Bengazoles C-G from the Sponge Jaspis sp. Synthesis of the Side Chain and Determination of Absolute Configuration

Five new antifungal bengazoles (C-G) were isolated and fully characterized from a marine sponge of the genus Jaspis sp. Bengazoles C-G, together with the known bengazoles A and B, comprise a homologous series of n, iso, and anteiso fatty acid esters (C(13)-C(16)) of the same heterocyclic bis(oxazolyl)methanol parent. The complete relative and absolute configurations of the bengazoles were determined by application of the modified Mosher method and interpretation of exciton coupling in the CD spectra of the tetra-p-bromobenzoate derivatives of bengazole A and that of a model tetrol synthesized in seven steps from L-fucose.     

Lobocyclamides A-C,lipopeptides from a cryptic cyanobacterial mat containing Lyngbya confervoides

The structures of lipopeptides lobocyclamides A (1), B (2), and C (3) were solved using a combination of mass spectrometry, 2D NMR spectroscopy, and degradative analysis. Lobocyclamides B and C are the first peptides reported with the unusual amino acid 4-hydroxythreonine and also incorporate the rare homologous long-chain beta-amino acids 3-aminooctanoic acid and 3-aminodecanoic acid, respectively. The absolute configurations of the amino acid residues in each compound were assigned, after acid hydrolysis, by either direct chiral HPLC comparison with authentic standards or by prior derivatization by Marfey's method and reversed-phase HPLC. Both compounds exhibited moderate antifungal activity against a panel of Candida spp., including two fluconazole-resistant strains. When tested as a mixture, lobocyclamides A and B displayed synergistic in vitro antifungal activity, a phenomenon noted earlier for the related peptides laxaphycins A and B.     

Structure of (-)-neodysidenin from Dysidea herbacea. Implications for biosynthesis of 5,5,5-trichloroleucine peptides

[structure: see text]Neodysidenin was isolated from the marine sponge Dysidea herbacea (Keller 1889) collected on the Great Barrier Reef. The complete configuration was obtained from a combination of methods, including capillary electrophoresis of Marfey's derivatives. Neodysidenin belongs to the L-series of trichloroleucine peptides, and the configuration of the N-methyl thiazolyl alanine residue (13R) is opposite to that of dysidenin.     

Dilithium tetrabromonickelate (II) as a source of soft nucleophilic bromide : Reaction with epoxides

Dilithium tetrabromonickelate (II) in THF serves as a source of “soft” nucleophilic bromide and reacts regioselectively with epoxides to give bromohydrins in high yield.     

Phorbasides A-E, cytotoxic chlorocyclopropane macrolide glycosides from the marine sponge Phorbas sp. CD determination of C-methyl sugar configurations

Five new cytotoxic macrolide glycosides phorbasides A-E (3-7), each possessing a macrolide ring appended to a rare ene-yne-trans-2-chlorocyclopropane, were isolated from the same Western Australian sponge (Phorbas sp.) that provided phorboxazoles A and B. The structures of 3-7 were solved by analysis of spectroscopic data including NMR, MS, and CD. A synthesis of methyl 2-O-methyl-alpha-L-evalose from L-rhamnose was completed and used for configurational assignment of the sugar residue in 3. Acid-catalyzed methanolysis of 3 followed by two-step derivatization of the liberated O-methyl glycoside gave a vicinal 4-O-naphthoyl/tertiary 3-N-(2-aminonaphthyl)carbamate derivative that exhibited exciton coupled CD identical with that of the derivative prepared from synthetic 1,2- O-dimethyl-alpha-L-evalose.     

Progressive-convergent elucidation of stereochemistry in complex polyols. The absolute configuration of (-)-sagittamide A

The absolute stereostructure of sagittamide A (1), a O-hexacetyl long-chain hexahydroxy-alpha,omega-dicarboxylic acid, was assigned using a progressive-convergent approach that integrates three powerful regimens for stereochemical analysis of acyclic natural products: J-based analysis, 13C NMR universal database comparisons, and exciton coupling circular dichroism.     

Amplification of the Cotton Effect of a Single Chromophore through Liposomal Ordering—Stereochemical Assignment of Plakinic Acids I and J

A dramatic effect is observed when acyclic N‐(2‐naphthamides) of medium‐chain 1‐amino‐2‐methylalkanes are partially ordered with the help of liposomes: the Cotton effect arising from π–π* transitions of the terminal naphthamide chromophor is enormously enhanced. This effect was exploited to assign the configuration of new polyketide peroxides such as 1 from the sponge Plakortis halichondroides.

     

Sagittamides A and B. Polyacetoxy long-chain acyl amino acids from a didemnid ascidian

[structure: see text]. An unidentified tunicate from Pohnpei, Micronesia, yielded sagittamides A and B-compounds comprising a long-chain C26 dicarboxylic acid that acylates terminal L-valine and L-ornithine groups. The structures, which contain an unprecedented internal O-hexacetyl-1,2,3,4,5,6-hexaol moiety, were determined by combined spectroscopic analysis including mass spectrometry and 1D and 2D NMR and chemical degradation. The partial absolute stereochemistry of the new compounds was addressed by Marfey's analysis.