Frequent Occurrence of HIV-Inhibitory Sulphated Polysaccharides in Marine Invertebrates

Aqueous extracts of many marine invertebrates have exhibited some activity in the National Cancer Institute's primary screen for anti-HIV cytopathicity. Using a variety of techniques, including gel permeation, size exclusion and ion exchange chromatography, toluidine blue metachromicity, 13C-NMR spectroscopy and combustion analyses, we have determined that this activity is largely due to sulphated polysaccharides. Because of the wide occurrence of this class of compounds in these organisms we sought a method for the rapid dereplication of sulphated polysaccharides. It was critical that the method selected for dereplication allow differentiation of anionic polysaccharides from other AIDS-antiviral chemotypes. After evaluating a variety of methods, we found that the most efficient strategy appeared to be precipitation of the polysaccharide fraction from aqueous ethanolic solutions of the crude aqueous extracts.

Maculosin, a host-specific phytotoxin for spotted knapweed from Alternaria alternata

Several diketopiperazines have been isolated from liquid cultures of Alternaria alternata, the causal agent of black leaf blight of spotted knapweed, Centaurea maculosa Lam. One of these compounds, maculosin [the diketopiperazine cyclo(-L-Pro-L-Tyr-)], was active in the nicked-leaf bioassay at 10(-5) M; synthetic maculosin possessed chemical and biological activities identical to those of the natural product. Other diketopiperazines isolated from the fungus possessed either less activity or none at all. In tests against 19 plant species, maculosin was phytotoxic only to spotted knapweed. Thus maculosin is a host-specific phytotoxin from a weed pathogen.

Ethnobotany and drug discovery: the experience of the US National Cancer Institute

Between 1960 and 1981 the National Cancer Institute (NCI) screened 114,000 extracts of 35,000 plants, mainly collected in temperate regions. Of the three clinically active anticancer drugs so far discovered in that programme, none was isolated from a plant collected on an ethnobotanical basis, though various Taxus species, which are the source of taxol, are reported to have been used medicinally. Since 1986, the NCI has focused its collections in tropical and subtropical regions worldwide; collections cover a broad taxonomic range, though priority is given to medicinal plants when relevant information is available. As of August 1993, 21,881 extracts derived from over 10,500 samples had been tested in a screen for activity against the human immunodeficiency virus (HIV); 2320 of these extracts were of medicinal plant origin. Approximately 18% of both the total number of extracts and the medicinal plant-derived extracts showed significant anti-HIV activity; in each instance about 90% of the active extracts were aqueous. The activity of the aqueous extracts has been attributed mainly to the presence of polysaccharides or tannins. Four plant-derived compounds are in preclinical development at the NCI; only one of the four sources plants, obtained from a noncontract source, was collected on an ethnobotanical basis. At this stage the results indicate that the current NCI collection policy offers the best chances for the discovery and development of agents for the treatment of AIDS (acquired immune deficiency syndrome) and cancer.

Absolute stereochemistry and anti-HIV activity of minquartynoic acid, a polyacetylene from Ochanostachys amentacea

Anti-HIV bioassay-guided fractionation of an organic extract of Ochanostachys amentacea provided an HIV-inhibitory polyacetylenic acid. The identity of this compound was established as (-)-17-hydroxy-9,11,13,15-octadecatetraynoic acid (1), also known as minquartynoic acid, by comparison of its physical and spectral data with previously reported values. Analysis of Mosher's ester derivatives of the methyl ester of 1 allowed assignment of S absolute stereochemistry to the lone chiral center. In an in vitro XTT-based anti-HIV assay, 2-5 micrograms/mL of minquartynoic acid (1) effectively inhibited human lymphoblastoid cell killing by HIV-1.

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.

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.

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).

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.

