As configurações dos carbonos C-24 nos compostos (22E)-24-etil-24-metilcolesta-5,22-dien-3b-ol (1) e 24-etil-24-metilcolest-5-en-3b-ol (2), isolados da esponja do caribe colombiano Topsentia ophiraphidites foram determinadas como R e S, respectivamente, com base na comparação dos seus dados de RMN com aqueles de amostras de configurações já definidas 24R e 24S, as quais foram sintetizadas em rotas envolvendo ortoésteres provenientes do rearranjo de Claisen de álcoois D
23-22 alílicos. Este é primeiro estudo de síntese, em que o rearranjo de Claisen é utilizado para introduzir um centro quaternário em C-24, de maneira estereoespecífica e com rendimento aceitável. Análises por difração de raio X de 1 confirmaram essas atribuições estereoquímicas.The C-24 configurations of (22E)-24-ethyl-24-methylcholesta-5,22-dien-3b-ol (1) and 24-ethyl-24-methylcholest-5-en-3b-ol (2), isolated from the Colombian Caribbean sponge Topsentia ophiraphidites, were determined to be R and S, respectively, by comparing their NMR data with those of stereodefined (24R)-and (24S)-samples that were synthesized in routes involving the orthoester Claisen rearrangement of D 23 -22-allylic alcohols. This is the first synthetic study where the Claisen rearrangement is used to introduce a C-24 quaternary center in a stereospecific manner with acceptable yield. X-ray analysis of 1 confirmed these stereochemical assignments.
Steroids U 0300 C-24 Stereochemistry of Marine Sterols: (22E)-24-(Isopropenyl)-22-dehydrocholesterol and 24-Isopropenylcholesterol. -The stereodefined synthesis of dehydrocholesterol derivatives (I) is performed in order to establish the configuration at C-24 of a product which has recently been isolated from the Colombian Caribbean sponge Topsentia ophiraphidites. This naturally occurring product is shown to be (Ia). The related compounds (II) are also prepared. Neither (IIa) nor (IIb) is detected in the sterol mixture obtained from T. ophiraphidites. -(ECHIGO, S.; HARA, N.; CARDERON, G. J.; DUQUE, C.; FUJIMOTO*, Y.; Chem.
The C-24 configuration of (22E,24x x)-24-isopropenyl-22-dehydrocholesterol (1), which was recently isolated from the Colombian Caribbean sponge, Topsentia ophiraphidites, was investigated. The C-24 configuration of 1 isolated from Topsentia ophiraphidites was established to be R in the present study.
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