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.

New cytotoxic N-methylated beta-carboline alkaloids from the marine ascidian Eudistoma gilboverde

Bioassay-guided fractionation of an extract of the marine ascidian Eudistoma gilboverde provided three new beta-carboline alkaloids identified as 2-methyleudistomin D (1), 2-methyleudistomin J (2), and 14-methyleudistomidin C (3). Six known metabolites, eudistomins C, D (4), E, J (5), K, and L, were also isolated and characterized. The structures of the new metabolites were elucidated by spectroscopic analyses and by comparison of their spectral data with related literature values. Of the three new compounds, 14-methyleudistomidin C (3) exhibited the most potent cytotoxic activity with IC(50)'s of < 1.0 microg/mL against four different human tumor cell lines.

Chondropsin D, a new 37-membered-ring macrolide lactam from the marine sponge Chondropsis species

Chondropsin D (2), a new 37-membered-ring macrolide lactam, was isolated as a minor constituent of an aqueous extract of the marine sponge Chondropsis sp. This sponge sample had previously been the source of chondropsins A (1) and B, two novel polyketide-derived macrolides with potent cytotoxic activity. The structure of 2 was initially deduced from analysis of spectral data. This assignment was supported by the observation that chondropsin A (1), which contains a 35-membered macrocyclic ring, could be converted to chondropsin D (2) by a base-catalyzed intramolecular transesterification reaction. Rearrangement of the methylated derivative of chondropsin A (3) to the corresponding methylated analogue of chondropsin D (4) confirmed the structure of 2.

A new isoquinoline alkaloid from the marine sponge Haliclona species

Two isoquinoline alkaloids, including the new compound 1, were isolated from the cytotoxic fractions of an aqueous extract of the marine sponge Haliclona sp. The structures of these compounds were established as 1-hydroxymethyl-7-methoxyisoquinolin-6-ol (1) and mimosamycin (2) by conventional spectroscopic methods and by comparison with related compounds. Mimosamycin (2) was the principal cytotoxin with an IC(50) of approximately 10 microg/mL against melanoma and ovarian human tumor cell lines.

Microspinosamide, a new HIV-inhibitory cyclic depsipeptide from the marine sponge Sidonops microspinosa

Microspinosamide (1), a new cyclic depsipeptide incorporating 13 amino acid residues, was isolated from extracts of an Indonesian collection of the marine sponge Sidonops microspinosa. Its structure was elucidated by extensive NMR and mass spectral analyses, and by chemical degradation and derivatization studies. The tridecapeptide 1 incorporates numerous uncommon amino acids, and it is the first naturally occurring peptide to contain a beta-hydroxy-p-bromophenylalanine residue. Microspinosamide (1) inhibited the cytopathic effect of HIV-1 infection in an XTT-based in vitro assay with an EC(50) value of approximately 0.2 microg/mL.

Stolonic acids A and B, new cytotoxic cyclic peroxides from an Indian Ocean ascidian Stolonica species

Two new 3,6-epidioxy-7,10-tetrahydrofurano C(26) unsaturated fatty acids, stolonic acids A (1) and B (2), were isolated from a previously undescribed ascidian species, Stolonica sp. collected off the Maldive Islands in the Indian Ocean. The structures and relative stereochemistry of 1 and 2 were determined using conventional spectroscopic methods. Both compounds exhibited antiproliferative activity against selected human melanoma and ovarian tumor cell lines, with IC(50) values of approximately 0.05-0.1 microg/mL.

Haligramides A and B, two new cytotoxic hexapeptides from the marine sponge Haliclona nigra

Bioassay-guided fractionation of a cytotoxic aqueous extract of the sponge Haliclona nigra provided two new cyclic hexapeptides, haligramides A (1) and B (2), in addition to the known peptide, waiakeamide (3). The structures of peptides 1 and 2 were elucidated by extensive NMR analyses and by comparison of their spectral data with those of waiakeamide (3). The identity of haligramide A (1) was confirmed by its oxidative conversion to waiakeamide (3). Further structural confirmation was provided by oxidation of peptides 1, 2, and 3 to the common bis-sulfone derivative 4.

HIV-inhibitory cembrane derivatives from a Philippines collection of the soft coral Lobophytum species

Bioassay-guided fractionation of an aqueous extract of a Philippine Islands collection of the soft coralLobophytum sp. concentrated its HIV-inhibitory activity into fractions rich in cembranoid diterpenes. Lobohedleolide (1), (7Z)-lobohedleolide (2), and a new compound, 17-dimethylaminolobohedleolide (3), were purified from these fractions by HPLC. The structures of compounds 1-3 were elucidated by spectroscopic analyses and by comparison of their spectral data with previously reported values. The relative stereochemistry of the gamma-lactone ring substituents of 3 was determined by 1D NOESY experiments. While several other cembranoids that contain a dimethylamino functional group have been reported from the soft coral Sinularia sp., compound 3 represents the first cembrane diterpene with this functional group isolated from a Lobophytum species. Diterpenoids 1-3 exhibited moderate HIV-inhibitory activity (EC(50) approximately 3-5 microg/mL) in a cell-based in vitro anti-HIV assay.

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.

