Isolation and structure determination of lyngbyastatin 3, a lyngbyastatin 1 homologue from the marine cyanobacterium Lyngbya majuscula. Determination of the configuration of the 4-amino-2,2-dimethyl-3-oxopentanoic acid unit in majusculamide C, dolastatin 12, lyngbyastatin 1, and lyngbyastatin 3 from cyanobacteria

The structure of lyngbyastatin 3 (1), including the configurations of the two unusual amino acid residues, viz., the 3-amino-2-methylhexanoic acid (Amha) and 4-amino-2,2-dimethyl-3-oxopentanoic acid units (Ibu), has been established by chemical degradation. Analysis of the cyanobacterial samples of lyngbyastatin 3 (1), lyngbyastatin 1 (2), and dolastatin 12 (3) demonstrated that they are mixtures of Ibu epimers [R (major) and S (minor)], whereas the structurally related majusculamide C (4) is a single diastereomer having an S-Ibu unit.     

Cyclic depsipeptides, grassypeptolides D and E and Ibu-epidemethoxylyngbyastatin 3, from a Red Sea Leptolyngbya cyanobacterium

Two new grassypeptolides and a lyngbyastatin analogue, together with the known dolastatin 12, have been isolated from field collections and laboratory cultures of the marine cyanobacterium Leptolyngbya sp. collected from the SS Thistlegorm shipwreck in the Red Sea. The overall stereostructures of grassypeptolides D (1) and E (2) and Ibu-epidemethoxylyngbyastatin 3 (3) were determined by a combination of 1D and 2D NMR experiments, MS analysis, Marfey's methodology, and HPLC-MS. Compounds 1 and 2 contain 2-methyl-3-aminobutyric acid and 2-aminobutyric acid, while biosynthetically distinct 3 contains 3-amino-2-methylhexanoic acid and the β-keto amino acid 4-amino-2,2-dimethyl-3-oxopentanoic acid (Ibu). Grassypeptolides D (1) and E (2) showed significant cytotoxicity to HeLa (IC?? = 335 and 192 nM, respectively) and mouse neuro-2a blastoma cells (IC?? = 599 and 407 nM, respectively), in contrast to Ibu-epidemethoxylyngbyastatin 3 (neuro-2a cells, IC?? > 10 μM) and dolastatin 12 (neuro-2a cells, IC?? > 1 μM).     

Tumonoic acids, novel metabolites from a cyanobacterial assemblage of Lyngbya majuscula and Schizothrix calcicola

Five new metabolites have been isolated from a lyngbyastatin 1- and dolastatin 12-producing assemblage of Lyngbya majuscula and Schizothrix calcicola collected at Tumon Bay, Guam. Structure elucidation employed 2D NMR techniques and chemical derivatization. These compounds have been assigned the trivial names tumonoic acids A (2), B (1), and C (5); methyl tumonoate A (3), and methyl tumonoate B (4). Compounds 1 and 4 were also found in a lyngbyastatin 1-producing strain of L. majuscula from Guam.     

Structural and conformational analysis of hydroxycyclochlorotine and cyclochlorotine, chlorinated cyclic peptides from Penicillium islandicum

A new chlorinated cyclic pentapeptide, hydroxycyclochlorotine (1), has been isolated from Penicillium islandicum, and the structure including absolute stereochemistry of 1 and conformational properties of 1 and cyclochlorotine (2) in DMSO-d6 were elucidated by using extensive 2D NMR and chemical means. Hydroxycyclochlorotine (1) and astin B (3) from Aster tataricus, each containing an allo threonine at residue 2, have a cis proline configuration, whereas cyclochlorotine (2) has two conformational states in solution, which may be produced from cis-trans isomerization of the proline amide bond. The presence of an intramolecular hydrogen bond between Ser (3)-NH and a hydroxyl oxygen atom of alloThr (2) may serve to maintain the backbone conformation with a cis proline amide bond.     

