Preparation and Characterization of Rosmarinecine Derivatives
Keywords:
Rosmarinecine derivatives, hydroxypyrrolizidine, pyrrolizidine, alkaloids, spectroscopyAbstract
Abstract. This work describes the synthesis of 8-tert-butyldimethylsilyloxy- (3), 2,8-bis(tert-butyldimethylsilyloxy)- (4) 2-mesyloxy-8-tert-butyldimethylsilyloxy- (5), and 2-tosyloxyrosmarinecine (6) from selective protection of the different hydroxylgroups of rosmarinecine 2, which was obtained by hydrolysis of rosmarinine 1. The rosmarinine 1 naturally occuring was isolated in good yields (0.66%) from Senecio callosus. The chemoselectivity of the silylation of the hydroxyl groups at position C-2 and C-8 of 2 was controlled by the time of the reaction, which exhibited a higher reactivity for primary hydroxyl than secondary hydroxyl group, as well as the stereochemistry of the group at 1 position, which is trans and cis to the hydroxyl groups at 2 and 7 positions, respectively, where the steric efffect of hydroxyl group at 7 position is evidenced and posible effect of the solvent. The compounds were characterized by 1H, 13C NMR, 1H-1H COSY, HETCOR spectra, infrared and mass spectrometry.
Resumen. Este trabajo describe la síntesis de 8-tert-butildimetilsililoxi- (3), 2,8-bis(tert-butildimetilsililoxi)- (4) 2-mesiloxi-8-tert-butildimetilsililoxi- (5) y 2-tosiloxirosmarinecina (6) a partir de la protección selectiva de los diferentes grupos hidroxilo de la rosmarinecina 2, la cual se obtiene por hidrólisis de la rosmarinina 1. La rosmarinina 1 que se encuentra naturalmente se aisló en buen rendimiento (0.66%) de Senecio callosus. La quimioselectividad de la sililación de los grupos hidroxilo en la posiciones C-2 y C-8 de 2 fue controlada por el tiempo de reacción, el cual mostró mayor reactividad del grupo hidroxilo primario que el secundario, así como la estereoquímica del grupo en la posición 1, el cual se encuentra trans y cis a los grupos hidroxilos en las posiciones 2 y 7, respectivamente, donde el efecto estérico del grupo hidroxilo en la posición 7 es evidenciado y posible efecto del disolvente. Los compuestos fueron caracterizados por espectroscopia de RMN de 1H, 13C, 1H-1H COSY, HETCOR, infrarrojo y espectrometría de masas.
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