Acyl tunichlorins: a new class of nickel chlorins isolated from the Caribbean tunicate Trididemnum solidum

A new class of nickel-containing chlorins (acyl tunichlorins) has been isolated from the Caribbean tunicate Trididemnum solidum. The structures of 28 of these nickel (II) hydroporphyrins were elucidated using mass spectrometry, one- and two-dimensional NMR spectroscopy, and chemical degradation/derivatization. Unique structural features of these compounds include the diversity of aliphatic side chains, which are derived from C14:0 to C22:6 fatty acids, and their location at an unprecedented position at C-2a on the hydroporphyrin nucleus. No chlorins with ester-linked acyl side chains at C-2a have been reported previously. Although the exact biological role that these compounds play in T. solidum remains unknown, acyl tunichlorins represent the only nickel-containing chlorins to be isolated from a living system and are the C-2a acyl derivatives of tunichlorin, a nickel chlorin reported by this laboratory in 1988.

Structure--activity relationships of the didemnins

Bioactivities of 42 didemnin congeners, either isolated from the marine tunicates Trididemnun solidum and Aplidium albicans or prepared synthetically and semisynthetically, have been compared. The growth inhibition of various murine and human tumor cells and plaque reduction of HSV-1 and VSV grown on cultured mammalian cells were used to assess cytotoxicity and antiviral activity. Biochemical assays for macromolecular synthesis (protein, DNA, and RNA) and enzyme inhibition (dihydrofolate reductase, thymidylate synthase, DNA polymerase, RNA polymerase, and topoisomerases I and II) were also performed to specify the mechanisms of action of each analogue. Immunosuppressive activity of the didemnins was determined using a mixed lymphocyte reaction (MLR) assay. These assays revealed that the native cyclic depsipeptide core is an essential structural requirement for most of the bioactivites of the didemnins, especially for cytotoxicities and antiviral activities. The linear side-chain portion of the peptide can be altered with a gain, in some cases, of bioactivities. In particular, dehydrodidemnin B, tested against several types of tumor cells and in in vivo studies in mice, as well as didemnin M, tested for the mixed lymphocyte reaction and graft vs host reaction in murine systems, showed remarkable gains in their in vitro and in vivo activities compared to didemnin B.

Biosynthesis of brominated tyrosine metabolites by Aplysina fistularis

The biosynthesis of brominated tyrosine metabolites by the marine sponge Aplysina fistularis was investigated. [U-14C]-L-Tyrosine, [U-14C]-L-3-bromotyrosine, and [U-14C]-L-3,5-dibromotyrosine were incorporated into both dibromoverongiaquinol [1] and aeroplysinin-1 [2], and [methyl-14C]methionine was specifically incorporated into the O-methyl group group of 2. [Methyl-14C]-L-O-methyltyrosine, [methyl-14C]-L-3,5-dibromo-O-methyltyrosine, and several putative nitrile precursors were not incorporated into 1 or 2.

A new polyether acid from a cold water marine sponge, a Phakellia species

A new polyether acid, 14, 15-dihydrodinophysistoxin-1 [1], was isolated along with dinophysistoxin-1 [2] and okadaic acid [3], from an unidentified species of the sponge genus Phakellia. The structure of 1 was assigned by comparison of its 1H- and 13C-nmr and fabms spectral data to those of 2 and 3, as well as interpretation of homonuclear 2D nmr data. Compounds 1-3 showed cytotoxicity against L-1210 leukemia cells with IC50 values of 3 ng/ml. The isolation, structure determination, and biological activities of these compounds are described (1).

Spectomycins, new antibacterial compounds produced by Streptomyces spectabilis: isolation, structures, and biosynthesis

Three new tetrahydroanthracene antibiotics have been isolated from modified culture broths of Streptomyces spectabilis. The new compounds, spectomycins A1, A2 and B1, exist as monomeric (C20H20O7, A1; C19H18O7, A2) and as symmetrical dimeric (C38H34O14; B1) forms. Only spectomycin B1 has moderate activity against Gram-positive microorganisms. We report here the structure elucidation and biosynthetic origin of these compounds.

Berninamycins B, C, and D, minor metabolites from Streptomyces bernensis

Berninamycins B, C, and D were isolated from fermentation of Streptomyces bernensis and their structures were studied with 13C NMR and FAB mass spectrometry. Berninamycin B has a valine unit in its cyclic peptide loop instead of the beta-hydroxyvaline unit found in berninamycin A. Berninamycin D has two fewer dehydroalanine units attached to the carboxyl carbon of the pyridine ring. Based on FAB-MS results, berninamycin C is postulated to have only one dehydroalanine unit attached to the carboxyl carbon of pyridine. The biogenesis of berninamycins B, C, and D is discussed.

