Synthesis and antitumour activity of glycyrrhetinic acid derivatives

Glycyrrhetinic acid (GA) is one of many interesting triterpenoic acids showing anticancerogenic potential. GA is known to trigger apoptosis in tumour cell lines, although GA has a low cytotoxicity. In our study we were able to prepare derivatives of GA that show lowered the IC(50) values as determined by a sulforhodamine B (SRB) assay using 15 different human tumour cell lines. Thus, combining an ester group combined with the presence of an amino acid moiety led to a ca. 60-fold improved antitumor activity. Experiments on mouse embryonic fibroblasts (NiH3T3) revealed that these compounds showed a better selectivity for tumour cells compared to the parent compound GA. An apoptotic effect of some of these compounds was determined using an acridine orange/ethidium bromide (AO/EB) test and DNA laddering experiments.     

Synthesis and antitumour activity of sulfoalkyl derivatives of curdlan and lichenan.

2-Sulfoethyl, 3-sulfopropyl, and 4-sulfobutyl derivatives of the (1----3)-beta-D-glucan curdlan and the (1----3/1----4)-beta-D-glucan lichenan have been synthesised. The substituents are located mainly at positions 6. The curdlan derivatives strongly inhibited the growth of the Sarcoma 180 tumour, whereas the lichenan derivatives were inactive, indicating that a (1----3)-linked beta-D-glucan backbone is essential for activity.     

Antitumour benzothiazoles. Part 10: the synthesis and antitumour activity of benzothiazole substituted quinol derivatives

The synthesis of a series of new antitumour agents, the benzothiazole substituted quinol ethers and esters, is reported via the hypervalent iodine mediated oxidation of hydroxylated 2-phenylbenzothiazoles. The products were found to be active in vitro against human colon and breast cancer cell lines with IC50 values in the nanomolar range.     

Urea and carbamate derivatives of primaquine: Synthesis,cytostatic and antioxidant activities

The novel urea primaquine derivatives 3 were prepared by aminolysis of primaquine benzotriazolide 2 with several hydroxyamines and ethylendiamine, while carbamates 4 were synthesized from the same precursor 2 and alcohols. All compounds are fully chemically characterized and evaluated for their cytostatic and antioxidant activities. The most prominent antiproliferative activity was obtained by compounds 3c, 3d, 3g, and 5b (IC₅₀ = 9–40 μM). 1-(5-Hydroxypentyl)-3-[4-(6-methoxy-quinolin-8-ylamino)-pentyl]urea (3c) showed extreme selectivity toward SW 620 colon cancer cells (IC₅₀ = 0.2 μM) and a bit less toward lung cancer cells H 460. Hydroxyurea 3h showed the highest interaction with DPPH. Primaquine twin drug 3g showed very significant inhibition on LOX soybean (IC₅₀ = 62 μM). Almost all the tested derivatives highly inhibited lipid peroxidation, significantly stronger than primaquine phosphate.     

Synthesis and antitumour activity of derivatives of curdlan and lichenan branched at C-6.

Derivatives of curdlan and lichenan, linear (1----3)-beta-D- and (1----3/1----4)-beta-D-glucans, respectively, have been synthesised having alpha-L-arabinofuranosyl, alpha-L-rhamnosyl, beta-D-glucosyl, and beta-gentiobiosyl side chains attached at positions 6. These water-soluble derivatives, obtained by condensation of the 2,4- and 2,4-/2,3-di-O-phenylcarbamoyl derivatives of curdlan and lichenan, respectively, with appropriate ortho esters followed by saponification, were characterised by methylation analysis, g.p.c., and interaction with Congo Red. The curdlan derivatives and the lichenan derivative with few glucosyl branches were active against the Sarcoma 180.     

Synthesis and cytotoxicity of 17a-aza-D-homo-androster-17-one derivatives

A series of 17a-aza-d-homo-andrester-17-one derivatives, bearing hydroxyl, hydroximino, carbonyl and thiosemicarbazido groups at the position-3 or position-6 of steroidal nucleus, were prepared and evaluated in vitro against two human cell lines (Hela (human cervical carcinoma) and SMMC 7404 (human liver carcinoma)). The results showed that these compounds could exhibit a high cytotoxicity to Hela tumor cell line, especially for compounds 8 and 12, the IC₅₀ values are 15.1 and 14.0 nmol/mL, respectively. Our findings could provide new evidence showing the relationship between the chemical structure and biological activity and may be useful for the discovery of new anti-cancer drugs.     

