HIV-Inhibitory prenylated xanthones and flavones from Maclura tinctoria.

The organic extract of the plant Maclura tinctoria exhibited moderate anti-HIV activity. Seven prenylated phenolic derivatives were isolated from the active fractions and characterized by spectroanalytical methods. New compounds macluraxanthone B (1), macluraxanthone C (2), and dihydrocudraflavone B (8) were identified.

Cycloviolins A-D, anti-HIV macrocyclic peptides from Leonia cymosa.

Four novel anti-HIV macrocyclic peptides containing 28-31 amino acid residues, named cycloviolins A-D, have been isolated from the hitherto unstudied tropical plant Leonia cymosa. Their primary structure, including amino acid composition and sequence, was determined by a combination of MALDI-TOF and FAB MS and by enzymatic digestion of reduced derivatives, followed by Edman degradation and mass analyses. All of the cycloviolins contain six cysteines, which are present as three intramolecular disulfide bridges. Intriguingly, cycloviolins A-D showed high degrees of sequence homology to the known cyclopsychotride A and circulins A and B from the Rubiaceae family but much less homology to the varv peptides from Viola, a member of the same family (Violaceae).

New circulin macrocyclic polypeptides from Chassalia parvifolia.

Four new macrocyclic polypeptides were isolated and identified from an extract of the tropical tree Chassalia parvifolia. Circulins C-F are 29-30 amino acid cyclic peptides in which the entire primary amino acid chain is covalently cyclized via peptide bonds. Their structures were deduced from a combination of FABMS analyses, N-terminal Edman degradation, endoproteinase digestion, and amino acid analyses. All the peptides share a high degree of sequence homology and contain six cysteine residues forming three intramolecular disulfide bridges. Circulins C-F inhibited the cytopathic effects of in vitro HIV-1 infection with EC(50) values of 50-275 nM.

Cytotoxic and tubulin-interactive hemiasterlins from Auletta sp. and Siphonochalina spp. sponges.

Chemical and biological investigations of extracts from the sponge genus Auletta and two collections of Siphonochalina sp. have shown these organisms to be producers of the potent hemiasterlin class of antitumor agents. In addition to the previously known hemiasterlin (1) and hemiasterlin A (2), a new analogue, hemiasterlin C (3), was isolated and identified. The structures of 1 and 2 were assigned based on comparison to literature values, and 3 was identified on the basis of 1H NMR, 13C NMR, COSY, HSQC, and HMBC experiments. The cytotoxic and antitubulin activities of 1-3 were evaluated. In a comparative assay for inhibition of tubulin polymerization, the hemiasterlins were more potent than dolastatin 15 and equipotent with cryptophycin 1, but were somewhat less potent than dolastatin 10.

Alertenone, a dimer of suberosenone from Alertigorgia sp.

Bioassay-guided fractionation of organic extracts of the gorgonian Alertigorgia sp. has yielded the previously known suberosenone (1), a cytotoxic tricyclic sesquiterpene of the quadrone class, and alertenone (2), a dimer of suberosenone. The structure of 2 was determined by spectral analysis; the 1D TOCSY experiment was particularly useful in the structure elucidation. Comparison of the in vitro cytotoxicity of alertenone and suberosenone revealed that the dimeric alertenone was devoid of cytotoxicity below 35 microg/mL. In a hollow-fiber assay model of in vivo activity, suberosenone exhibited some growth inhibition of two of six tumor cell lines tested.

Vismiaphenones D-G, new prenylated benzophenones from Vismia cayennensis.

Following anti-HIV bioassay-guided fractionation, four new prenylated benzophenones, vismiaphenones D-G (7-10), were isolated from extracts of leaves of Vismia cayennensis. The structures were elucidated by spectral analyses. Only vismiaphenone D (7) exhibited HIV-inhibitory activity in the NCI primary screen.

Structure-activity requirements for flavone cytotoxicity and binding to tubulin.

A series of 79 flavones related to centaureidin (3,6,4'-trimethoxy-5, 7,3'-trihydroxyflavone, 1) was screened for cytotoxicity in the NCI in vitro 60-cell line human tumor screen. The resulting cytotoxicity profiles of these flavones were compared for degree of similarity to the profile of 1. Selected compounds were further evaluated with in vitro assays of tubulin polymerization and [3H]colchicine binding to tubulin. Maximum potencies for tubulin interaction and production of differential cytotoxicity profiles characteristic of 1 were observed only with compounds containing hydroxyl substituents at C-3' and C-5 and methoxyl groups at C-3 and C-4'.

