| Abstract | dc.description.abstract | Bisbenzylisoquinoline alkaloid-producing cell cultures of Berberis stolonifera were fed with 14C-Iabelled
tyrosine, tyramine, and several chiral l-benzyl-l,2,3,4-tetrahydroisoquinolines. Berbamunine subsequently isolated
from these cuItures showed significan tiy higher incorporation than 2-norberbamunine, berbamine, aromoline or
isotetrandrine, suggesting that it is the first dimer formed in these cells. L-Tyrosine labelled the isoquinoline and
benzyl moieties of berbamunine is ea equal ratios (1.2: 1). Tyramine was almost exclusively incorporated into the
isoquinoline portion of this dimer. (R)-N-Methylcoclaurine gave the highest relative incorporations into bisbenzylisoquinolines
(29% into berbamunine), followed by (R)-coclaurine (10%), (S)-coclaurine (5.2%), and (S)-Nmethylcoclaurine
(2.4%). As both (S)-coclaurine and (S)-N-methylcoclaurine are well incorporated into the protoberberine
fraction (21 and 54%, respectively), these results indicate that the dimerization pathway and the C-3'hydroxylation
leading to reticuline are competing for these substrates. Feeding experiments with (1-13C)-(R)- and (S)coclaurine
and NMR studies of the resulting alkaloids confirmed the biosynthetic route to berbamunine, and also
showed that the (R) isomer is incorporated in similar isotopic excess into both halves of the (R, R) dimer
guattegaumerine which had not been found previously in Berberis species. No racemization of (S)- to (R)-coclaurine
(or its derivatives) or vice versa occurs in this tissue. | es_CL |