Phytotoxic withanolides from Jaborosa rotacea

Twelve new withanolides were isolated from the aerial part of Jaborosa rotacea: five had a spiranoid delta-lactone (1-5); one contained a 26,12-delta-lactone and a C-12-C-23 bond (6); five corresponded to trechonolide-type withanolides with configuration at C-23 opposite of those previously isolated (7, 8, 10-12); two of these have an additional oxido-bridge between C-21 and C-24; finally a withanolide with a hemiketal ring formed between a 21-hydroxyl and a 12-ketone (13) and the closely related jaborosalactone R were also isolated. New compounds were fully characterized by a combination of spectroscopic methods (1D and 2D NMR and MS). The structures of the spiranoid withanolide and of the epimer of trechonolide A were confirmed by X-ray diffraction studies. Compounds 4, 5, 6, and 8 showed selective phytotoxicity toward monocotyledoneous and dicotyledoneous species.     

Kempopeptins A and B, serine protease inhibitors with different selectivity profiles from a marine cyanobacterium, Lyngbya sp

Two cyclodepsipeptides named kempopeptins A (1) and B (2) were isolated from a collection of a Floridian marine cyanobacterium, Lyngbya sp., that had previously afforded the structurally related potent elastase inhibitors lyngbyastatin 7 and somamide B. The structures of 1 and 2 were elucidated mainly by 1D and 2D NMR spectroscopy, and the absolute configuration was established by chiral HPLC and Marfey's analysis of the degradation products. Kempopeptin A (1) exhibited an IC50 against elastase of 0.32 microM and against chymotrypsin of 2.6 microM, while kempopeptin B (2) inhibited trypsin with an IC50 of 8.4 microM.     

Employing dereplication and gradient 1D NMR methods to rapidly characterize sponge-derived sesterterpenes

The sesterterpene constituents of two Indo-Pacific sponges were investigated and rapidly characterized using aggressive dereplication methods along with gradient 1D NMR techniques. Lendenfeldia frondosa yielded three sesterterpenes: 12beta,16beta,22-trihydroxy-24alpha-methylscalar-25beta,24alpha-olide (1), the 24 epimer of a known compound; 12beta,22-dihydroxy-24-methylscalar-17-en-24,25-olide (2), a known compound; and 22-hydroxy-24-methylsedn-16-en-24-one-12beta,25beta-olide (3), a new compound. A Hyrtios sp. sponge yielded known 12alpha-acetoxy-16beta-hydroxyscalarolbutenolide (5).     

HPLC同时测定布洛伪麻颗粒剂中布洛芬和伪麻黄碱含量

 目的 建立同时测定布洛伪麻颗粒剂中布洛芬和盐酸伪麻黄碱含量的反相HPLC测定法。方法 以双氯芬酸为内标;色谱柱为Shim-pack CLC-DOS柱,流动相为甲醇-磷酸盐缓冲液(含0.05 mol·L^-1磷酸二氢钾和0.01 mol·L^-1磷酸氢二钾)(64∶36),流速为1.0 ml·min^-1,定时程序控制检测波长(0～6 min为215 nm,6～10 min为260 nm);进样量20 μl。结果 布洛芬和盐酸伪麻黄碱分别在0.02～0.40 mg·ml^-1和3.0～60.0 μg·ml^-1范围内线性关系良好,相关系数分别为r=0.9997和r=0.9998。两组分的回收率分别介于98.02%～101.12%和97.71%～101.15%之间,日内和日间 RSD 均低于5%。结论 本法可同时测定布洛伪麻颗粒剂中布洛芬和盐酸伪麻黄碱的含量,而且简便、准确、快速,可用于多批样品的含量测定及质量控制。     