Guttiferone F, the first prenylated benzophenone from Allanblackia stuhlmannii

The HIV-inhibitory activity in extracts of Allanblackia stuhlmannii was tracked, via bioassay-guided fractionation, to a new member of the camboginol/guttiferone class of prenylated benzophenones, guttiferone F (1). The structure was solved by extensive NMR analyses and by acid-catalyzed conversion to 30-epi-cambogin (4). This is the first report of this compound type in the genus Allanblackia.

Isolation and characterization of adociavirin, a novel HIV-inhibitory protein from the sponge Adocia sp

Aqueous extracts of the New Zealand sponge Adocia sp. (Haplosclerida) displayed potent anticytopathic activity in CEM-SS cells infected with HIV-1. Protein fractions of the extract bound both to the viral coat protein gp120 and to the cellular receptor CD4, but not to other tested proteins. The purified active protein, named adociavirin, was characterized by isoelectric focusing, amino acid analysis, MALDI-TOF mass spectrometry and N-terminal sequencing. Adociavirin, a disulfide-linked homodimer with a native molecular weight of 37 kDa, was active against diverse strains and isolates of HIV-1, as well as HIV-2, with EC50 values ranging from 0.4 nM to > 400 nM. The anti-HIV potency of adociavirin appears dependent on host cell type, with macrophage cultures being the most sensitive and peripheral blood lymphocytes the most resistant.

Korundamine A, a novel HIV-inhibitory and antimalarial "hybrid" naphthylisoquinoline alkaloid heterodimer from Ancistrocladus korupensis

A unique heterodimeric naphthylisoquinoline alkaloid, korundamine A (2), comprised of two different monomeric biaryl halves, has been isolated from the Cameroonian tropical liana Ancistrocladus korupensis. Korundamine A is the first "hybrid" dimer found in the Ancistrocladaceae; in vitro, it demonstrated anticytopathic activity against HIV-1 and antimalarial activity against Plasmodium falciparum.

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.

Michellamines D-F, new HIV-inhibitory dimeric naphthylisoquinoline alkaloids, and korupensamine E, a new antimalarial monomer, from Ancistrocladus korupensis

New monomeric (korupensamine E, 6) and dimeric (michellamines D-F, 7-9) naphthylisoquinoline alkaloids have been isolated from exracts of the tropical liana Ancistrocladus korupensis. Structures were determined by spectroanalytical methods, and stereochemistry was defined through NOE correlations, chemical degradation, and CD spectroscopy. Michellamines D-F exhibited in vitro HIV-inhibitory activity comparable to michellamine B, and korupensamine E exhibited in vitro antimalarial activity comparable to korupensamines A-D.

Discovery of cyanovirin-N, a novel human immunodeficiency virus-inactivating protein that binds viral surface envelope glycoprotein gp120: potential applications to microbicide development

We have isolated and sequenced a novel 11-kDa virucidal protein, named cyanovirin-N (CV-N), from cultures of the cyanobacterium (blue-green alga) Nostoc ellipsosporum. We also have produced CV-N recombinantly by expression of a corresponding DNA sequence in Escherichia coli. Low nanomolar concentrations of either natural or recombinant CV-N irreversibly inactivate diverse laboratory strains and primary isolates of human immunodeficiency virus (HIV) type 1 as well as strains of HIV type 2 and simian immunodeficiency virus. In addition, CV-N aborts cell-to-cell fusion and transmission of HIV-1 infection. Continuous, 2-day exposures of uninfected CEM-SS cells or peripheral blood lymphocytes to high concentrations (e.g., 9,000 nM) of CV-N were not lethal to these representative host cell types. The antiviral activity of CV-N is due, at least in part, to unique, high-affinity interactions of CV-N with the viral surface envelope glycoprotein gp120. The biological activity of CV-N is highly resistant to physicochemical denaturation, further enhancing its potential as an anti-HIV microbicide.

