Estudos visando a sÃntese de hÃbridos de tocoferol com Ãcido ascÃrbico

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The antioxidant activity of tocopherol and ascorbic acid, as well as the capacity of the latter to regenerate tocopherol from the tocopheroxyl radical has generated great interest in the synthesis of hybrid molecules containing both of the above moieties in the same molecule. We term such species as potentially autoregenerable radical scavengers. With the intention to develop a synthetic route to such a hybrid molecule, where the phenolic-OH of a-tocopherol and the 2,3-enediol system of ascorbate are free of substitution, model studies have been carried. The aim was to devise a convergent synthesis linking intact units of tocopherol and ascorbate by means of a spacer joining the 5-position of tocopherol to C-6 of ascorbic acid. Starting from 5,6-O-isopropylidene-L-ascorbic acid (11), 2,3-di-O-benzoyl-5,6-Oisopropylidene-L-ascorbic acid (12) was prepared in 78%, with the enediol protected as the dibenzoate. The deprotection of OH-5 and -6 of (12) supplied, in 58%, the 2,3-di-Obenzoyl-L-ascorbic acid (13). Tosylation led to 2,3-di-O-benzoyl-6-O-tosyl-L-ascorbic acid (18). Halogenation of a-tocopherol, using bromine in dry hexane, provided exclusively 5abromo-a-tocopherol (15) in 98% yield. Several studies have been carried out with the purpose of verifying the viability of introducing nucleophiles such as benzylamine and thiophenol into (15) and (18), and thus probe the suitability of these intermediates to act as substitution substrates in a sequential coupling strategy. It was not possible to obtain benzylamine or thiophenyl substitution products in the ascorbate (18). However, the bromotocopherol substrate (15) readily yielded the respective substitution products (28, 86%) and (29, 30%). The preparation of compounds (28) and (29), as well as of the intermediary (18), demonstrates to the possibility of the coupling of the ascorbate and tocopherol units with different spacers containing distinct group. The results show the flexibility of the synthetic route, since it should be possible to use different spacers with different functionalities, allowing the synthesis of some hybrid molecules

ASSUNTO(S)

sÃntese de hÃbridos tocoferol Ãcido ascÃrbico quimica

ACESSO AO ARTIGO

Documentos Relacionados