Biotransformation of benzaldehyde-type and acetophenone-type derivatives by Pharbitis nil hairy roots.

The glucosylation of some coumarin and flavone derivatives on incubation with the hairy roots of morning glory (Pharbitis nil) was previously reported. We further studied the biotransformation of benzaldehyde- and acetophenone-type derivatives. Vanillin and isovanillin were reduced to alcoholic derivatives and glucosylated at the phenolic and the alcoholic hydroxyl groups. In the case of 3,4-dihydroxybenzaldehyde, the formyl group was reduced and the 3-hydroxyl or 4-hydroxyl groups were glucosylated to give monoglucosides. The 3-hydroxyl group was predominantly glucosylated to the 4-hydroxyl group. 4-beta-D-Glucopyranosyloxy-3-methoxybenzylalcohol was obtained in low yield. In time-course experiments with vanillin, it was found that the high-level reduction of the formyl group and glucosylation of the phenolic hydroxyl group occurred, and finally 4-O-beta-D-glucopyranosylvanillylalcohol was obtained as the main product. In the case of 3,4-dimethoxybenzaldehyde, 3,4,5-trimethoxybenzaldehyde, and salicylaldehyde, the formyl groups were reduced, and then the hydroxyl groups at the benyl position were glucosylated to give alcoholic glucosides in relatively high yields. In 4-hydroxy-3-methoxyacetophenone, the 4-hydroxyl group was glucosylated and two dimerized glucosides, biphenyl and biphenylether types, were obtained in low yields. In acetophenone, 1-beta-D-glucopyranosyloxy-1-phenylethane and 2-beta-D-glucopyranosyloxyacetophenone were obtained. As mentioned above P. nil hairy roots showed various biotransformative activities including glucosylation of phenolic and benzylic hydroxyl groups, reduction of the formyl group near the benzene ring, and phenol oxidation dimerization. The glucosylation reaction was especially interesting for the production of valuable glucosides.

Glucosylation of phenolic compounds by Pharbitis nil hairy roots: I. Glucosylation of coumarin and flavone derivatives.

Hairy roots of medicinal morning glory (Pharbitis nil) showed potent glucosylation activity against umbelliferone and aesculetin, so the glucosylation activity against several phenolic compounds was tested. Some coumarin derivatives and flavone derivatives having phenolic hydroxyl groups were incubated with the hairy roots. The coumarin derivatives and flavone derivatives almost disappeared from the culture medium in half a day. In the case of the coumarin derivatives, a 7-hydroxyl group was easily glucosylated. A methyl group at C-8 somewhat decreased the glucosylation to a hydroxyl group at C-7 of the coumarin skeleton. The 4-hydroxy coumarin derivatives were changed to acetophenone-type glucosides by incubation with the hairy roots through decarboxylation. Several flavonol derivatives were tested for glucosylation by the hairy roots. 3-Hydroxy flavone, 3.6-dihydroxyflavone and 3,7-dihydroxyflavone were glucosylated to give 3-glucosylated derivatives. Of these, 3,6-dihydroxyflavone was highly glucosylated, but not 3-hydroxyflavone or 3,7-dihydroxyflavone to the same degree. In the case of the flavones, a 3-hydroxy group could be predominantly glucosylated, and hydroxyl groups on the A and B ring of the flavones affected glucosylation by the hairy roots.

Umbelliferone released from hairy root cultures of Pharbitis nil treated with copper sulfate and its subsequent glucosylation.

Hairy root cultures of Pharbitis nil treated with CuSO4 and methyl jasmonate (MeJA) produced umbelliferone (1) and scopoletin (2) in the culture medium, and skimmin (3), a beta-D-glucopyranoside of 1, was isolated from the hairy roots. While 1 in the medium increased and reached a maximal level 16 h after the treatment with CuSO4, the amount of 3 in the hairy roots decreased, reaching a minimal level after 8 h, before recovering to a level higher than the basal level after 24 h and then continuously increasing. These observations suggest that 1 was released by the hydrolysis of 3. Umbelliferone (1) inhibited hairy root growth, while skimmin (3) did not. This result suggests that, after the release of 1 as a phytoalexin, the hairy roots glycosylated 1 for the detoxification and re-use of 3 as a source of phytoalexin.