Novel B-ring modified allocolchicinoids of the NCME series: design, synthesis, antimicrotubule activity and cytotoxicity

Design, synthesis, and biological evaluation of biotinylated colchicine derivatives as potential antitumor agents

Chemical drug design based on the biochemical characteristics of cancer cells has become an important strategy for discovering new anti-tumour drugs to improve tumour targeting effects and reduce off-target toxicities. Colchicine is one of the most prominent and historically microtubule-targeting drugs, but its clinical applications are hindered by notorious adverse effects. In this study, we presented a novel tumour-specific conjugate 9 that consists of deacetylcolchicine (Deac), biotin, and a cleavable disulphide linker. 9 was found to exhibit potent anti-tumour activity and exerted higher selectivity between tumour and nontarget cells than Deac. The targeting moiety biotin might enhance the transport capability and selectivity of 9 to tumour cells via biotin receptor-mediated endocytosis. The tubulin polymerisation activity of 9 (with DTT) was close to the parent drug Deac. These preliminary results suggested that 9 is a high potency and reduced toxicity antitumor agent and worthy of further investigation.

Diastereoselective Access to Tetracyclic Eight-Membered Lactams through a Dearomative Heck Reaction and an Alkylative Ring-Opening Driven by Photoexcited Spiroindolines

An external-photocatalyst-free, light-driven alkylative ring-opening of stable spiroindolines was developed to construct indolo- and benzoannulated eight-membered lactams. The spiroindolines were prepared from tetrahydro-β-carbolines by a dearomative Heck reaction. Mechanistic experimental studies on the alkylative ring opening suggested that a photoredox pathway was involved, in which the spiroindoline performed as both reagent and photosensitizer. DFT calculations showed that the radical addition toward a cyclic alkene was the key to the diastereoselective formation of tetracyclic medium-sized lactams.

Pyrinap ligands for enantioselective syntheses of amines

Amines are a class of compounds of essential importance in organic synthesis, pharmaceuticals and agrochemicals. Due to the importance of chirality in many practical applications of amines, enantioselective syntheses of amines are of high current interest. Here, we wish to report the development of (R,R_a)-N-Nap-Pyrinap and (R,S_a)-N-Nap-Pyrinap ligands working with CuBr to catalyze the enantioselective A³-coupling of terminal alkynes, aldehydes, and amines affording optically active propargylic amines, which are platform molecules for the effective derivatization to different chiral amines. With a catalyst loading as low as 0.1 mol% even in gram scale reactions, this protocol is applied to the late stage modification of some drug molecules with highly sensitive functionalities and the asymmetric synthesis of the tubulin polymerization inhibitor (S)-(-)-N-acetylcolchinol in four steps. Mechanistic studies reveal that, unlike reported catalysts, a monomeric copper(I) complex bearing a single chiral ligand is involved in the enantioselectivity-determining step.

Colchicine Alkaloids and Synthetic Analogues: Current Progress and Perspectives

Colchicine, the main alkaloid of Colchicum autumnale, is one of the most famous natural molecules. Although colchicine belongs to the oldest drugs (in use since 1500 BC), its pharmacological potential as a lead structure is not yet fully exploited. This review is devoted to the synthesis and structure-activity relationships (SAR) of colchicine alkaloids and their analogues with modified A, B, and C rings, as well as hybrid compounds derived from colchicinoids including prodrugs, conjugates, and delivery systems. The systematization of a vast amount of information presented to date will create a paradigm for future studies of colchicinoids for neoplastic and various other diseases.

Tetrazole hybrids with potential anticancer activity

Cancer is one of the main causes of death throughout the world. The anticancer agents are indispensable for the treatment of various cancers, but most of them currently on the market are not specific, resulting in series of side effects of chemotherapy. Moreover, the emergency of drug-resistance towards cancers has already increased up to alarming level in the recent decades. Therefore, it's imperative to develop novel anticancer candidates with excellent activity against both drug-susceptible and drug-resistant cancers, and low toxicity as well. Tetrazole is the bioisoster of carboxylic acid, and its derivatives demonstrated promising anticancer activity. Hybridization of tetrazole with other anticancer pharmacophores may provide novel candidates with anticancer potency. The present review described the anticancer activity of tetrazole hybrids, and the structure-activity relationship (SAR) is also discussed to provide an insight for rational designs of tetrazole anticancer candidates with higher efficiency.