Antitumor agents. Part 236: Synthesis of water-soluble colchicine derivatives

Water-soluble colchicine derivatives were synthesized from 2-demethylcolchicine and 2-demethylthiocolchicine and evaluated in vitro against human tumor cell replication and for inhibition of tubulin polymerization. The glycinate esters (4, 5) and their tartaric acid salts (4a, 5a) showed potent cytotoxic activity in three different tumor cell lines with IC(50) values ranging from 0.02 to 0.88 microg/mL. The thiocolchicine analogs (5, 5a) were more potent than the colchicine analogs (4, 4a) in the tubulin polymerization assay. In particular, the water-soluble salt 5a merits preclinical development as an antitumor agent.     

Bioreversible phosphate protective groups: Synthesis and stability of model acyloxymethyl phosphates

Six bis(acyloxymethyl) esters of phenyl phosphate and benzyl phosphate and three acyloxymethylbenzylphenyl phosphates were prepared. Debenzylation of benzyl analogs gave respective free acids which were isolated as cyclohexylammonium salts. Stability of bis(acyloxymethyl)phenyl phosphates were studied in various aqueous buffers, hog liver esterase, and mice plasma.     

Polycations. 17. Synthesis and properties of polycationic derivatives of carbohydrates

In our continuing investigation of polycationic salts for purposes of antimicrobial action, ion-channel blocking, and construction of ionic liquids, we have prepared several series of polycationic salts derived from carbohydrate precursors. These salts are currently being investigated for optimal efficacy as antibacterials and antifungals, as well as for other applications. The syntheses of such series of salts are described here along with preliminary antibacterial testing results and a discussion of their properties indicating their potential utility for several purposes.     

NO-donors. Part 17: Synthesis and antimicrobial activity of novel ketoconazole-NO-donor hybrid compounds

Novel hybrid compounds combining the antifungal drug ketoconazole with a diazen-1-ium-1,2-diolate or an organic nitrate moiety and the corresponding NO-donors without ketoconazole were synthesized and their activities against a broad variety of fungal strains were tested. Hybridization modifies the spectrum of antimicrobial activities and generally, the ketoconazole-NO-donor hybrids are more potent than ketoconazole. The NO-donors alone show insufficient effectiveness.     

Potential bile acid metabolites. 17. Synthesis of 2 beta-hydroxylated bile acids

The 2 beta-hydroxylated derivatives of lithocholic, chenodeoxycholic, deoxycholic, and cholic acids were synthesized from the respective parent bile acids by established procedures. The principal reactions involved were (1) bromination of 3-oxo formylated bile acids in N,N-dimethylformamide, (2) rearrangement and substitution of the resulting 4 beta-bromo-3-oxo derivatives to the 2 beta-acetoxy-3-oxo compounds with potassium acetate, and (3) reduction to the 2 beta-acetoxy-3 alpha-hydroxy compounds with tert-butylamine-borane complex. As for the prepared 2 beta-hydroxylated bile acids with a diequatorial trans-glycol structure, proton and carbon-13 nuclear magnetic resonance spectroscopic and gas-liquid chromatographic/mass spectrometric properties are discussed.     

NO donors. Part 18: Bioactive metabolites of GTN and PETN—Synthesis and vasorelaxant properties

The vasodilators glyceryl trinitrate (GTN) and pentaerythrityl tetranitrate (PETN) are supposed to be degraded in vivo to the lower nitrates PETriN, PEDN, PEMN, 1,2-GDN, 1,3-GDN, 1-GMN, and 2-GMN. We synthesized these bioactive metabolites as reference compounds for pharmacokinetic studies. The use of HPLC-methods for monitoring the stepwise reduction of PETN to lower nitrates and the syntheses of the glyceryl dinitrates proved advantageous. Furthermore, we measured the vasorelaxant properties of all metabolites by performing organ bath experiments with porcine pulmonary arteries. In general, the vasodilator potency increases with the number of nitrate moieties in the compound.     

Synthesis and biological activities of novel 17-aminogeldanamycin derivatives

Geldanamycin interferes with the action of heat shock protein 90 (Hsp90) by binding to the N-terminal ATP binding site and inhibiting an essential ATPase activity. In a program directed toward finding potent, water soluble inhibitors of Hsp90, we prepared a library of over sixty 17-alkylamino-17-demethoxygeldanamycin analogs, and compared their affinity for Hsp90, ability to inhibit growth of SKBr3 mammalian cells, and in selected cases, water solubility. Over 20 analogs showed cell growth inhibition potencies similar to that of 17-allylamino-17-demethoxygeldanamycin (17-AAG), the front-runner geldanamycin analog that is currently in multiple clinical trials. Many of these analogs showed water solubility properties that were desirable for formulation. One of the most potent and water-soluble analogs in the series was 17-(2-dimethylaminoethyl)amino-17-demethoxygeldanamycin (17-DMAG), which was independently prepared by the NCI and will soon enter clinical trials. Importantly, the binding affinity of these analogs to the molecular target Hsp90 does not correlate well with their cytotoxicity in SKBr3 cells.     

