10-Demethoxystegane, a new lignan from Steganotaenia araliacea.

A new dibenzocyclooctadiene lactone lignan, 10-demethoxystegane (1), together with the known compounds steganone (2) and prestegane B (3), have been isolated from the organic extract of Steganotaenia araliacea(Apiaceae). Steganone (2) showed antiproliferative activity against an ovarian cancer cell line (OVCAR-3).

A novel anti-HIV macrocyclic peptide from Palicourea condensata.

A 37 amino acid cyclic polypeptide has been isolated from the organic extract of the tropical tree Palicourea condensata. Palicourein (1) is the largest of a growing family of plant peptides that contain a cyclized amino acid backbone cross-linked via three internal disulfide bridges. Palicourein inhibits the in vitro cytopathic effects of HIV-1RF infection of CEM-SS cells with an EC50 value of 0.1 microM and an IC50 value of 1.5 microM.

Thorectandrols A and B, new cytotoxic sesterterpenes from the marine sponge Thorectandra species.

Two new sesterterpenes, thorectandrol A (1) and B (2), were isolated from extracts of the marine sponge Thorectandra sp. The structures were determined by extensive NMR spectral data analysis. NOE correlations were used to define the relative stereochemistry of 1 and 2, while CD data were used to suggest their absolute stereochemistry. Both compounds 1 and 2 inhibited the growth of MALME-3M (melanoma) and MCF-7 (breast) cancer cell lines in the range 30-40 microg/mL. The known compound palauolol (3) was isolated as well and was also cytotoxic.

Anti-HIV prenylated flavonoids from Monotes africanus.

Six flavonoids, among them a new dihydroflavonol, 6,8-diprenylaromadendrin (1), and the flavonol 6,8-diprenylkaempferol (3), have been isolated from the organic extract of Monotes africanus. The isolated compounds containing a 5,7-dihydroxy-6,8-diprenyl system in the A ring of the flavonoid (1, 3, and 6) exhibited HIV-inhibitory activity in the XTT-based, whole-cell screen. In addition, several (13)C NMR assignments of lonchocarpol A (6) were corrected.

New cytotoxic isomalabaricane triterpenes from the sponge Jaspis species.

Three new isomalabaricane triterpenes, 29-hydroxystelliferin E (1), 29-hydroxystelliferin A (2), and stelliferin G (3), together with the known triterpene 3-epi-29-hydroxystelliferin E (4), were isolated from the organic extract of the sponge Jaspis sp. collected in the South Pacific. All the compounds isolated showed antiproliferative activity against melanoma cells (MALME-3M).

Discovery of a novel antitumor benzolactone enamide class that selectively inhibits mammalian vacuolar-type (H+)-atpases.

A series of naturally occurring compounds reported recently by multiple laboratories defines a new small-molecule class sharing a unique benzolactone enamide core structure and diverse biological actions, including inhibition of growth of tumor cells and oncogene-transformed cell lines. Here we show that representative members of this class, including salicylihalamide A, lobatamides A-F, and oximidines I and II inhibit mammalian vacuolar-type (H+)-ATPases (V-ATPases) with unprecedented selectivity. Data derived from the NCI 60-cell antitumor screen critically predicted the V-ATPase molecular target, while specific biochemical assays provided confirmation and further illumination. The compounds potently blocked representative V-ATPases from human kidney, liver, and osteoclastic giant-cell tumor of bone but were essentially inactive against V-ATPases of Neurospora crassa and Saccharomyces cerevisiae and other membrane ATPases. Essential regulation of pH in cytoplasmic, intraorganellar, and local extracellular spaces is provided by V-ATPases, which are ubiquitously distributed among eukaryotic cells and tissues. The most potent and selective V-ATPase inhibitors heretofore known were the bafilomycins and concanamycins, which do not discriminate between mammalian and nonmammalian V-ATPases. Numerous physiological processes are mediated by V-ATPases, and aberrant V-ATPase functions are implicated in many different human diseases. Previous efforts to develop therapeutic pharmacological modulators of V-ATPases have been frustrated by a lack of synthetically tractable and biologically selective leads. Therefore, availability of the unique benzolactone enamide inhibitor class may enable further elucidation of functional and architectural features of mammalian versus nonmammalian V-ATPase isoforms and provide new opportunities for targeting V-ATPase-mediated processes implicated in diverse pathophysiological phenomena, including cancer.