Ring-size-selective construction of fluorine-containing carbocycles via intramolecular iodoarylation of 1,1-difluoro-1-alkenes

1,1-Difluoro-1-alkenes bearing a biaryl-2-yl group effectively underwent site-selective intramolecular iodoarylation by the appropriate cationic iodine species. Iodoarylation of 2-(2-aryl-3,3-difluoroallyl)biaryls proceeded via regioselective carbon–carbon bond formation at the carbon atoms in β-position to the fluorine substituents, thereby constructing dibenzo-fused six-membered carbocycles bearing a difluoroiodomethyl group. In contrast, 2-(3,3-difluoroallyl)biaryls underwent a similar cyclization at the α-carbon atoms to afford ring-difluorinated seven-membered carbocycles.

Domino C-F Bond Activation of the CF3 Group: Synthesis of Fluorinated Dibenzo[a,c][7]annulenes from 2-(Trifluoromethyl)-1-alkenes and 2,2'-Diceriobiaryls

The construction of ring-fluorinated seven-membered carbocycles was readily achieved via the domino S_N2'-type/S_NV reaction between 2-(trifluoromethyl)-1-alkenes and 1,4-carbodianions. The S_N2'-type reaction of 2-(trifluoromethyl)-1-alkenes with 2,2'-diceriobiaryls generated the intermediary 1,1-difluoro-1-alkenes bearing a monoceriobiaryl moiety, which in turn underwent intramolecular S_NV reaction to afford fluorinated 5H-dibenzo[a,c][7]annulenes.

Chemical synthesis, pharmacological evaluation and in silico analysis of new 2,3,3a,4,5,6-hexahydrocyclopenta[c]pyrazole derivatives as potential anti-mitotic agents

We have synthesized new, biologically active mono- and di-substituted 2,3,3a,4,5,6-hexahydrocyclopenta[c]pyrazole derivatives bearing electron withdrawing groups and electron donating groups. These derivative structures were characterized by their spectral and analytical data. The newly synthesized hexahydropyrazole analogues were evaluated for their in vitro anticancer activity against breast and lung cancer cell lines using a cytotoxicity bioassay. To understand their mechanism of action, tubulin binding assays were performed which pointed to their binding to microtubules in a mode similar to but not identical to colchicine, as evidenced by their KD value evaluation. Computational docking studies also suggested binding near the colchicine binding site on tubulin. These results were further confirmed by colchicine-binding assays on the most active compounds, which indicated that they bound to tubulin near but not at the colchicine site. The moderate cytotoxic effects of these compounds may be due to the presence of electron donating groups on the para-position of the phenyl ring, along with the hexahydropyrazole core nucleus. The observed anti-cancer activity based on inhibition of microtubule formation may be helpful in designing more potent compounds with a hexahydropyrazole moiety.

Acetal-initiated Prins bicyclization for the synthesis of hexahydrofuro-[3,4-c]furan lignans and octahydropyrano[3,4-c]pyran derivatives

An acetal-initiated Prins bicyclization approach has been developed for the stereoselective synthesis of hexahydrofuro[3,4-c]furan lignans. This also provides a direct way to generate a new series of octahydropyrano[3,4-c]pyran derivatives in a single-step process.

Synthesis and biological evaluation of novel pyrazole derivatives with anticancer activity

We synthesized thirty-six novel pyrazole derivatives and studied their antiproliferative activity in human ovarian adenocarcinoma A2780 cells, human lung carcinoma A549 cells, and murine P388 leukemia cells. Four of these substances were selected because of their higher antiproliferative activity and further analyses showed that they were all able to induce apoptosis, although to a different extent. The expression of p53 and p21(waf1), which induce apoptosis and cell cycle arrest, was evaluated by western blot analysis in cells treated with compound 12d. The analysis of the cell cycle showed that all the selected compounds cause a partial G2/M block and the formation of polyploid cells. Furthermore, the four selected compounds were tested for their interaction with the microtubular cytoskeletal system by docking analysis, tubulin polymerization assay and immunofluorescence staining, demonstrating that the compound 12d, unlike the other active derivatives, was able to significantly bind dimers of α- and β-tubulin, probably causing a molecular distortion resulting in the disassembly of microtubules.

Intramolecular Nicholas reactions in the synthesis of dibenzocycloheptanes. Synthesis of allocolchicine NSC 51046 and analogues and the formal synthesis of (-)-allocolchicine

The preparation of dibenzocycloheptyne-Co(2)(CO)(6) complexes by intramolecular Nicholas reactions of biaryl-2-propargyl alcohol-Co(2)(CO)(6) derivatives is described. Reductive decomplexation of the dibenzocycloheptyne-Co(2)(CO)(6) complexes affords the corresponding dibenzocycloheptenes, individual members of which have been employed in a formal total synthesis of (-)-allocolchicine, the preparation of 6,7-dihydro-3,4,9,10,11-pentamethoxy-5H-dibenzo[a,c]cyclohepten-5-one, and the enantioselective total syntheses of NSC 51046 and its 3,8,9,10-tetramethoxy regioisomer.