Isolation and characterization of niphatevirin, a human-immunodeficiency-virus-inhibitory glycoprotein from the marine sponge Niphates erecta

Anti-human immunodeficiency virus (HIV)-bioassay-guided fractionation of aqueous extracts of the Caribbean sponge Niphates erecta led to isolation of a novel anti-HIV protein, named niphatevirin. The protein was purified to homogeneity by ethanol precipitation, ammonium sulfate precipitation, gel-permeation chromatography and concanavalin-A-Sepharose affinity chromatography. Niphatevirin potently inhibited the cytopathic effects of HIV-1 infection in cultured human lymphoblastoid (CEM-SS) cells; the effective concentration of drug that results in 50% protection of the cells through inhibition of cell lethality, cell-cell fusion and syncytium formation was approximately 10 nM. Delay of addition of niphatevirin to infected cultures by two hours markedly decreased (approximately 50%) cytoprotection; delay of addition by eight hours resulted in no antiviral activity. Niphatevirin bound to CD4 in a manner that prevented the binding of gp120, but did not directly bind gp120. Niphatevirin (6.5 microM) was inactive in both hemagglutination and hemolysis assays. Niphatevirin had a molecular mass of about 19 kDa by matrix-assisted laser-desorption ionization-time of flight (MALDI-TOF) mass spectrometry, and a native molecular mass of approximately 18 kDa by gel-filtration chromatography. The protein had an acidic isoelectric point of 4.2-4.6, and was shown by periodate acid Schiff's staining to be glycosylated.

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.

HIV inhibitory natural products. 26. Quinoline alkaloids from Euodia roxburghiana

Bioassay-directed fractionation of the CH2Cl2-MeOH extract of Euodia roxburghiana resulted in the isolation of two known quinoline alkaloids, buchapine (1) and 2, and three new furoquinoline alkaloids, roxiamines A, B, and C (3-5). Compounds 1 and 2 protected CEM-SS cells from the cytopathic effects of HIV-1 in vitro (EC50 0.94 and 1.64 microM, respectively), but 3-5 were inactive against HIV-1.

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.

Majapolene A, a cytotoxic peroxide, and related sesquiterpenes from the red alga Laurencia majuscula

Seven new sesquiterpenes, majapolenes A [1] and B [2], majapolone [3], and majapols A [4], B [5], C [6], and D [7], were isolated from a Philippine collection of Laurencia majuscula. With the exception of majapolene B [2], all compounds were isolated as inseparable diastereomeric mixtures. Structure elucidation was achieved by spectroscopic methods. Majapolene A [1], a dioxabicyclo[2.2.2]-alkene, displayed modest activity in the NCI 60-cell line cytotoxicity screen. Majapolene A was also found as a major component of a Philippine collection of Laurencia caraibica.

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.

A reinvestigation of Maprounea triterpenes

Anti-HIV activity and the inhibition of phorbol ester receptor binding activity in two species of Maprounea were traced to small amounts of highly potent phorbol esters of the daphnane type. The triterpenes previously isolated from this genus were found to be devoid of biological activity when scrupulously purified. Four new triterpene esters were elucidated; two [3,4] were found in M. africana, while three [4,6,7] were found in M. membranacea. Nmr assignments have also been made for two previously known compounds [2,5] in this group.

Mycalolides D and E, new cytotoxic macrolides from a collection of the stony coral Tubastrea faulkneri

Fractionation of a cytotoxic extract of the stony coral Tubastrea faulkneri yielded a series of cytotoxic polyoxazole macrolides and several noncytotoxic indole derivatives. Two new macrolides, mycalolides D [1] and E [2], were isolated and identified, in addition to the known compound mycalolide C [3]. The macrolide structures were elucidated by detailed analysis of their spectroscopic data and by comparison with related compounds.

The pseudocalanolides: structure revision of calanolides C and D

Nmr spectra of synthetic structures corresponding to those initially reported for natural compounds calanolide C [1] and calanolide D [2] showed some subtle differences from those of the natural products. Further analysis has resulted in revision of the structures of the natural compounds, now renamed pseudocalanolides C [3] and D [4]. The absolute stereochemistry of pseudocalanolide C was established as [6S, 7S, 8R] using the modified Mosher's method.