Directed biosynthesis of 5"-fluoropactamycin in Streptomyces pactum

A new pactamycin analogue, 5"-fluoropactamycin, was prepared by directed biosynthesis. Supplementation of the fermentation medium of Streptomyces pactum, var. pactum with 3-amino-5-fluorobenzoic acid, an analogue of 3-aminobenzoic acid, an advanced precursor in pactamycin biosynthesis, resulted in co-production of pactamycin and the new pactamycin analogue. A similar feeding experiment with 3-amino-5-methylbenzoic acid did not result in formation of the corresponding methylated pactamycin analogue, but only in inhibition of pactamycin production. Comparison of antimicrobial and cytotoxic activities of pactamycin and 5"-fluoropactamycin showed no significant differences.

Isolation and identification of 12 microcystins from four strains and two bloom samples of Microcystis spp.: structure of a new hepatotoxin

Sixteen microcystins, cyclic heptapeptide hepatotoxins, were isolated and purified by high performance liquid chromatography (HPLC) and thin layer chromatography (TLC) from four hepatotoxic strains and two Microcystis spp. bloom samples originating from five different lakes in Finland. The structures of a new [Dha7]MCYST-FR and 11 known microcystins MCYST-LR, [D-Asp3]MCYST-LR, [Dha7]MCYST-LR, [D-Asp3, Dha7] MCYST-LR, MCYST-RR, [D-Asp3]MCYST-RR, [Dha7]MCYST-RR, [D-Asp3,Dha7]MCYST-RR, [L-Ser7]MCYST-RR, MCYST-YR and [Dha7] MCYST-YR were assigned based on amino acid analysis, fast atom bombardment mass spectrometry (FABMS) and tandem FABMS. Four other new compounds allowed only determination of their molecular formulas and amino acid components because of inadequate amounts obtained. [Dha7]MCYST-RR was found most frequently in these samples as the main toxin.

On the structures of crambescins B and C1

Revised structures have been assigned to the cyclic guanidine-containing crambescins B [3] and C1 [5], from the Mediterranean sponge Crambe crambe. The revisions were based on the fabms/cid/ms spectra of the [M+H]+ ions from crambescins B and C1 and hrfabms measurements on key fragment ions in the ms/ms spectra, which identify losses of C9H19 and C8H18N3O side-chains.

Chemical study of the hepatotoxins from Microcystis aeruginosa collected in California

Four cyclic peptide toxins were purified and quantified from the aqueous extract of algal cell material utilizing high performance liquid chromatography, thin layer chromatography, and fast atom bombardment mass spectrometry. The cyclic peptide toxins appear to be similar structurally to hepatotoxins from previously identified blooms of the blue-green alga Microcystis aeruginosa.

Isolation and identification of eight microcystins from thirteen Oscillatoria agardhii strains and structure of a new microcystin

Microcystins (cyclic heptapeptide hepatotoxins), isolated from 13 freshwater Oscillatoria agardhii strains from eight different Finnish lakes by high-performance liquid chromatography, were characterized by amino acid analysis, fast atom bombardment mass spectrometry (FABMS), and tandem FABMS (FABMS/collisionary-induced dissociation/MS). All strains produced two to five different microcystins. In total, eight different compounds, of which five were known microcystins, were isolated. The known compounds identified were [D-Asp3]MCYST (microcystin)-LR, [Dha7]MCYST-LR, [D-Asp3]MCYST-RR, [Dha7]MCYST-RR, and [D-Asp3,Dha7]MCYST-RR. This is the first time that isolation of these toxins from Oscillatoria spp., with the exception of [D-Asp3]MCYST-RR, has been reported. Three of the strains produced a new microcystin, and the structure was assigned as [D-Asp3,Mser7]MCYST-RR. The structures of two new microcystins, produced as minor components by one Oscillatoria strain, could not be determined because of the small amounts isolated from the cells. Four strains produced [Dha7]MCYST-RR as the main toxin, but [D-Asp3]MCYST-RR was clearly the most abundant and most frequently occurring toxin among these isolates of O. agardhii.

Structural modifications imparting reduced toxicity in microcystins from Microcystis spp

A cyanobacterial (blue-green algal) bloom containing Microcystis aeruginosa (dominant), M. viridis, and M. wesenbergii, was collected from Homer Lake (Illinois, U.S.A.) in the summer of 1988 and microcystins were isolated. One microcystin of substantially reduced toxicity was isolated, together with ten hepatotoxic microcystins. The compound with reduced toxicity was nonlethal at 1 mg/kg (i.p. mouse) and was determined to have a (C3H7O2) mono-ester of the alpha-carboxyl on the Glu unit of microcystin-LR. The other nine microcystins apart from MCLR had approximate LD50S ranging from 97 micrograms/kg to 750 micrograms/kg.

