A flexible asymmetric approach to methyl 5-alkyltetramates and its application in the synthesis of cytotoxic marine natural product belamide†A.

By using a methyl tetramate derivative (R)- or (S)-9 as a novel chiral building block, a direct, flexible, and highly enantioselective approach to methyl (R)- or (S)-5-alkyltetramates (2) is disclosed. Among the synthesized methyl 5-alkyltetramates 2, methyl 5-methyltetramate (2 a) is found in cytotoxic mirabimide E (4) and dysideapyrrolidone (5), and methyl 5-benzyltetramate (2 g) is a substructure in the potent antineoplastic dolastatin 15 (3). On the basis of this method, the first asymmetric synthesis of the antimitotic tetrapeptide belamide A (7) has been achieved in seven steps from (S)-9, with an overall yield of 23.8 %. Not only have the structure and absolute configuration of (+)-belamide A (7) been confirmed, but also the solvent used for recording the (13) C NMR spectrum, the (13) C NMR spectrum data correlation, and optical rotation data of natural belamide A (7) have been revised.

[Study on the chemical constituents from Sarcopyramis nepalensis].

OBJECTIVE: To study the chemical constituents from Sarcopyramis nepalensis. METHODS: Compounds were isolated by D101 macroporous adsorption resin column and purified by repeatedly chromatographic techniques on Sephadex LH-20, silica gel and ODS columnl chromatograph. Their structures were elucidated by chemical and spectral methods. RESULTS: Six compounds were isolated from Sarcopyramis nepalensis, and identified as kaempferol (1), myricetic (2), dihydroquercetin (3), egllagic acid (4), isoferulic acid (5) and caffeic acid (6). CONCLUSION: All compounds are isolated from the genus for the first time.

The first enantioselective synthesis of cytotoxic marine natural product palau'imide and assignment of its C-20 stereochemistry.

Methyl tetramate derivative 6 has been developed as a new building block for the flexible and racemization-free synthesis of methyl 5-benzyl-3-methyltetramate via alkylation, and used in the first asymmetric synthesis of palau'imide (1). This allowed the establishment of the hitherto unknown stereochemistry at the C-20 of palau'imide as S.

A concise asymmetric synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl Acetate and propionate, the sex pheromones of pine sawflies.

(2S,3S,7S)-3,7-Dimethylpentadecan-2-yl acetate (2) and its propionate analogue (3) are the main sex pheromones of all Neodiprion species and Diprion similes, respectively. Starting from (S)-malic acid and employing a highly chemo-, regio-, and stereoselective tandem ester reduction-epoxide formation-reductive epoxide-opening reaction protocol, an efficient total synthesis of (2S,3S,7S)-2 and -3 is reported herein.