin inhibitors, which could be beneficial for medicinal chemistry researchers.

Exploring Diverse-Ring Analogues on Combretastatin A4 (CA-4) Olefin as Microtubule-Targeting Agents

Combretastatin-4 (CA-4) as a tubulin polymerization inhibitor draws extensive attentions. However, due to its weak stability of cis-olefin and poor metabolic stability, structure modifications on cis-configuration are being performed. In this work, we constructed a series of novel CA-4 analogues with linkers on olefin containing diphenylethanone, cis-locked dihydrofuran, α-substituted diphenylethanone, cyclobutane and cyclohexane on its cis-olefin. Cytotoxic activity of all analogues was measured by an SRB assay. Among them, compound 6b, a by-product in the preparation of diphenylethanone analogues, was found to be the most potent cytotoxic agents against HepG2 cells with IC₅₀ values of less than 0.5 μM. The two isomers of 6b induced cellular apoptosis tested by Annexin V-FITC and propidium iodide (PI) double staining, arrested cells in the G2/M phase by PI staining analysis, and disrupted microtubule network by immunohistochemistry study in HepG2 cells. Moreover, 6b-(E) displayed a dose-dependent inhibition effect for tubulin assembly in in vitro tubulin polymerization assay. In addition, molecular docking studies showed that two isomers of 6b could bind efficiently at colchicine binding site of tubulin similar to CA-4.

Chemoselective syntheses of spirodihydrofuryl and spirocyclopropyl barbiturates via cascade reactions of barbiturate-based olefins and acetylacetone

The Michael addition initiated ring closure reaction of barbiturate-based olefins and acetylacetone with NBS has been explored. The efficient and chemoselective approach for the synthesis of barbiturate-fused spirocycles was established. Spirodihydrofuryl barbiturates and spirocyclopropyl barbiturates were synthesized selectively via cascade reactions under different basic conditions in moderate to excellent yields. The structure of 2-(4-chlorophenyl)-1,1-diacetyl-5,7-dimethyl-5,7-diazaspiro[2,5]octane-4,6,8-trione was confirmed by single crystal X-ray diffraction analysis.

Chemodivergent and Stereoselective Access to Fused Isoxazoline Azetidines and Thietanes through [3 + 2]-Cycloadditions

By combining efficient methodologies for the preparation of substituted azetines and thietes with a highly regio- and diastereoselective [3 + 2]-cycloaddition, a straightforward pathway for the synthesis of fused isoxazoline azetidines and thietanes has been designed. With minimal steps and starting from commercial sources, a new library of elaborated architectures was synthesized opening up a new class of molecules with large potential in pharmacology. Finally, a retro [2 + 2]-cycloaddition leading to substituted isoxazoles is described.

Regiospecific formation of the nitromethyl-substituted 3-phenyl-4,5-dihydroisoxazole via [3 + 2] cycloaddition

ABSTRACT

5-(Nitromethyl)-3-phenyl-4,5-dihydroisoxazole was obtained as a product of a high-yielding [3 + 2] cycloaddition reaction of in situ-generated benzonitrile N-oxide and 3-nitroprop-1-ene. For the first time, the regiochemistry of this reaction was unambiguously proven by X-ray structural analysis. The quantum-chemical calculation performed at the M06-2X/6-31G(d) (PCM) theoretical level affords a basis for explaining the course of reaction as well as the nature of transition states. Next, further DFT calculations together with spectral data shed light on structural aspects of the product.

GRAPHICAL ABSTRACT