Antineoplastic agents. 578. Synthesis of stilstatins 1 and 2 and their water-soluble prodrugs

Cobalt(III)-catalyzed weakly coordinating arylurea-directed regioselective mono-olefination

Here, we developed an air-stable, earth-abundant cobalt(III)-catalyzed regioselective mono-olefination of arenes directed by urea under mild conditions through a cross-dehydrogenative coupling (CDC) process. Under the optimized conditions, a high regioselectivity of mono-olefination was achieved with various electron-rich and electron-deficient arenes, which afforded E-alkenylated products (with yields of up to 90%). In contrast to the conditions used for noble-metal-catalyzed olefination directed by weakly coordinating groups, our reaction was operated under mild conditions, including mild temperature (40 °C) and non-metallic oxidant.

Cloning and Expression of a Perilla frutescens Cytochrome P450 Enzyme Catalyzing the Hydroxylation of Phenylpropenes

Phenylpropanoid volatile components in plants are useful and valuable not only as flavorings, but also as medicines and food supplements. The pharmacological actions and toxicities of these compounds have been well studied but their synthetic pathways are generally unclear. In this study, we mined expressed sequence tag libraries of pure strains of perilla maintained for over 30 years for their oil type and conducted gas chromatography-mass spectrometry analyses of the perilla oils to confirm the presence of monohydrates speculated to be intermediates of the phenylpropene synthetics pathways. These putative monohydrate intermediates and their regioisomers were synthesized to identify the reaction products of assays of heterologously expressed enzymes. An enzyme involved in the synthesis of a phenylpropanoid volatile component was identified in perilla. Expression of this enzyme in Saccharomyces cerevisiae showed that it is a member of the cytochrome P450 family and catalyzes the introduction of a hydroxy group onto myristicin to form an intermediate of dillapiole. The enzyme had high sequence similarity to a CYP71D family enzyme, high regiospecificity, and low substrate specificity. This study may aid the elucidation of generally unexploited biosynthetic pathways of phenylpropanoid volatile components.

Combretastatin-based compounds with therapeutic characteristics: a patent review

Introduction: Combretastatins represent a potent class of phenolic-stilbene natural products that function as colchicine binding site inhibitors of tubulin polymerization and have been advanced as promising anticancer lead compounds. Among them, combretastatin A-4 is the most potent lead molecule due to its broad spectrum cytotoxicity against a variety of tumors. However, low water solubility due to its high lipophilic nature and inter-conversion of olefinic double bond from more active cis to less active trans-conformation poses limitations to its clinical utility. However, different approaches including prodrugs, salt formations, structural modifications, prevention of inter-conversion of the olefinic bond and changes to the substitution pattern on the rings of combretastatin A-4 were investigated and successfully resulted in different combretastatin-based molecules that demonstrated varying levels of potency against different types of tumors during their in-vitro and in-vivo studies. Areas covered: This review covers the patents over a period of 2008-2018. Expert opinion: Molecular hybridization and prodrug designing imparted multi-targeted actions to combretastatin derivatives. Currently, various combretastatin derivatives are under clinical trials. These derivatives could be used to treat disorders other than cancer, due to their vascular disrupting action.

Synthesis of dihydronaphthalene analogues inspired by combretastatin A-4 and their biological evaluation as anticancer agents

The natural products colchicine and combretastatin A-4 (CA4) have provided inspiration for the discovery and development of a wide array of derivatives and analogues that inhibit tubulin polymerization through a binding interaction at the colchicine site on β-tubulin. A water-soluble phosphate prodrug salt of CA4 (referred to as CA4P) has demonstrated the ability to selectively damage tumor-associated vasculature and ushered in a new class of developmental anticancer agents known as vascular disrupting agents (VDAs). Through a long-term program of structure activity relationship (SAR) driven inquiry, we discovered that the dihydronaphthalene molecular scaffold provided access to small-molecule inhibitors of tubulin polymerization. In particular, a dihydronaphthalene analogue bearing a pendant trimethoxy aryl ring (referred to as KGP03) and a similar aroyl ring (referred to as KGP413) were potent inhibitors of tubulin polymerization (IC50 = 1.0 and 1.2 μM, respectively) and displayed low nM cytotoxicity against human cancer cell lines. In order to enhance water-solubility for in vivo evaluation, the corresponding phosphate prodrug salts (KGP04 and KGP152, respectively) were synthesized. In a preliminary in vivo study in a SCID-BALB/c mouse model bearing the human breast tumor MDA-MB-231-luc, a 99% reduction in signal was observed with bioluminescence imaging (BLI) 4 h after IP administration of KGP152 (200 mg kg-1) indicating reduced tumor blood flow. In a separate study, disruption of tumor-associated blood flow in a Fischer rat bearing an A549-luc human lung tumor was observed by color Doppler ultrasound following administration of KGP04 (15 mg kg-1).