HIV-inhibitory and cytotoxic oligostilbenes from the leaves of Hopea malibato.

Three new oligostilbenes, malibatols A (1) and B (2) and dibalanocarpol (3), together with one known oligostilbene balanocarpol (4), were isolated from the organic extract of the leaves of Hopea malibato. The structure elucidation of these compounds was based on the interpretation of their chemical and spectral data. Compounds 3 and 4 exhibited very modest HIV-inhibitory activity, while compounds 1 and 2 were cytotoxic to the host cells (CEM SS) in the antiviral assay.

Isolation of a novel Kunitz family protease inhibitor in association with Tethya hemolysin from the sponge Tethya ingalli.

Aqueous extracts from the New Zealand sponge Tethya ingalli (Hadromerida) displayed potent cytotoxicity in the NCI's 60-cell-line human tumor panel. Fractionation of the extract by ammonium sulfate precipitation, gel filtration, ultrafiltration, and both hydrophobic interaction and reversed-phase chromatography resulted in the isolation of two biologically active proteins. The first protein, Tethya protease inhibitor (TPI), which was purified to homogeneity, inhibited trypsin with an EC50 of 65 nM. TPI had a molecular mass of 11,431 Da, and an isoelectric point of 8.2. A partial N-terminal amino acid sequence determined for TPI showed significant homology with protease inhibitors of the Kunitz family. The second isolated protein displayed potent cytotoxicity, with pronounced selectivity for certain tumor cell lines (e.g., ovarian, renal, CNS, and breast). The latter protein, which had an apparent molecular weight of 21 kDa (SDS-PAGE), also lysed human red blood cells (EC50 of 39 nM) and was similar to a hemolysin previously isolated from the sponge Tethya lycinurium.

Isolation, primary sequence determination, and disulfide bond structure of cyanovirin-N, an anti-HIV (human immunodeficiency virus) protein from the cyanobacterium Nostoc ellipsosporum.

A novel anti-HIV protein, cyanovirin-N (CV-N), was isolated from an aqueous cellular extract of the cultured cyanobacterium (blue-green alga) Nostoc ellipsosporum, purified by reverse-phase HPLC, and sequenced by N-terminal Edman degradation of the intact protein and peptide fragments produced by endoproteinase digestions. CV-N consists of a single 101 amino acid chain which exhibits significant internal sequence duplication, but no significant homology to previously described proteins or to the transcription products of known nucleotide sequences. Alignment of residues 1-50 with residues 51-101 reveals 13 conservative amino acid changes as well as direct homology between 16 amino acid residues. CV-N contains four cysteines which form two intrachain disulfide bonds. The positions of the disulfide linkages were established by fast atom bombardment mass spectral studies of peptide fragments generated by a tryptic digestion of the native protein. Reductive cleavage of these crosslinks resulted in loss of anti-HIV activity.

Isolation and characterization of novel cytotoxic saponins from Archidendron ellipticum.

A series of new ester saponins, elliptosides A-J, has been isolated from the tropical plant Archidendron ellipticum (Leguminosae). These saponins were particularly cytotoxic to certain renal and melanoma cancer cell lines in the NCI's 60-cell line human tumor screen. The structures of elliptosides A, E, and F were elucidated by spectroscopic and chemical means. Elliptoside A showed in vivo antitumor activity against the LOX melanoma cell line.

Novel cytotoxic, alkylated hydroquinones from Lannea welwitschii.

Two novel natural products, lanneaquinol (1) and 2'(R)-hydroxylanneaquinol (2), were isolated from the organic extract of the plant Lannea welwitschii (Hiern) Engl. Their structures were solved by spectroanalytical methods and confirmed by comparison to synthetic models. The absolute configuration of 2 was determined by the modified Mosher method. Both compounds exhibited modest cytotoxicity against the NCI panel of 60 human tumor cell lines. The structures of two isomeric 4,5-dihydroxy-5-alkyl-2-cyclohexenones (7 and 8), which appear to be biogenetic precursors of 1 and 2, were also elucidated.

Cytotoxic triterpenes from a marine sponge, Stelletta sp.

Bioassay-guided fractionation of an extract of a marine sponge, Stelletta sp., has led to the isolation and characterization of four new cytotoxic isomalabaricane triterpenes, named stellettins C (1), D (2), E (3), and F (4). Three known triterpenes (5-7) were also isolated from the same extract. The most sensitive of the tested cell lines (e.g., leukemia, central nervous system, renal) generally responded with GI50 concentrations in the low-to-mid nanomolar range.