A novel phorbol ester from Excoecaria agallocha

The novel phorbol ester 12-deoxyphorbol 13-(3E,5E-decadienoate) [1] was isolated as the anti-HIV principle of Excoecaria agallocha leaves and stems collected in northwest Australia. The structure was determined by spectral means. Compound 1 was also a potent displacer of [3H]-phorbol dibutyrate from rat brain membranes.

Patellamide F, A new cytotoxic cyclic peptide from the colonial ascidian Lissoclinum patella

Cytotoxicity-directed fractionation of an organic extract of the tunicate Lissoclinum patella afforded a new cyclic octapeptide, patellamide F [1]. The structure and absolute stereochemistry of 1 were established by a combination of spectroscopic and chemical methods. Three known cyclic peptides, patellamide B [2], ulithiacyclamide, and lissoclinamide 3, were also isolated and identified.

Preparative separation of naphthyltetrahydroisoquinoline alkaloids from Ancistrocladus korupensis by centrifugal partition chromatography

Crude extracts of Ancistrocladus korupensis contain a complex mixture of naphthyltetrahydroisoquinoline alkaloids, including the human immunodeficiency virus-inhibitory dimeric alkaloids michellamines A and B and the antimalarial monomeric korupensamines A-D. The efficient separation of michellamines A and B from these extracts has been accomplished by centrifugal partition chromatography. The chromatographic conditions used on a multi-channel cartridge unit (Sanki LLN) have been successfully scaled up with a newly developed, stacked-disk type centrifugal partition chromatography unit (Sanki NMF) for separating larger amounts of alkaloid mixtures with similar resolution. A refined, three-step process (solvent-solvent partitioning, centrifugal partition chromatography and HPLC) has been developed and applied to the scaled-up production of michellamine B for preclinical drug development.

Isolation and structure/activity features of halomon-related antitumor monoterpenes from the red alga Portieria hornemannii

Ten halogenated monoterpenes (2-6 and 8-12) related to the novel antitumor compound halomon (1) or to the carbocyclic analog 7 have been isolated from different geographic collections of the red alga, Portieria hornemannii. Structures were assigned to the basis of spectral analyses (primarily NMR and MS). The absolute configuration of isohalomon (2) was further established by X-ray crystallography. The compounds were comparatively evaluated alongside 1 and 7 in the U.S. National Cancer Institute's in vitro human tumor cell line screening panel. The results provide some interesting initial insights into the structure/activity relationships in this series.

Novel naphthoquinones from Conospermum incurvum

During the reisolation of the trimeric naphthoquinone derivative conocurvone [1] from an extract of the Australian shrub Conospermum incurvum, six monomeric naphthoquinones were isolated. These include three novel 1,4-naphthoquinone derivatives: 3-methyl-14,15-dihydro-15-hydroxyteretifolione B [3], 3-methyl-14,15-dihydro-15-hydroxyteretifolione B methyl ether [4], and 2,3-dimethyl-6-hydroxy-7-methoxy-1,4-naphthoquinone [5]. In addition, the previously reported compounds 3-methylteretifolione B [6], 3-methylteretifolione B methyl ether [7], and 8-geranyl-2,7-dihydroxy-3-methyl-1,4-naphthoquinone [8] were isolated and identified. The structures of the novel 1,4-naphthoquinones were elucidated by spectral methods. While conocurvone [1] is a potent inhibitor of HIV-1-induced cell killing, all of the monomeric naphthoquinone derivatives were inactive against HIV-1.

Cucurbitacins: differential cytotoxicity, dereplication and first isolation from Gonystylus keithii

A characteristic pattern of differential cytotoxicity of extracts of Iberis amara seeds, predominantly toward renal tumor, brain tumor, and melanoma cell lines in the NCI human disease-oriented tumor screening panel, was traced to cucurbitacins E [1] and I [2]. This same differential cytotoxicity profile was detected in extracts of Begonia plebeja and Gonystylus keithii. Computer-assisted recognition of these profiles was followed by a rapid chemical fractionation, thus permitting the efficient dereplication of those extracts containing cucurbitacins B [3] and D [4], respectively. This is the first report of cucurbitacins from the genus Gonystylus.

