Gombaspiroketals A–C, Sesterterpenes from the Sponge <i>Clathria gombawuiensis</i>

Gombaspiroketals A–C (<b>1</b>–<b>3</b>), tetracyclic sesterterpenes of a novel skeletal class, were isolated from the Korean marine sponge <i>Clathria gombawuiensis</i>. On the basis of the combined spectroscopic analyses, the structures of these compounds were determined to be highly rearranged sesterterpene spiroketal methoxyacetals (<b>1</b> and <b>2</b>) and a corresponding hemiacetal (<b>3</b>). The relative and absolute configurations were assigned by NOESY analysis and ECD calculations, respectively. These compounds exhibited moderate cytotoxicities and antibacterial activities

Mohangamides A and B, New Dilactone-Tethered Pseudo-Dimeric Peptides Inhibiting <i>Candida albicans</i> Isocitrate Lyase

Mohangamides A and B (<b>1</b>–<b>2</b>) were discovered from a marine <i>Streptomyces</i> sp. collected in an intertidal mud flat. The structures of the compounds were elucidated as novel dilactone-tethered pseudodimeric peptides bearing two unusual acyl chains and 14 amino acid residues based on comprehensive spectroscopic analysis. The absolute configurations of the mohangamides were determined by chemical derivatizations, followed by chromatographic and spectroscopic analyses. Mohangamide A displayed strong inhibitory activity against <i>Candida albicans</i> isocitrate lyase

Cytotoxic Diterpenoid Pseudodimers from the Korean Sponge <i>Phorbas gukhulensis</i>

Four new cytotoxic diterpenoid pseudodimers (<b>2</b>–<b>5</b>), along with a previously reported one, gukulenin A (<b>1</b>), were isolated from the marine sponge <i>Phorbas gukhulensis</i> collected off the coast of Gagu-do, Korea. These novel compounds, designated gukulenins C–F (<b>2</b>–<b>5</b>), were determined by extensive spectroscopic analyses to be pseudodimers of the gagunins, like gukulenin A. The termini of the tropolone-containing side chains in gukulenins C–E (<b>2</b>–<b>4</b>) were found to have diverse modifications involving acetamides or taurine, whereas gukulenin F (<b>5</b>) was formed from <b>1</b> by the ring-opening of a cyclic hemiketal. The relative and absolute configurations were assigned by Murata’s and modified Snatzke’s methods using a HETLOC experiment and a CD measurement of a dimolybdenum complex, respectively. All of these compounds exhibited significant cytotoxicity against the K562 and A549 cell lines

Ohmyungsamycins A and B: Cytotoxic and Antimicrobial Cyclic Peptides Produced by <i>Streptomyces</i> sp. from a Volcanic Island

Ohmyungsamycins A and B (<b>1</b> and <b>2</b>), which are new cyclic peptides, were isolated from a marine bacterial strain belonging to the <i>Streptomyces</i> genus collected from a sand beach on Jeju, a volcanic island in the Republic of Korea. Based on the interpretation of the NMR, UV, and IR spectroscopic and MS data, the planar structures of <b>1</b> and <b>2</b> were elucidated as cyclic depsipeptides bearing unusual amino acid units, including <i>N</i>-methyl-4-methoxytrytophan, β-hydroxyphenylalanine, and <i>N</i>,<i>N</i>-dimethylvaline. The absolute configurations of the α-carbons of the amino acid residues were determined using the advanced Marfey’s method. The configurations of the additional stereogenic centers at the β-carbons of the threonine, <i>N</i>-methylthreonine, and β-hydroxyphenylalanine units were assigned by GITC (2,3,4,6-tetra-<i>O</i>-acetyl-β-d-glucopyranosyl isothiocyanate) derivatization and the modified Mosher’s method. We have developed a new method utilizing PGME (phenylglycine methyl ester) derivatization coupled with chromatographic analysis to determine the absolute configuration of <i>N</i>,<i>N</i>-dimethylvaline. Our first successful establishment of the absolute configuration of <i>N</i>,<i>N</i>-dimethylvaline using PGME will provide a general and convenient analytical method for determining the absolute configurations of amino acids with fully substituted amine groups. Ohmyungsamycins A and B showed significant inhibitory activities against diverse cancer cells as well as antibacterial effects

Manzamine Alkaloids from an <i>Acanthostrongylophora</i> sp. Sponge

Five new manzamine alkaloids (<b>1</b>–<b>5</b>) and new salt forms of two known manzamines (<b>6</b> and <b>7</b>), along with seven known compounds (<b>8</b>–<b>14</b>) of the same structural class, were isolated from an Indonesian <i>Acanthostrongylophora</i> sp. sponge. On the basis of the results of combined spectroscopic analyses, the structure of kepulauamine A (<b>1</b>) was determined to possess an unprecedented pyrrolizine moiety, while others were functional group variants of known manzamines. These compounds exhibited weak cytotoxicity, moderate antibacterial activity, and mild inhibition against the enzyme isocitrate lyase