Isolation and characterization of Myrianthus holstii lectin, a potent HIV-1 inhibitory protein from the plant Myrianthus holstii(1).

Aqueous extracts from the African plant Myrianthus holstii potently inhibited the infection of the T-lymphoblastoid cell line, CEM-SS, by human immunodeficiency virus-1(RF) (HIV-1(RF)). The active constituent, M. holstii lectin (MHL), was purified by LH-20 column chromatography and reversed phase HPLC. MHL, a 9284-Da cysteine-rich protein, was characterized by amino acid analysis, N-terminal sequencing, ESIMS, and matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry. Pure MHL had anti-HIV activity, with an EC(50) value of 150 nM. Delaying the addition of MHL for up to 8 h after initial exposure of CEM-SS cells to virus did not result in loss of the antiviral activity; however, if addition of the compound was delayed for 16 h or more, there was a marked decrease in the antiviral activity. MHL bound to a virus-free, soluble form of the viral envelope protein gp120 but did not inhibit the subsequent binding to a cell-free, soluble form of the cellular receptor CD4.

Siamenol, a new carbazole alkaloid from Murraya siamensis.

A new carbazole alkaloid, siamenol (1), and two known alkaloids, mahanimbine (2) and mahanimbilol (3), have been isolated from the organic extract of Murraya siamensis. The novel compound exhibited HIV-inhibitory activity.

Laxifloranone, a new phloroglucinol derivative from Marila laxiflora.

A new polyisoprenylated phloroglucinol derivative has been isolated from the twigs of Marila laxiflora and characterized on the basis of 1D and 2D NMR spectra. Laxifloranone (1) shows moderate inhibition of the cytopathic effects of in vitro HIV infection.

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.

Pyranocoumarins from tropical species of the genus Calophyllum: a chemotaxonomic study of extracts in the National Cancer Institute collection.

(+)-Calanolide A, a novel dipyranocoumarin from the Malesian tree Calophyllum lanigerum var. austrocoriaceum, and a closely related compound, (-)-calanolide B, isolated from Calophyllum teysmannii var. inophylloide, are representatives of a distinct class of nonnucleoside HIV-1 specific reverse-transcriptase inhibitor under development as an AIDS chemotherapeutic. NCI repository specimens totalling 315 organic extracts from 31 taxa of Calophyllum were analyzed for related pyranocoumarins using a simple TLC system. A total of 127 extracts was initially classified as "positive"; eight out of the 31 taxa examined, representing perhaps 28 species already described (1/7-1/8 of all the species in this genus), contained prenylated coumarins, suggesting that these compounds, while sometimes abundantly present, are not widespread in the genus. Representative members of the TLC-positive extracts were partitioned between CH2C12 and 25% aqueous MeOH; the CH2C12-soluble materials were then analyzed by TLC and 1H NMR to confirm the presence of pyranocoumarins. The anti-HIV activity of the partitioned extracts are also presented. This study suggested that there are several distinctive coumarin chemotaxonomic markers distinguishing species of this genus.

Isolation and characterization of new anti-HIV and cytotoxic leads from plants, marine, and microbial organisms.

New cytotoxic isomalabaricane triterpenes have been isolated from a sponge Stelletta sp. (1-7); anti-HIV pterocarpans (8 and 9) and isoflavanoids (12-16 and 18) were elucidated from two tropical plants in the genus Erythrina; and anti-HIV enniatins (20 and 22-23) were characterized from fungi in the genera Fusarium and Alternaria. The enniatins were evaluated for in vivo anti-HIV activity in the hollow fiber assay.

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.

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.

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.

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.

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.