Anti-HIV michellamines from Ancistrocladus korupensis

Here we report details of the isolation and determination of the absolute configurations and comparative anti-HIV activities of novel, atropisomeric naphthylisoquinoline alkaloid dimers, michellamines A, B, and C, from a newly described species of Ancistrocladus from the Korup rainforest of Cameroon. We further provide a more extensive analysis of the range of anti-HIV activity of michellamine B, the most potent and abundant member of the series. Michellamine B inhibited HIV-induced cell killing and viral replication in a variety of human cell lines, as well as in cultures of human peripheral blood leukocytes and monocytes. Michellamine B was active against a panel of biologically diverse laboratory and clinical strains of HIV-1, including the AZT-resistant strain G910-6 and the pyridinone-resistant strain A17; the compound also inhibited several strains of HIV-2.

HIV-inhibitory natural products. 11. Comparative studies of sulfated sterols from marine invertebrates

A total of 22 sulfated sterols isolated from marine sponges, ophiuroids (brittle stars), and asteroids (sea stars) were comparatively evaluated for their antiviral activity against HIV-1 and HIV-2. In general, sterols with sulfate groups at position 2, 3, or 6 were the most active, with EC50 values of 3-13 microM against HIV-1 (RF) and 2-8 microM against HIV-2 (CBL20). Those compounds which were sulfated on the sterol D ring were completely inactive against both HIV-1 and HIV-2. Overall, sulfated sterols active against HIV-1 were also active against HIV-2.

Koumbalones A and B, new casbane diterpenes from Maprounea africana

The organic extract of Maprounea africana yielded koumbalones A [1] and B [2], defined by spectral methods as new variations on the casbane ring system. The gross structures, relative configurations, and solution conformations were determined by a combination of spectral analyses and molecular modeling. Because koumbalone A spontaneously converts to koumbalone B at room temperature, koumbalone B may be an artifact of isolation.

A cytotoxic beta-carboline from the bryozoan Catenicella cribraria

1-Vinyl-8-hydroxy-beta-carboline was identified as the cytotoxic constituent of the bryozoans Catenicella cribraria and Cribricellina cribraria. Literature nmr data for this previously known compound, now reported from a new source, were corrected.

Two new cytotoxic chalcones from Calythropsis aurea

The crude extract of Calythropsis aurea (Myrtaceae) produced a pattern of differential cytotoxicity in the NCI 60 cell line assay which was similar to those of known tubulin-interactive compounds. Cytotoxicity-guided fractionation led to the isolation of two new chalcones, calythropsin [1] and dihydrocalythropsin [2], which were responsible for the activity. Calythropsin was demonstrated to have a weak effect on mitosis, and presumably also on tubulin polymerization.

A chemical screening strategy for the dereplication and prioritization of HIV-inhibitory aqueous natural products extracts

A relatively high percentage (ca. 15%) of aqueous extracts from terrestrial plants, cyanobacteria, and marine invertebrates and algae has exhibited activity in the National Cancer Institute's primary AIDS-antiviral screen. By removal of anionic polysaccharides in a first stage of dereplication, we have eliminated from further consideration a considerable number of these extracts. However, a still substantial proportion of the active extracts remained, from which we wished to select and prioritize a small percentage for our detailed bioassay-directed fractionation studies. Therefore, a chemical screening protocol, utilizing various solid-phase extraction cartridges, has been developed for a second-stage dereplication and to assist in prioritization of these extracts for our further investigations.