Dovyalicin-type spermidine alkaloids from Dovyalis species

Phytochemical investigations of Dovyalis abyssinica, D. hebecarpa, and D. macrocalyx revealed two new spermidine-type alkaloids, dovyalicin E (3) and dovyalicin F (4), along with the previously described dovyalicin A (1), dovyalicin B (2), and dovyalicin C (5). In addition, a new phenol glucoside, 4-hydroxytremulacin (7), and the new 1,2-cyclohexanediol glucoside 9, as well as the known compounds methyl 1-hydroxy-6-oxocyclohex-2-enecarboxylate (6) and tremulacin (8), were isolated. The structures were established using homo- and heteronuclear two-dimensional NMR experiments and chiroptical methods. At ambient temperature, the N-disubstituted amide 4 exists as a mixture of cis and trans conformers. Variable-temperature (1)H NMR studies showed that time-averaged spectra are obtainable at 348 K, and the activation parameters determined for the rotation about the amide bond were DeltaH++ = 89 +/- 4.6 kJ/mol, DeltaS++ = 65 +/- 14 kJ/mol.K, and DeltaG++(298K) = 70 +/- 4.5 kJ/mol.     

Penasins A-E, long-chain cytotoxic sphingoid bases, from a marine sponge Penares sp

Five sphingoid bases, penasin A (1), penasin B (2), and a mixture of penasins C-E (3-5), were identified from a marine sponge Penares sp. as cytotoxic constituents. The structure of the common polar head part was assigned by analysis of the NMR data, whereas the structures of the long aliphatic chains including the locations of double bond(s) and a branched methyl group were determined by analysis of tandem FABMS and (13)C NMR data together with the GC-MS analysis of ozonolysis products. The absolute configuration of the headgroup was defined for the mixture of 3-5 by the modified Mosher method. Penasins exhibit moderate cytotoxicity against HeLa and P388 cells.     

Cyanopeptolin 954, a chlorine-containing chymotrypsin inhibitor of Microcystis aeruginosa NIVA Cya 43

A new depsipeptide, cyanopeptolin 954 (1), was isolated from the freshwater cyanobacterium Microcystis aeruginosa NIVA Cya 43. The structure of the compound was elucidated by chemical and spectroscopic analyses, including 2D NMR and GC-MS of the hydrolysate. The major structural differences compared to previously characterized heptadepsipeptides of Microcystis are the replacement of the basic amino acid in position 4 by L-leucine, the presence of L-phenylalanine in position 6, and the uncommon residue 3'-chloro-N-Me-L-tyrosine in position 7. Cyanopeptolin 954 inhibited chymotrypsin with an IC50 value of 45 nM. Nostopeptin BN920, formerly isolated from the cyanobacterium Nostoc,(1) was isolated from the same strain of Microcystis, and a cis amide bond between Phe (6) and N-Me-Tyr (7) was shown. Nostopeptin BN920 inhibited chymotrypsin with an IC50 value of 31 nM.     

Plant analysis by butterflies: occurrence of cyclopentenylglycines in Passifloraceae, Flacourtiaceae, and Turneraceae and discovery of the novel nonproteinogenic amino acid 2-(3'-cyclopentenyl)glycine in Rinorea

Following records about feeding habits of nymphalid butterflies, a novel nonproteinogenic L-amino acid, (S)-2-(3'-cyclopentenyl)glycine (11), was discovered in Rinorea ilicifolia, a species where the presence of a cyclopentanoid natural product of this kind was neither known nor anticipated from the taxonomic point of view. Another novel amino acid, (2S,1'S,2'S)-2-(2'-hydroxy-3'-cyclopentenyl)glycine (12), the stereochemistry of which was determined by single-crystal X-ray diffraction, was shown to occur in species belonging to Flacourtiaceae, Passifloraceae, and Turneraceae. These species, many of which serve as hosts for nymphalid butterflies (Acraeinae, Heliconiinae, Argynninae), also produce 2-(2'-cyclopentenyl)glycine. Cyclopentenylglycines are proposed to be novel chemical recognition templates for plant-insect interactions. Ratios between the epimers of (2S)-2-(2'-cyclopentenyl)glycine, which co-occur in plants, were determined by (1)H NMR spectroscopy. Contrary to a previous report, the (2S,1'R) epimer always appears to predominate over the (2S,1'S) epimer. Stereochemical aspects of biosynthesis of natural cyclopentanoid cyanogenic glycosides are discussed in relation to these findings.     