Synthesis and tubulin-binding properties of new allocolchicinoids

Allocolchicinoids with B- and C-ring variations were synthesized using sequential enyne-metathesis/ Diels-Alder reactions (A-->AB-->ABC approach) and evaluated for their inhibitory effect on tubulin assembly in vitro. (-)-Allocolchicine 11 with methyl ester at C10 and (+/-)-cyclopropyl allocolchicinoid 32 exhibit similar activity than (-)-colchicine (1), probably derived from a similar flexibility in the biphenyl system. The presence of methyl ester at C10 led to a little loss in potency in comparison with the series with methyl ester at C9. A complete loss of activity was observed for allocolchicine 9 with methyl ester at C11.

A facile synthesis of pyrrolo-(di)-benzazocinones via an intramolecular N-acyliminium ion cyclisation

A facile, moderate to high yielding synthesis of hexahydro-(di)-benzazocinones is described via an intramolecular N-acyliminium ion cyclisation. The iminium ion intermediates are formed from the readily available 4,4-diethoxybutyl amides with an excess of triflic acid. For electron-withdrawing substituents, better yields were obtained from the pre-formed 2-hydroxypyrrolidine amides. From NMR studies, at ambient temperatures the pyrrolo-benzazocin-3-ones exist as a slowly equilibrating mixture of two conformations.

Colchicinoids from Colchicum crocifolium Boiss.: a case study in dereplication strategies for (-)-colchicine and related analogues using LC-MS and LC-PDA techniques

As a part of a project designed to investigate Colchicum species in Jordan, the chemical constituents of Colchicum crocifolium Boiss. (Colchicaceae) were investigated using LC-MS and LC-UV/Vis PDA. A decision tree for working with colchicinods has been developed by incorporating data from LC-UV/PDA and LC-MS. This dereplication strategy draws upon the UV/PDA spectra to classify compounds into one of four structural groups and combines this with retention time and mass spectra/molecular weight to identify the compounds. This strategy was applied on a small amount of extract (2 mg) of Colchicum crocifolium to dereplicate 10 known compounds from four different structural groups, namely (-)-demecolcine, 2-demethyl-(-)-colchicine or 3-demethyl-(-)-colchicine, N-deacetyl-(-)-colchicine, (-)-colchiciline, (-)-colchicine, beta-lumidemecolcine, 2-demethyl-beta-lumicolchicine or 3-demethyl-beta-lumicolchicine, N,N-dimethyl-N-deacetyl-beta-lumicornigerine, (-)-isoandrocymbine and (-)-autumnaline. Furthermore, a new compound was identi?ed as N,N-dimethyl-N-deacetyl-(-)-cornigerine. Three compounds, which had molecular ions at m/z 325, 340 and 374, could not be dereplicated into any obvious structural classes that have been isolated in our laboratories previously or reported in the literature.

Asymmetric Synthesis of Antimicrotubule Biaryl Hybrids of Allocolchicine and Steganacin

The asymmetric synthesis of novel axially chiral biaryl compounds 5 a-f containing a seven- or eight-membered heterocyclic medium ring is described. These molecules can be considered to be structural hybrids of allocolchicine- and steganacin-type natural products. The synthesis featured an atropo-diastereoselective biaryl Suzuki coupling in which a benzylic stereocenter efficiently transferred its stereochemical information to the biaryl axis. The coupling conditions were optimized, and two biphenylphosphane ligands (DavePhos and S-Phos) were found to give the highest yields and diastereoselectivities. A three-element stereochemical model was proposed to explain the observed diastereoselectivities. In a second key step, the medium ring of the target molecules was formed by a stereoselective S(N)1-type cyclodehydration that probably involved a configurationally stable carbocationic intermediate, as supported by calculations. Alternatively, S(N)2-type cyclizations were employed on the same Suzuki coupling products to give the target molecules in a stereodivergent or stereoconvergent manner. These cyclization methods furnished the target hybrid analogues 5 a-f with ee values above 94 %. All analogues were evaluated as antimicrotubule agents and against a panel of cancer-cell lines using colchicine (1) and N-acetylcolchinol (3) as references. Promising activities were found for R,aR-configured compounds 5 a, b and 5 f; in particular, ethyl analogue 5 b showed a twofold antimicrotubule activity relative to colchicine.