A pentahalogenated monoterpene from the red alga Portieria hornemannii produces a novel cytotoxicity profile against a diverse panel of human tumor cell lines

A polyhalogenated acyclic monoterpene, 6(R)-bromo-3(S)-(bromomethyl)-7- methyl-2,3,7-trichloro-1-octene (1) was obtained as a major component of the organic extract of the red alga Portieria hornemannii. X-ray diffraction analysis provided the complete structure, including correct placement of the different halogen atoms and determination of the absolute stereochemistry. Detailed NMR analyses provided complete 1H and 13C assignments. Compound 1 exhibited highly differential cytotoxicity against the U.S. National Cancer Institute's new in vitro human tumor cell line screening panel; brain tumor, renal, and colon tumor cell lines were most sensitive to 1, while leukemia and melanoma lines were relatively less sensitive. A second collection of P. hornemanni yielded the novel, monocyclic 2, considerably less cytotoxic and devoid of differential activity. On the basis of its unprecedented cytotoxicity profile in the NCI primary screen, compound 1 has been selected by the NCI Decision Network Committee for preclinical drug development.

The calanolides, a novel HIV-inhibitory class of coumarin derivatives from the tropical rainforest tree, Calophyllum lanigerum

Eight new coumarin compounds (1-8) were isolated by anti-HIV bioassay-guided fractionation of an extract of Calophyllum lanigerum. The structures of calanolide A (1), 12-acetoxycalanolide A (2), 12-methoxycalanolide A (3), calanolide B (4), 12-methoxycalanolide B (5), calanolide C (6) and related derivatives 7 and 8 were solved by extensive spectroscopic analyses, particularly HMQC, HMBC, and difference NOE NMR experiments. The absolute stereochemistry of calanolide A (1) and calanolide B (4) was established by a modified Mosher's method. Calanolides A (1) and B (4) were completely protective against HIV-1 replication and cytopathicity (EC50 values of 0.1 microM and 0.4 microM, respectively), but were inactive against HIV-2. Some of the related compounds also showed evidence of anti-HIV-1 activity. Studies with purified bacterial recombinant reverse transcriptases (RT) revealed that the calanolides are HIV-1 specific RT inhibitors. Moreover, calanolide A was active not only against the AZT-resistant G-9106 strain of HIV-1 but also against the pyridinone-resistant A17 strain. This was of particular interest since the A17 virus is highly resistant to previously known HIV-1 specific, non-nucleoside RT inhibitors (e.g., TIBO; BI-RG-587; L693,593) which comprise a structurally diverse but apparently common pharmacologic class. The calanolides represent a substantial departure from the known class and therefore provide a novel new anti-HIV chemotype for drug development.

A nonpromoting phorbol from the samoan medicinal plant Homalanthus nutans inhibits cell killing by HIV-1

Extracts of Homalanthus nutans, a plant used in Samoan herbal medicine, exhibited potent activity in an in vitro, tetrazolium-based assay which detects the inhibition of the cytopathic effects of human immunodeficiency virus (HIV-1). The active constituent was identified as prostratin, a relatively polar 12-deoxyphorbol ester. Noncytotoxic concentrations of prostratin from greater than or equal to 0.1 to greater than 25 microM protected T-lymphoblastoid CEM-SS and C-8166 cells from the killing effects of HIV-1. Cytoprotective concentrations of prostratin greater than or equal to 1 microM essentially stopped virus reproduction in these cell lines, as well as in the human monocytic cell line U937 and in freshly isolated human monocyte/macrophage cultures. Prostratin bound to and activated protein kinase C in vitro in CEM-SS cells and elicited other biochemical effects typical of phorbol esters in C3H10T1/2 cells; however, the compound does not appear to be a tumor promoter. In skin of CD-1 mice, high doses of prostratin induced ornithine decarboxylase only to 25-30% of the levels induced by typical phorbol esters at doses 1/30 or less than that used for prostratin, produced kinetics of edema formation characteristic of the nonpromoting 12-deoxyphorbol 13-phenylacetate, and failed to induce the acute or chronic hyperplasias typically caused by tumor-promoting phorbols at doses of 1/100 or less than that used for prostratin.