Sesquiterpenoids from antidiabetic Psacalium decompositum block ATP sensitive potassium channels

Ethnopharmacological relevance

The hypoglycemic effect of root and rhizome aqueous decoction of Psacalium decompositum (Asteraceae), a medicinal herb from Mexico, has been experimentally demonstrated, leading to the identification of several hypoglycemic sesquiterpenoids, such as cacalol, and the mixture of 3-hydroxycacalolide, and epi-3-hydroxycacalolide; however, the mechanism of action of these compounds is unknown.

Aim of the study

To establish whether cacalol, cacalone epimer mixture and cacalol acetate may block adenosine triphosphate-sensitive potassium channels (K_ATP channels) in a similar way to the antidiabetic drug glibenclamide.

Materials and methods

Cacalol, cacalone epimer mixture, and cacalol acetate were tested on the diazoxide-induced relaxation of male rat aortic rings precontracted with phenylephrine (3.2 × 10⁻⁶ M).

Results

Cacalol (10⁻⁵ M), cacalol acetate and the cacalone epimer mixture (10⁻⁴ M) inhibited the diazoxide effect, in a similar manner and concentration as glibenclamide (10⁻⁵ M). Cacalone epimer mixture exerted this effect in a concentration-dependent manner (P < 0.01). Cacalol (10⁻⁴ M), irreversibly inhibited the diazoxide-induced relaxation, and displayed activity at a lower concentration (10⁻⁵ M) than cacalone epimer mixture and cacalol acetate.

Conclusions

These results suggest that the studied compounds block K_ATP channels in a similar way to glibenclamide in rat aorta. However, controversial data indicate that Psacalium decompositum sesquiterpenoids are less effective than glibenclamide in lowering plasma glucose levels, suggesting that cacalol and cacalone epimer mixture, as well as cacalol acetate, may display a higher affinity to SUR2 subunit of K_ATP channels in aortic smooth muscle than to SUR1 subunit in pancreatic β-cells.     

Isolation of nor-secofriedelanes from the sedative extracts of Galphimia glauca

Preparative-scale recycling HPLC was used for the complete resolution of a complex mixture of nor-secofriedelanes into five major peaks (I-V) from the sedative methanolic extracts prepared from the aerial parts of Galphimia glauca. Argentation chromatography was used to show peaks I, II, IV, and V to be mixtures of isomers around the E-ring double bond, represented by the endocyclic C-20, C-21 double-bond isomers, galphimines A (3), B (1), D (4), and E (2), and the C-20, C-29 exocyclic forms, galphimines F-I (5-8). Galphimine C (9), isolated from peak III, corresponded to the C-19, C-20 double-bond isomer of the previously known major sedative constituent galphimine B. The characterization of all the new triterpenes (3-9) was performed primarily by high-field NMR spectroscopy. Comparison between experimental and calculated (1)H-(1)H vicinal coupling constants and the analysis of molecular mechanics structures revealed that the ring B of these compounds exists in a boatlike conformation. The absolute configuration for the stereogenic carbinol center at C-4 was established by the application of the Mosher ester derivatization technique carried out in NMR tubes.     

Secoiridoid glycoside and alkaloid constituents of Hydrangea chinensis

A new secoiridoid glycoside, hydrachoside A (1), along with 14 known compounds, was isolated from the leaves of Hydrangea chinensis. The absolute stereochemistry of the side chain attached to C-15 on the secoiridoid glycoside hydrangenoside E (2) was determined by NMR spectral analysis. The structures of compounds 1 and 2 were elucidated on the basis of spectral data. The previously reported structure, hydrachine A (3), was revised as its epimer, (-)-neodichroine (4), a new compound.     

