Malyngamide X: The First (7R)‐Lyngbic Acid that Connects to a New Tripeptide Backbone from the Thai Sea Hare Bursatella leachii

Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties.     

Corchorusides A and B, new flavonol glycosides as α-glucosidase inhibitors from the leaves of Corchorus olitorius

Corchorus olitorius, a highly fibrous vegetable commonly known as moroheiya, has long been recognized for its hypoglycemic activity. Bioassay-guided fractionation of the leaf extract led to the isolation of two new flavonol glycosides named corchorusides A and B, in addition to a major component, capsugenin-25,30-O-β-diglucopyranoside. Corchoruside A comprises a kaempferol moiety connected with caffeic acid, glucose, and a rare methyl glucuronate (MeGlcA). The occurrence of a caffeoyl moiety in corchoruside A enhanced significantly its inhibitory effect toward α-glucosidase compared to that in corchoruside B.     

Chemistry of renieramycins. Part 6: Transformation of renieramycin M into jorumycin and renieramycin J including oxidative degradation products, mimosamycin, renierone, and renierol acetate

The transformation of renieramycin M (1m) into renieramycin J (1j) and jorumycin (2) is presented along with the results of antiproliferative assay data. The chemical stability and the oxidative degradation of 2 and renieramycin E (1e) to generate simple isoquinoline alkaloids, such as mimosamycin (7), renierol acetate (12), and renierone (8) are also described.     

Chemistry of renieramycins. Part 13: Isolation and structure of stabilized renieramycin type derivatives,renieramycins W–Y,from Philippine blue sponge Xestospongia sp., pretreated with potassium cyanide

Three new bistetrahydroisoquinoline marine natural products, renieramycins W (1w), X (1x), and Y (1y), along with two known renieramycins M (1m) and T (1t), were isolated from the pretreated Philippine blue sponge Xestospongia sp. with KCN and their structures were elucidated by comparing their spectral data with those of 1m, 1t, and N-acetylsafracin B (11). Renieramycins W (1w) and X (1x) are the first examples of tiglic acid ester derivatives at the C-1 side chain. Renieramycin Y (1y) possesses a characteristic substitution pattern in A-ring and isolation of it from marine organism strongly evidences to link the possible precursor 3-hydroxy-5-methyl-O-methyltyrosine with both renieramycin and ecteinascidin marine natural products.     

Jorunnamycins A-C, new stabilized renieramycin-type bistetrahydroisoquinolines isolated from the Thai nudibranch Jorunna funebris

Jorunnamycins A-C (1a-c), three stabilized renieramycin-type bistetrahydroisoquinolines, were isolated from the mantles, the visceral organs, and the egg ribbons of the Thai nudibranch Jorunna funebris that was pretreated with potassium cyanide (KCN), along with five known compounds, renieramycins M (2m), N (2n), O (2o), and Q (2q) and mimosamycin (3). The structures of 1a-c were elucidated from spectroscopic data and by chemical conversion of renieramycin M (2m) into 1c via 1a. The chemical stability and the oxidative degradation generating simple isoquinoline alkaloids of a carbinolamine analog 1d, which was easily prepared by reacting 1c with silver nitrate in aqueous acetonitrile, are discussed. The results of cytotoxicity studies are also presented.     

Chemistry of ecteinascidins. Part 2. Preparation of 6'-O-acyl derivatives of stable ecteinascidin and evaluation of cytotoxicity

A large amount of stable ecteinascidin 770 (1b) was isolated from the Thai tunicate, Ecteinascidia thurstoni, which was pretreated with potassium cyanide in buffer solution (pH 7), along with a minor metabolite, ecteinascidin 786 (1c). A number of 6'-O-acyl derivatives 3-19 and three diacetyl derivatives 2a-c of the stable 1b were prepared and evaluated for activity against human tumor cell lines HCT116, QG56, and DU145. Nitrogen-containing heterocyclic ester derivatives such as 12, 13, and 16-19 showed similar in vitro cytotoxicity to 1b, whereas the other derivatives were less cytotoxic than 1b. Furthermore, we discovered that the N-indole-3-carbonyl derivative of ecteinascidin 770 (22) has higher cytotoxicity than 1b.