The Geography of Phytochemical Races

242 5 Wide Disjunctions
comparable distances. That situation will be discussed with below, but fi rst we will
look at some other work involving L. obtusa.
Collections of L. obtusa from sites in the eastern Mediterranean Sea, in the Gulf
of Suez, and in the Canary Islands have provided additional insights into chemical
complexity of this taxon. One of the most structurally complex groups of algal
products are the allenes, compounds characterized by the presence of a carbon atom
connected to each of its neighbors by a double bond. Representative of this class of
compounds is structure [497] (see Fig. 5.12 for structures 497–499) isolated from
plants collected at Kas (36°12′N, 29°38′E) in southwestern Turkey (Oztunc et al.,
1991). Plants collected near Hurghada, Egypt, which lies about 40 km south of the
Gulf of Suez, afforded an array of compounds, including several akin to obtusane
[498] (Ayyad et al., 1990), and a new sesquiterpene ether [499] (Ayyad et al., 1994).
Finally, we can cite the work of J. D. Martin et al. (1989) who reported halogenated
compounds built on the obtusane skeleton from collections made near the islands
of Grand Canary and Lazarote in the Canary Islands. Only minor differences in the
profi les of these compounds were observed between those two sites.
Laurencia synderae Dawson was collected from two sites, one near La Jolla (the
type locality) and one near Santa Catalina Island, and examined for their terpenoid
constituents (Howard et al., 1980). The La Jolla material afforded β-synderol [500]
as the major component, whereas the Catalina Island alga gave the bromine-free catabolic
product of β-synerol [501] as the major compound. The formation of the latter
compound can be rationalized as an elimination of halogen followed by rearrangement
of the ring system and subsequent aromatization. Culturing L. synderae (grown
from spores) under various sets of conditions, including temperature, photoperiod,
agitation, or source of seawater, did not alter the plant’s capacity to form β-synderol
as the major product. No trace of the rearranged compound was detected.
In a related study from the same laboratory (Howard et al., 1980), terpenoids
were examined from L. pacifi ca Kylin sampled from four sites, two in the vicinity
of La Jolla (North Bird Rock and Dike Rock) and one each near Carmel (Stillwater
Cove), and Dana Point in Orange County. Plants collected from Dike Rock afforded
a complex mixture from which the four compounds identifi ed as [502–505] were
obtained (see Fig. 5.12 for structures). Plants from Stillwalter Cove had the same
four compounds but they were present in different proportions, whereas material
from Dana Point had only the two bromine-containing compounds. In the case of
all of these collections, material grown in culture gave the same profi les, although
proportions were sometimes different. Those workers concluded that the halogenated
terpene profi les in this species are little affected by external physical factors.
In other words, these common garden-type growth experiments suggest that the
terpene chemistry is under genetic control.
Additional support for this suggestion came from a study of L. distichophylla
J. Agardh collected off the northeastern coast of New Zealand by Blunt et al. (1984).
These workers examined the sesquiterpene chemistry of plants collected at three
depths: (1) low intertidal to upper subtidal; (2) mid-intertidal; and (3) upper intertidal.
Chromatographic fi ngerprints of the latter two collections were identical, but
the profi le of the deep-gathered plants differed in both the number of compounds