Molecular and crystal structures of ecteinascidins: potent antitumor compounds from the Caribbean tunicate Ecteinascidia turbinata

Some members of marine alkaloid ecteinascidins (Et's), isolated from the Caribbean tunicate Ecteinascidia turbinata, exhibit potent anticancer activity. The three dimensional structures of the N12-formyl derivative of Et729 1a and the natural N12-oxide of Et743 2 have been determined by x-ray crystallography at 0.9 A resolution. Compounds 1a and 2 crystallize in the space groups P2(1)2(1)2(1) (a = 23.214(9) A, b = 28.541(10) A and c = 13.303(9) A) and P2(1) (a = 11.720(5) A, b = 13.230(4) A, c = 28.557(5) A, beta = 90.22(2) degrees), respectively. Their crystal structures have been solved by the Patterson search method, which located the sulfur atoms permitting the phase extension. The final crystallographic R-factors are 0.059 and 0.069 for 1a and 2, respectively. There are two independent molecules, associated as a dimer, in the asymmetric unit of crystals of both 1a and 2. The structure determination allows an unequivocal assignment of the relative configuration of all the chiral centers. Assuming that ecteinascidins and safracin C (whose absolute configuration is known) have the same absolute configuration at C1 position, then the absolute configurations of various chiral positions in Ets are C1(R), N2(R), C3(R), C4(R), C11(R), C13(S), C21(S) and C22(R), respectively. The four independent Et molecules adopt two conformations in which the position of ring C relative to rings A & B is different. The molecules have a compact shape and they are conformationally strained due to a severe van der Waals clash between the sulfur atom and the aromatic ring A. By analogy to the related saframycin, the potent biological activity of Et's may be associated with their ability to form a covalent adduct to DNA using the reactive carbinolamine group. The covalent binding interaction between the Et and the N2 of guanine in the minor groove of the DNA double helix has been studied by computer modelling which suggests that rings A and B "stack" against the DNA backbone. While the bulky drug molecule makes numerous contacts with DNA, it does not significantly distort the conformation of the DNA double helix.

Isolation of <Glu-Asn-Phe-His-Leu-Arg-Pro-NH2 (Antho-RPamide II), a novel, biologically active neuropeptide from sea anemones

Using a radioimmunoassay against the C-terminal sequence Arg-Pro-NH2 (RPamide) we have isolated the neuropeptide <Glu-Asn-Phe-His-Leu-Arg-Pro-NH2 (Antho-RPamide II) from extracts of the sea anemone Anthopleura elegantissima. Addition of low concentrations of Antho-RPamide II to a tentacle preparation of sea anemones inhibited the spontaneous, rhythmic contractions, suggesting that the peptide is a neurotransmitter or neuromodulator.

Chemical characterization and toxicity of dihydro derivatives of nodularin and microcystin-LR, potent cyanobacterial cyclic peptide hepatotoxins

Dihydro derivatives of nodularin (1) and microcystin-LR (4), potent cyclic peptide hepatotoxins isolated from Nodularia spumigena and Microcystis aeruginosa, respectively, were prepared by sodium borohydride reduction of the dehydroamino acid residues. The two stereoisomers of both dihydronodularin (2 and 3) and dihydromicrocystin-LR (5 and 6), isolated by reversed-phase HPLC, showed similar toxicity to each other [ip in mice, LD50 = 150 (2), 150 (3), 85 (5), and 100 (6) micrograms/kg]. The stereochemistries of the reduced amino acids obtained by acid hydrolysis of dihydronodularin and dihydromicrocystin-LR [respectively, alpha-(methylamino)butyric acid and N-methylalanine] were determined by GC on a permethylated beta-cyclodextrin capillary column as their trifluoroacetyl methyl ester derivatives. Authentic L- and DL-N-methylamino acids were prepared to compare directly with the natural amino acids. Deuterated derivatives were also prepared using sodium borodeuteride (98 atom % D), and the location (beta) and percentage (78-84%) of the deuterium incorporation were determined.

A tryptophan-substituted member of the AKH/RPCH family isolated from a stick insect corpus cardiacum

A neuropeptide, Cam-HrTH-I, has been isolated from the corpus cardiacum of the Indian stick insect Carausius morosus. The peptide causes hyperlipaemia in Locusta migratoria and hypertrehalosaemia in Periplaneta americana and is related to the previously isolated Cam-HrTH-II (pGlu-Leu-Thr-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2) by substitution, apparently by a hexose, on the Trp residue. This appears to be the first example of such substitution on a Trp residue.