Crystal structure of cyanovirin-N, a potent HIV-inactivating protein, shows unexpected domain swapping

The crystal structure of cyanovirin-N (CV-N), a protein with potent antiviral activity, was solved at 1.5 A resolution by molecular replacement using as the search model the solution structure previously determined by NMR. The crystals belong to the space group P3221 with one monomer of CV-N in each asymmetric unit. The primary structure of CV-N contains 101 residues organized in two domains, A (residues 1 to 50) and B (residues 51 to 101), with a high degree of internal sequence and structural similarity. We found that under the conditions of the crystallographic experiments (low pH and 26 % isopropanol), two symmetrically related monomers form a dimer by domain swapping, such that domain A of one monomer interacts with domain B' of its crystallographic symmetry mate and vice versa. Because the two swapped domains are distant from each other, domain swapping does not result in additional intramolecular interactions. Even though one of the protein sample solutions that was used for crystallization clearly contained 100 % monomeric CV-N molecules, as judged by various methods, we were only able to obtain crystals containing domain-swapped dimers. With the exception of the unexpected phenomenon of domain swapping, the crystal structure of CV-N is very similar to the NMR structure, with a root-mean-square deviation of 0.55 A for the main-chain atoms, the best agreement reported to date for structures solved using both techniques.

Solution structure by NMR of circulin A: a macrocyclic knotted peptide having anti-HIV activity

The three-dimensional solution structure of circulin A, a 30 residue polypeptide from the African plant Chassalia parvifolia, has been determined using two-dimensional 1H-NMR spectroscopy. Circulin A was originally identified based upon its inhibition of the cytopathic effects and replication of the human immunodeficiency virus. Structural restraints consisting of 369 interproton distances inferred from nuclear Overhauser effects, and 21 backbone dihedral and nine chi1 angle restraints from spin-spin coupling constants were used as input for simulated annealing calculations and energy minimisation in the program X-PLOR. The final set of 12 structures had mean pairwise rms differences over the whole molecule of 0.91 A for the backbone atom, and 1.68 A for all heavy atoms. For the well-defined region encompassing residues 2-12 and 18-27, the corresponding values were 0.71 and 1.66 A, respectively. Circulin A adopts a compact structure consisting of beta-turns and a distorted segment of triple-stranded beta-sheet. Fluorescence spectroscopy provided additional evidence for a solvent-exposed Trp residue. The molecule is stabilised by three disulfide bonds, two of which form an embedded loop completed by the backbone fragments connecting the cysteine residues. A third disulfide bond threads through the centre of this loop to form a "cystine-knot" motif. This motif is present in a range of other biologically active proteins, including omega-contoxin GVIA and Cucurbita maxima trypsin inhibitor. Circulin A belongs to a novel class of macrocyclic peptides which have been isolated from plants in the Rubiaceae family. The global fold of circulin A is similar to kalata B1, the only member of this class for which a structure has previously been determined.

Solution structure of cyanovirin-N, a potent HIV-inactivating protein

The solution structure of cyanovirin-N, a potent 11,000 Mr HIV-inactivating protein that binds with high affinity and specificity to the HIV surface envelope protein gp120, has been solved by nuclear magnetic resonance spectroscopy, including extensive use of dipolar couplings which provide a priori long range structural information. Cyanovirin-N is an elongated, largely beta-sheet protein that displays internal two-fold pseudosymmetry. The two sequence repeats (residues 1-50 and 51-101) share 32% sequence identity and superimpose with a backbone atomic root-mean-square difference of 1.3 A. The two repeats, however, do not form separate domains since the overall fold is dependent on numerous contacts between them. Rather, two symmetrically related domains are formed by strand exchange between the two repeats. Analysis of surface hydrophobic clusters suggests the location of potential binding sites for protein-protein interactions.

Recombinant production of cyanovirin-N, a potent human immunodeficiency virus-inactivating protein derived from a cultured cyanobacterium

Here we describe the recombinant production and purification of a novel anti-human immunodeficiency virus (HIV) protein, cyanovirin-N (CV-N), in Escherichia coli. Initial attempts to express CV-N using a vector containing an ompA signal peptide sequence resulted in production of an intractable mixture of the full-length (101 amino acid residue) protein and a truncated form lacking the first two N-terminal amino acids. The truncated protein was observed regardless of the host cell line, culture conditions, or induction time. These observations suggested that an as yet unidentified protease or peptidase was responsible for proteolytic cleavage between the second and third N-terminal amino acids of CV-N when presented as an ompA-CV-N fusion protein. When the ompA signal peptide sequence was replaced by a pelB signal peptide sequence, CV-N was produced in high yield as a single, homogeneous protein. This was confirmed by electrospray ionization mass spectrometry and N-terminal sequencing. This expression system provides a basis for large-scale production of clinical grade CV-N for further research and development as an anti-HIV microbicide.

Construction and enhanced cytotoxicity of a [cyanovirin-N]-[Pseudomonas exotoxin] conjugate against human immunodeficiency virus-infected cells

Cyanovirin-N (CV-N) is a novel 11-kDa anti-HIV(human immunodeficiency virus) protein that binds with high affinity to the viral envelope glycoprotein gp120. In contrast to soluble CD4 and most known neutralizing antibodies that bind gp120, CV-N exerts potent anti-viral activity against primary clinical HIV isolates as well as laboratory-adapted strains of HIV. Here we describe the recombinant production, purification, and characterization of a chimeric toxin molecule, FLAG-CV-N-PE38, that contains CV-N as a gp120-targeting moiety linked to the translocation and cytotoxic domains of Pseudomonas exotoxin A. FLAG-CV-N-PE38 showed enhanced cytotoxicity to HIV-infected, gp120-expressing H9 cells compared to uninfected H9 cells. Competition experiments with free CV-N provided further support that the enhanced FLAG-CV-N-PE38-induced cytotoxicity was due to interactions of the CV-N moiety with cell surface gp120. This study establishes the feasibility of use of CV-N as a gp120-targeting sequence for construction and experimental therapeutic investigations of unique new chimeric toxins designed to selectively destroy HIV-infected host cells.