Retinoylserine and retinoylalanine, natural products of the moth Trichoplusia ni

Insect cells convert vitamin A into a number of retinoids that are evolutionarily conserved with those of mammalian cells. However, insect cells also produce additional natural retinoids. Namely, two retinoic acid peptides, N-trans-retinoylserine (1) and N-trans-retinoylalanine (2), have been isolated from a cell line of the common cabbage looper, Trichoplusia ni. These are the first examples of naturally occurring retinoic acid linked to amino acids through an amide bond; the amino acid moieties are depicted in the more common l-configuration, although the absolute configuration was not determined due to the minuscule sample amount.     

Comparative analysis of a neurotoxin from Calliostoma canaliculatum by on-line capillary isotachophoresis/1H NMR and diffusion 1H NMR

NMR spectroscopy has been coupled on-line to capillary isotachophoresis (cITP) to enhance structural analyses of dilute charged species through separation and sample concentration. Microcoils, the most mass-sensitive NMR probes available, provide optimal detection for cITP/NMR. To evaluate the utility of cITP/NMR for natural product analysis, a homogenate of the hypobranchial gland from the marine snail Calliostoma canaliculatum containing a cationic neurotoxin (1, a disulfide-bonded dimer of 6-bromo-2-mercaptotryptamine) was studied. For comparison, hypobranchial gland homogenate was also examined by diffusion-NMR, an alternative approach for NMR mixture analysis. cITP/NMR concentrated the neurotoxin by almost 20-fold and isolated it from some of the other components present in the matrix. However, a minor component, likely a precursor or degradant, co-migrated with compound 1. Diffusion-NMR also did not resolve the two, indicating that the compounds possessed similar diffusion coefficients and electrophoretic mobilities. The strengths and limitations of the two approaches for NMR mixture analysis are discussed.     

Insecticidal cyclodepsipeptides from Beauveria felina

A novel cyclodepsipeptide, iso-isariin B (1), and the known isaridin E (2) were isolated from the entomopathogenic fungus Beauveria felina. Their structures were elucidated using MS/MS fragmentation and extensive 2D-heteronuclear NMR. The X-ray structure of isaridin E was obtained, showing two potent intramolecular H bonds and a type-VI turn with the HyLeu(1)-Pro(2) amide bond in a cis conformation. Iso-isariin B (1) was active against the pest-insect Sitophilus spp. with an LD(50) value of 10 μg/mL. This observation also gives some clues for ecological interpretation of cyclodepsipeptide production by B. felina.     

Tanikolide, a toxic and antifungal lactone from the marine cyanobacterium Lyngbya majuscula.

A new brine-shrimp toxic and antifungal compound, tanikolide 1, has been isolated from the lipid extract of a Madagascan collection of the marine cyanobacterium Lyngbya majuscula. The structure of tanikolide was determined by spectroscopic methods, relying heavily on 2D NMR spectroscopy. The absolute configuration at C-5 of tanikolide was established as R by oxidizing the primary alcohol to an acid and analyzing the corresponding (R)- and (S)-PGME amide derivatives by (1)H NMR.     

BI-32169, a bicyclic 19-peptide with strong glucagon receptor antagonist activity from Streptomyces sp

A new bicyclic 19-peptide, BI-32169, has been isolated from the culture broth of Streptomyces sp. (DSM 14996). Its structure has been established by amino acid analysis, mass spectrometry, and 2D NMR analysis. BI-32169 consists exclusively of protein amino acids and is cyclized from the side chain of Asp(9) to the N-terminus of Gly(1). One disulfide bond between Cys(6) and Cys(19) forms a bicyclic structure. BI-32169 and its methyl ester derivative showed potent inhibitory activity against the human glucagon receptor (IC(50) 440 and 320 nM, respectively) in a functional cell-based assay.