Additional antitumor ecteinascidins from a Caribbean tunicate: crystal structures and activities in vivo

Ecteinascidins (Ets), isolated from the Caribbean tunicate Ecteinascidia turbinata, protect mice in vivo against P388 lymphoma, B16 melanoma, M5076 ovarian sarcoma, Lewis lung carcinoma, and the LX-1 human lung and MX-1 human mammary carcinoma xenografts. Crystal structures of two tris(tetrahydroisoquinoline) Ets were investigated with single crystals of the 21-O-methyl-N12-formyl derivative of Et 729 and the natural N12-oxide of Et 743. Representatives of an additional class of Ets, Et 722 and Et 736, isolated from the same organism, were assigned tetrahydro-beta-carboline-substituted bis(tetrahydroisoquinoline) structures by NMR and fast atom bombardment MS spectra.

Isolation and structures of microcystins from a cyanobacterial water bloom (Finland)

A hepatotoxic cyanobacterial (blue-green algal) water bloom was collected from a constructed water reservoir in Finland. The water bloom contained two cyanobacterial species, Microcystis aeruginosa and Aphanizomenon flos-aquae. Two hepatotoxins, 1 and 2, were isolated from extracts of lyophilized cells. The structures of 1 and 2 were assigned based upon their amino acid analyses on a Waters Pico Tag HPLC system and a chiral GC capillary column (Chirasil Val III), fast atom bombardment mass spectrometry (FABMS), high resolution FABMS, and tandem FABMS data. Toxin 1 was identical to a previously reported compound, [D-Asp3]microcystin-RR. Toxin 2 was new and was assigned the structure [D-Asp3]microcystin-YR.

Two new L-serine variants of microcystins-LR and -RR from Anabaena sp. strains 202 A1 and 202 A2

Two new microcystins, [L-Ser7]microcystin-LR (1) and [L-Ser7]microcystin-RR (2), were isolated from a filamentous fresh water cyanobacterium (blue-green alga), Anabaena sp. strain 202 A1, along with the two major toxins, [Dha7]microcystin-LR (3) and [Dha7]microcystin-RR (4) and their minor components the D-Asp variants [D-Asp3,Dha7]microcystin-LR (5) and [D-Asp3,Dha7]microcystin-RR (6). Anabaena sp. strain 202 A1 also produced another new toxin, whose structure is tentatively proposed as [D-Asp3,L-Ser7]microcystin-XR (7), where X is a leucine homologue. Anabaena sp. strain 202 A2 produced one new microcystin, 1, and three known microcystins, 3, 4, and 5. The structures of the toxins were assigned based on their amino acid analyses, and fast atom bombardment mass spectrometry data.

Two methyl ester derivatives of microcystins, cyclic heptapeptide hepatotoxins, isolated from Anabaena flos-aquae strain CYA 83/1

Cultured cells of Anabaena flos-aquae strain CYA 83/1, isolated from Lake Edlandsvatn, Norway, produced two microcystin mono-methyl ester derivatives (1 and 2) at the D-Glu unit in addition to microcystin-LR (3), [D-Asp3]microcystin-LR (4), microcystin-RR (5), and [D-Asp3]microcystin-RR (6). Structures of these compounds were assigned based on their amino acid analysis with a Waters Pico Tag HPLC system plus fast atom bombardment mass spectrometry (FABMS), including tandem FABMS, analysis on the two new microcystins, [D-Glu(OCH3)6]microcystin-LR (1) and [D-Asp3, D-Glu(OCH3)6]microcystin-LR (2). Toxicity data were not obtained for 1 and 2 because of the small amounts isolated from the cells.

Isolation and structures of five microcystins from a Russian Microcystis aeruginosa strain CALU 972

Five microcystins were obtained from Microcystis aeruginosa strain CALU 972 isolated from a hepatotoxic water bloom collected in Lake Kroshnosero (Russia). The structure of a new toxin (1) was determined as [Dha7]microcystin-YR by amino acid analyses and fast atom bombardment mass spectrometry, and the toxins 2, 3, 4, and 5 were assigned the structures as [Dha7]microcystin-LR, [D-Asp3,Dha7]microcystin-LR, [Dha7]microcystin-RR, and [D-Asp3,Dha7]microcystin-RR, respectively, by direct comparison with authentic samples.

Structure determination and toxicity of a new microcystin from Microcystis aeruginosa strain 205

A new hepatotoxic microcystin was isolated from the cyanobacterium Microcystis aeruginosa strain 205. Its structure was found to be [Dha7]microcystin-RR as determined by amino acid analysis, mass spectrometry and 1H NMR spectroscopy. LD50 value (i.p. mouse) of this toxin was 180 micrograms/kg. The 48 hr lethal concentration (48-hr-LC50) of the toxin for larvae of the yellow fever mosquito, Aedes aegypti, was 14.9 micrograms/ml.