The Geography of Phytochemical Races

4.5 Western Pacifi c: Eastern Asia, Japan, and the Philippines 213
Fig. 4.18 Compounds 377–383, phenylpropanoids derivatives from Heterotropa
name, the distribution of the compounds of note provided an interesting view of
colonization of the Japanese islands. The compounds are arranged in Fig. 4.18 to
indicate their biosynthetic relationships and follow the presentation of Hayashi et al.
(1984). The upper sequence of reactions, eugenol [377] to safrole [378] to myristicin
[379] to apiole [380], involves fi rst the formation of the methylenedioxy function,
which requires oxidation of the O-methyl group in eugenol followed by cyclization.
Formation of the methylenedioxy system does not occur in the lower-reaction
sequence, where the pathway proceeds from eugenol to methyleugenol [381] to
elemicin [382] to 1-allyl-2,3,4,5-tetramethoxybenzene [383]. Subsequent events in
each pathway involve ring oxidation and O-methylation, in each case leading to the
same level of oxidation, four substituted phenolic groups in each terminal product.
Mapping the distribution of these compounds reveals an interesting difference in
the profi les of the terminal products of the two pathways. Apiole, which contains the
methylenedioxy ring system, was observed only in species collected from Okinawa,
the Yaeyama Islands, and Taiwan. The terminal compound in the nonmethylenedioxy
pathway, 1-allyl-2,3,4,5-tetramethoxybenzene, was observed primarily in
species form Central Honshu but with a high concentration in “H. costata” from
western Honshu and the island of Shioku (see Fig. 4.19). These observations were
rationalized in terms of two routes of migration from the Chinese mainland: species
with the methylenedioxy-based compounds migrated via a southern route; species
with the nonmethylenedioxy-based compounds migrated via a northern route.
Those authors stated that, “It is well known that Heterotropa species are originated
from Yunnan or Szechwan Province in China.” It would have added immeasurably
to the work had the authors included information on the phenylpropene chemistry
of species from those areas. They noted, however, that species of North American
Hexastylis (also included in Asarum according to Mabberley) contains methyl eugenol,
safrole, some terpenes, and elemicin (Hayashi et al., 1983).