Three Distinct Reactions of 3,4-Dihydroisoquinolines with Azlactones: Novel Synthesis of Imidazoloisoquinolin-3-ones, Benzo[a]quinolizin-4-ones, and Benzo[d]azocin-4-ones

A facile and direct synthetic entry to tricyclic imidazoloisoquinolin-3-ones and benzo[a]quinolizin-4-ones is reported based on the ring annulation of 1-unsubstituted and 1-substituted dihydroisoquinolines with azlactones under neutral conditions in a one-step procedure. Bicyclic 2,3-dihydrobenzo[d]azocin-4-ones were also prepared using simple azlactone and 1-substituted dihydroisoquinolines in a one-pot reaction. [reaction: see text]

Application of Aryl Siloxane Cross-Coupling to the Synthesis of Allocolchicinoids

In this communication, we report a new approach to the allocolchicine carbocyclic skeleton based upon an aryl siloxane coupling reaction and a phenanthrol ring expansion. These key steps allow for the selective functionalization of every carbon within the carbocyclic framework. The siloxane coupling-phenanthrol sequence was applied to the synthesis of two allocolchicinoids, including the first fully synthetic approach to N-acetyl colchinol-O-methyl ether (NCME).

Asymmetric synthesis of propargylamides via 3,3'-disubstituted binaphthol-modified alkynylboronates

[reaction: see text] Alkynylboronates derived from 3,3'-disubstituted-2,2'-binaphthols react with various N-acylimines to give the expected chiral propargylamides with up to 99% ee. This new methodology was applied to the first enantioselective synthesis of the antitubulin agent (-)-N-acetylcolchinol.

Synthesis of (S)-(−)-N-acetylcolchinol using intramolecular biaryl oxidative coupling

An asymmetric synthesis of the tubulin polymerisation inhibitor (S)-(-)-N-acetylcolchinol is reported based on an intramolecular biaryl oxidative coupling of a 1,3-diarylpropyl acetamide intermediate using phenyliodonium bis(trifluoroacetate) as the final step. Three syntheses of the penultimate 1,3-diarylpropyl acetamide intermediate (S)-(-)-N-[1-[3-(tert-butyldimethylsilyloxy)phenyl)]-3-(3,4,5-trimethoxyphenyl)propyl] acetamide are described which differ in the means by which the stereogenic centre was introduced.

Two novel series of allocolchicinoids with modified seven membered B-rings: design, synthesis, inhibition of tubulin assembly and cytotoxicity

Two new attractive series of allocolchicinoids were designed as inhibitors of tubulin assembly using the potent ketone 4 and the tetracyclic, pyrazole annulated NCME variant 7 (NCME = N-acetyl colchinol-O-methylether (2)) as lead structures. The first group of inhibitors of type 6 with novel oxepine and azepine B-ring structures belongs to the NCME-series and was synthesized via a multistep total synthesis starting from simple and cheap 3-methoxybenzaldehyde (12) and 3,4,5-trimethoxybenzaldehyde (13). Biaryl-coupling of the starting materials 12 and 13 was accomplished via Ziegler-Ullmann-reaction to furnish the biphenyl 11 equipped with two carbaldehyde functions. The subsequent Cannizzaro reaction of this dicarbaldehyde 11 proceeded with high regioselectivity to yield almost exclusively the key compound, the hydroxymethyl carboxylic acid 9. Ring closure to the o,o'-bridged biphenyls was accomplished by two routes: on the one hand, treatment of 9 with aqueous hydrochloric acid yielded the lactone 15. On the other hand, a four step sequence starting from the isomeric mixture 9/10 furnished the constitutionally isomeric lactams 23 and 24; these could be converted to the corresponding thiolactams 25 and 26 and to the tetrazole annulated NCME-type derivatives 27 and 28. The second series of bioactive compounds are congeners of allocolchicine (3). The well known desacetyl allocolchicine (29) was easily oxidized to the oxime 30, which was further transformed to the corresponding ketone 31. This served as key precursor for the syntheses of various tetracyclic allocolchicine modifications 33-36 annulated with a pyrazole, isoxazole, pyrimidine or 2-aminopyrimidine heterocycle, respectively. Unexpectedly, all the NCME-variants with a substituent in position 7 like in NCME (2) inhibited the tubulin assembly only moderately. In contrast, the new series of allocolchicine modifications proved to be highly potent antimicrotubule agents. Inhibition of tubulin assembly occurred at lower concentrations compared to those measured for the reference colchicine (1). Surprisingly, these promising results could not be confirmed in the cytotoxicity tests against the human MCF-7 breast cancer cell line, where an unexpected loss of effectiveness compared to the corresponding NCME-derivatives was observed.

Allocolchicinoid Synthesis via Direct Arylation

[reaction: see text] A formal enantioselective synthesis of allocolchicine and a synthesis of a C-ring analogue have been achieved by employing an intramolecular direct arylation of an aryl chloride to form the biaryl carbon-carbon bond and the seven-membered ring.