Synthesis and Characterization of a Phosphate Prodrug of Isoliquiritigenin

Isoliquiritigenin (1) possesses a variety of biological activities in vitro. However, its poor aqueous solubility limits its use for subsequent in vivo experimentation. In order to enable the use of 1 for in vivo studies without the use of toxic carriers or cosolvents, a phosphate prodrug strategy was implemented relying on the availability of phenol groups in the molecule. In this study, a phosphate group was added to position C-4 of 1, leading to the more water-soluble prodrug 2 and its ammonium salt 3, which possesses increased stability compared to 2. Herein are reported the synthesis, characterization, solubility, and stability of phosphate prodrug 3 in biological medium in comparison to 1, as well as new results on its anti-inflammatory properties in vivo. As designed, the solubility of prodrug 3 was superior to that of the parent natural product 1 (9.6 mg/mL as opposed to 3.9 μg/mL). Prodrug 3 as an ammonium salt was also found to possess excellent stability as a solid and in aqueous solution, as opposed to its phosphoric acid precursor 2.

cis-Restricted 3-aminopyrazole analogues of combretastatins: synthesis from plant polyalkoxybenzenes and biological evaluation in the cytotoxicity and phenotypic sea urchin embryo assays

We have synthesized a series of novel cis-restricted 4,5-polyalkoxydiaryl-3-aminopyrazole analogues of combretastatins via short synthetic sequences using building blocks isolated from dill and parsley seed extracts. The resulting compounds were tested in vivo in the phenotypic sea urchin embryo assay to reveal their antimitotic and antitubulin effects. The most potent aminopyrazole, 14a, altered embryonic cell division at 10 nM concentration, exhibiting microtubule-destabilizing properties. Compounds 12a and 14a displayed pronounced cytotoxicity in the NCI60 anticancer drug screen, with the ability to inhibit growth of multi-drug-resistant cancer cells.

Synthesis and biochemical activities of antiproliferative amino acid and phosphate derivatives of microtubule-disrupting β-lactam combretastatins

The synthesis and biochemical activities of novel water-soluble β-lactam analogues of combretastatin A-4 are described. The first series of compounds investigated, β-lactam phosphate esters 7a, 8a and 9a, exhibited potent antiproliferative activity and caused microtubule disruption in human breast carcinoma-derived MCF-7 cells. They did not inhibit tubulin polymerisation in vitro, indicating that biotransformation was necessary for their antiproliferative and tubulin binding effects in MCF-7 cells. The second series of compounds, β-lactam amino acid amides (including 10k and 11l) displayed potent antiproliferative activity in MCF-7 cells, disrupted microtubules in MCF-7 cells and also inhibited the polymerisation of tubulin in vitro. This indicates that the β-lactam amides did not require metabolic activation to have antiproliferative effects, in contrast to the phosphate series. Both series of compounds caused mitotic catastrophe and apoptosis in MCF-7 cells. Molecular modelling studies indicated potential binding conformations for the β-lactam amino acid amides 10k and 11l in the colchicine-binding site of tubulin. Due to their aqueous solubility and potent biochemical effects, these compounds are promising candidates for further development as microtubule-disrupting agents.

Antineoplastic agents. 548. Synthesis of iodo- and diiodocombstatin phosphate prodrugs

Toward the objective of designing a structurally modified analogue of the combretastatin A-4 phosphate prodrug (1b) with the potential for increased specificity toward thyroid carcinoma, synthesis of a series of iodocombstatin phosphate (11a-h) and diiodocombstatin phosphate prodrugs (12a-h) has been accomplished. The diiodo series was obtained via 8a and 9c from condensation of 4 and 6, and the iodo sequence involved a parallel pathway. Both series of iodocombstatins were found to display significant to powerful inhibition of the growth of a panel of human cancer cell lines and of the murine P388 lymphocytic leukemia cell line. Of the diiodo series, 12a was also found to markedly inhibit growth of pediatric neuroblastoma, and monoiodocombstatin 9a strongly inhibited HUVEC growth. Overall, the strongest activity was found against the breast, CNS, leukemia, lung, and prostate cancer cell lines and the least activity against the pancreas and colon lines. Parallel biological investigations of tubulin interaction, antiangiogenesis, and antimicrobial effects were also conducted.

Antineoplastic agents. 579. Synthesis and cancer cell growth evaluation of E-stilstatin 3: a resveratrol structural modification

As an extension of our earlier structure/activity investigation of resveratrol (1a) cancer cell growth inhibitory activity compared to the structurally related stilbene combretastatin series (e.g., 2a), an efficient synthesis of E-stilstatin 3 (3a) and its phosphate prodrug 3b was completed. The trans-stilbene 3a was obtained using a convergent synthesis employing a Wittig reaction with phosphonium bromide 9 as the key reaction step. Deprotection of the Z-silyl ether 13 gave E-stilstatin 3 (3a) as the exclusive product. The structure and stereochemistry of 3a was confirmed by X-ray crystal structure determination.