Structure-activity modifications of the HIV-1 inhibitors (+)-calanolide A and (-)-calanolide B.

The delta 7,8 olefinic linkages within (+)-calanolide A(1) and (-)-calanolide B(2) were catalytically reduced to determine impact on the anti-HIV activity of the parent compounds. In addition, a series of structure modifications of the C-12 hydroxyl group in (-)-calanolide B was made to investigate the importance of that substituent to the HIV-1 inhibitory activity of these coumarins. A total of 14 analogs were isolated or prepared and compared to (+)-calanolide A and (-)-calanolide B in the NCI primary anti-HIV assay. While none of the compounds showed activity superior to the two unmodified leads, some structure-activity requirements were apparent from the relative anti-HIV potencies of the various analogs.

Cytotoxic falcarinol oxylipins from Dendropanax arboreus.

The crude organic extract of Dendropanax arboreus was selected as a candidate for bioassayguided fractionation on the basis of its relatively selective cytotoxicity to a subset of cell lines within the National Cancer Institute's disease-oriented in vitro tumor-screening panel. The major compound responsible for the in vitro cytotoxicity was falcarinol (1). Several other known compounds were isolated and found to be cytotoxic, including dehydrofalcarinol (2), a diyenne (3), falcarindiol (4), and dehydrofalcarindiol (5). In addition, two novel polyacetylenes, dendroarboreols A (6) and B (7), were isolated and characterized by standard and inverse-detected NMR methods. Compounds were selected from this series for absolute stereochemical determination using the modified Mosher method and preliminary in vivo evaluation using a LOX melanoma mouse xenograft model.

New pyranocoumarins isolated from Calophyllum lanigerum and Calophyllum teysmannii.

During a chemotaxonomic survey of Calophyllum extracts present in the National Cancer Institute's natural product repository, four new pyranocoumarins were isolated from extracts of C. lanigerum var. austrocoriaceum and C. teysmannii var. inophylloide (King.) P. F. Stevens (Clusiaceae). The structure elucidation and anti-HIV activity of calanolide E2 (4), cordatolide E (5), pseudocordatolide C (6), and calanolide F (9), along with a simple prenylated coumarin precursor (11), are described here.

A benzoic acid glycoside from Geniostoma antherotrichum.

Fractionation of an HIV-inhibitory organic extract of Geniostoma antherotrichum afforded a glycoside derivative, which has been characterized as 2-hydroxy-3-O-beta-D-glucopyranosyl-benzoic acid (1) on the basis of spectral analyses. The HIV-inhibitory activity of the extract was traced to polymeric tannins, while 1 was found to be inactive in the National Cancer Institute's primary anti-HIV screen.

Vasculyne, a new cytotoxic acetylenic alcohol from the marine sponge Cribrochalina vasculum.

A new C43 acetylenic alcohol, vasculyne (1), was isolated by cytotoxicity-guided fractionation of the Caribbean sponge Cribrochalina vasculum. The structure of 1 was determined by spectroscopic methods.

Antitumor activity and stereochemistry of acetylenic alcohols from the sponge Cribrochalina vasculum.

Antitumor bioassay-guided fractionation of the organic extract of the marine sponge Cribrochalina vasculum resulted in the isolation of several closely related cytotoxic acetylenic alcohols [1-8], the structures of which were assigned on the basis of chemical and spectral studies. 3-Hydroxyeicos-(4E)-en-1-yne[1], 3-hydroxydocosa-(4E,15Z)-dien-1-yne[2], 3-hydroxy-16-methyleicos-(4E)-en-1-yne[3], 3-hydroxy-19-methyleicos-(4E)-en-1-yne[4], 3-hydroxy-21-methyldocosa-(4E,15Z)-dien-1-yne [5], and 3-hydroxy-14-methyldocosa-(4E)-en-1-yne [6] are enantiomers of known compounds, while 3-hydroxyheneeicos-(4E)-en-1-yne [7] and 5-hydroxy-16-methyleicos-(3Z)-en-1-yne [8] are new metabolites isolated as minor components. The absolute configuration of C-3 in 1-7 and C-5 in 8 has been assigned as S using the modified Mosher's method. Compounds selected from this series showed selective in vitro antitumor activity against the H-522 non-small cell lung line and the IGROV-1 ovarian line. Synthetic racemic 1 demonstrated a modest dose-related therapeutic activity in a preliminary in vivo xenograft assay based on the latter cell line.