Synthesis and antimycobacterial activity of capuramycin analogues. Part 2: acylated derivatives of capuramycin-related compounds

Acylated derivatives of capuramycin and A-500359A were synthesized and tested for antimycobacterial activity. Compound 20 having a decanoyl group showed very potent activity.     

Synthesis of 6- and 7-hydroxyestradiol 17-sulfates: the potential metabolites of estradiol 17-sulfate by female rat liver microsomes.

The potential ring-B hydroxylated metabolites of estradiol 17-sulfate (1) by female rat liver microsomes were chemically prepared as authentic compounds. They are 6alpha- and 6beta-hydroxyestradiol 17-sulfates (7 and 9), and 7alpha- and 7beta-hydroxyestradiol 17-sulfates (12 and 16), whose synthetic procedures are described.     

Concepts for the syntheses of biotinylated steroids. Part II: 17beta-estradiol derivatives as immunochemical probes

Biotinylated 17beta-estradiol (E2) derivatives are helpful probes for a better understanding of biospecific E2 interactions with steroid-binding proteins such as the estrogen receptor and anti-steroid antibodies. We describe synthetic strategies for the biotinylation of E2 toward the 3, 6alpha, and 7alpha positions using biotinyl-N-hydroxysuccinimide esters with different spacers, varying in structure and chain length. Key reaction for biotinylation at the 3 position is the regioselective ether formation of the phenolate E2 anion with a linker mesylate without protecting the 17beta-hydroxyl group. The 6alpha position is accessible via a 3,17beta protected 6alpha-hydroxy E2, prepared by stereospecific sodium borohydride reduction of 6-oxo E2. Direct cyanoethylation of the alcohol followed by reduction to the amine allows the biotinylation to 6alpha-O-coupled cyanoethyloxy linker E2 derivatives. Alternatively, 6alpha-O-coupled cyanoalkyloxy polyether linker E2 probes are obtained by a Williamson ether synthesis of the alcohol precursor with omega-t-butyl-dimethylsilyloxy-5-oxa-nonylmesylate. Cyanoethylation of the desilylated compound and further reduction of the nitrile led to the terminal amine. Reductive amination of the 3, 17beta acetylated 6-oxo E2 compound with 6-cyanoethyloxyhexyl ammonium acetate yields in a mixture of 6alpha/beta-N-alkylated E2 nitriles. The epimers are separated by reversed-phase HPLC and the 6alpha-compound subsequently reduced to the terminal amine. The 7alpha-biotinylated E2 compound is derived from 7alpha-(11'-undecyl-N-methyl-N-butylamide) E2, which is already known from literature. Subsequently, the 3 and 17beta positions are protected, and the amide is reduced to the 7alpha-(11'-undecanol) compound. Further cyanoethylation and reduction led to the 11'-amino-ethyloxyundecyl E2. Using (1)H NMR analysis, it could be shown that the biotin moiety of the biotinylated 6alpha- and 7alpha-E2 derivatives has an axial position which results in a vertical orientation of the substituent toward the alpha-face of the planar tetracyclic backbone. Thus, a negligible alteration of the original structure of the upper beta-face offers the feasibility of applying the 6alpha- and 7alpha-derivatives as optimal tracers in competitive immunoassays.     

Synthesis of carbamate derivatives of iejimalides. Retention of normal antiproliferative activity and localization of binding in cancer cells

The syntheses of six iejimalide carbamate derivatives are described. Their biological activity and those of the unmodified iejimalides A and B against breast and prostate cancer cell lines were determined. These results show that the serine hydroxyl group of iejimalides A and B is a permissive site that can be functionalized to form carbamate derivatives without significant loss of normal biological activity. This method of derivatization will be valuable for cellular target identification, mechanism of action studies, and drug development efforts. A fluorescent derivative does not exhibit binding to the cytoskeletal features of cancer cells.     

Microbial models of animal drug metabolism: Part 5. Microbial preparation of human hydroxylated metabolites of irbesartan

An exhaustive screening of fungal and microbial strains allowed to select the best microorganisms to produce in high yields some of the animal metabolites of an antihypertensive drug, irbesartan, in order to elucidate their structural and stereochemical characteristics. Among the microorganisms tested, bacteria, and especially Streptomycesstrains, were the most active producers of the main metabolites which included diastereomeric derivatives hydroxylated in the spirocyclopentane ring, open rearranged hydroxylated derivatives, and a putative N-glycosidic conjugate of irbesartan.