RESUMO
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 mirabimideâ E (4) and dysideapyrrolidone (5), and methyl 5-benzyltetramate (2 g) is a substructure in the potent antineoplastic dolastatinâ 15 (3). On the basis of this method, the first asymmetric synthesis of the antimitotic tetrapeptide belamideâ 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 (+)-belamideâ A (7) been confirmed, but also the solvent used for recording the (13) Câ NMR spectrum, the (13) Câ NMR spectrum data correlation, and optical rotation data of natural belamideâ A (7) have been revised.
Assuntos
Produtos Biológicos/química , Produtos Biológicos/síntese química , Toxinas Marinhas/química , Oligopeptídeos/química , Oligopeptídeos/síntese química , Pirrolidinonas/química , Pirrolidinonas/síntese química , Conformação Molecular , Estrutura Molecular , EstereoisomerismoRESUMO
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.
Assuntos
Cinamatos/isolamento & purificação , Ácido Elágico/isolamento & purificação , Quempferóis/isolamento & purificação , Melastomataceae/química , Plantas Medicinais/química , Ácidos Cafeicos/química , Ácidos Cafeicos/isolamento & purificação , Cinamatos/química , Ácido Elágico/química , Flavonoides/química , Flavonoides/isolamento & purificação , Quempferóis/química , Estrutura Molecular , Quercetina/análogos & derivados , Quercetina/química , Quercetina/isolamento & purificação , Resinas SintéticasRESUMO
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.
Assuntos
Produtos Biológicos/síntese química , Imidas/síntese química , Oligopeptídeos/síntese química , Pirróis/síntese química , Benzeno/química , Estrutura Molecular , EstereoisomerismoRESUMO
(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.