Biochemical Systematics and Ecology 29 (2001) 313–316
Chemotaxonomic study of the diterpenes from
the brown alga
Dictyota menstrualis
$
Vale´ria Laneuville Teixeira
a,*, Diana Negra˜o Cavalcanti
b,
Renato Crespo Pereira
aaDepartamento de Biologia Marinha, Universidade Federal Fluminense, C.P. 100.644, 24001-970, Nitero´i, RJ, Brazil
bPrograma de Po´s-Graduac¸a˜o em Quı´mica Orgaˆnica, Instituto de Quı´mica, Universidade Federal Fluminense, 24020-150, Nitero´i, RJ, Brazil
Received 12 November 1999; accepted 1 March 2000
Keywords: Dictyota menstrualis;D. dichotoma; Dictyotales; Phaeophyta; Diterpenes; Chemical ecology
1. Subject and source
In order to continue our chemosystematic studies of the genus Dictyota
Lamouroux, Dictyotales, Phaeophyta (Cavalcanti et al., 1998a and references
quoted therein) we examined D. menstrualis (Hoyt) Schnetter, Ho¨rnig &
Weber-Peukert collected at Enseada do Forno, Bu´zios, Rio de Janeiro State, Brazil (228450S
and 418520 W). Voucher specimens (HB 84815) are deposited in the Herbarium
Bradeanum of the Universidade do Rio de Janeiro, Brazil.
2. Previous study
Diterpenes are the main secondary metabolites present in the genus Dictyota
(Teixeira and Kelecom, 1988; 1989; Teixeira et al., 1990). Previous investigation of
the brown alga D. menstrualis collected at Radio Island, North Carolina, USA,
yielded pachydictyol A, a well-known prenylated guaiane diterpene, dictyol E, and the dialdehyde, dictyodial, a possible precursor of the dichotomane diterpenes
$Part 9 in the series ‘‘Chemotaxonomy of Dictyotales (Phaeophyta)’’ *Corresponding author.
E-mail address:[email protected] (V.L. Teixeira).
(Cronin et al., 1995). (6R)-6-Hydroxydichotoma-3,14-diene-1,17-dial (1) and its
acetate (2) are restricted to AustralianD. dichotoma(Hudson) Lamouroux (Blount
et al., 1982).
3. Present study
The fresh material (1.42 kg) was extracted with CH2Cl2/ MeOH (2 : 1). The
brownish residue (22 g) after concentration was partitioned between n-hexane and
MeOH. Evaporation of the hexane fraction afforded 16 g of residue, rapid separation
of which on silica gel and elution with n-hexane, CH2Cl2, EtOAc, and MeOH,
yielded four fractions. The fraction eluted with CH2Cl2was purified by silica
gel-column chromatography (elution withn-hexane, CHCl3, EtOAc, and MeOH), which
yielded seven fractions. The fraction eluted with n-hexane contained crude
pachydictyol A (250 mg), which was purified by silica gel-column chromatography
(eluent: gradient of CHCl3 in EtOAc) giving pure pachydictyol A (152 mg). The
fraction eluted with CHCl3/EtOAc (9 : 1) gave crude 1 (545 mg). This fraction was
purified by preparative TLC and eluted with EtOAc in CHCl3(1 : 4) giving pure1
(60 mg). Treatment of 1 with acetic anhydride (2 ml) in pyridine (1 ml) gave the
corresponding acetate 2. The presence of 2 as a natural product was observed by
TLC analysis of the crude extract. Compound 2 was isolated and its structure
confirmed by 1H NMR spectroscopy. Diterpenes pachydictyol A, 1 and 2 were
identified by comparison of physical and spectroscopic data with reported values (Hirschfeld et al., 1973; Blount et al., 1982). In this study, we present for the first time
the NMR data of1based on 1D and 2D experiments.1H NMR (300 MHz, CDCl3)
d 9.67 (1H, s, H-1), 9.38 (1H, s, H-17), 7.06 (1H, t, J=3.6 Hz, H-4), 5.09 (1H, tt,
J=7.2 and 1.5 Hz, H-14), 3.58 (1H, s, H-6), 2.42 (2H, d, J= 3.6 Hz, H-5), 2.36 (1H,
d, J=3.3 Hz, H-10), 2.00 (2H, q, J=7.8 Hz, H-13 e H-130), 1.88 (1H, bq, J=7.2 Hz,
H-11), 1.69 (1H, m, H-9), 1.67 (3H, s, H-20), 1.59 (3H, s, H-16), 1.38 (1H, m, H-8),
1.26 (1H, m, H-90), 1.21 (1H, m, H-80), 1.05 (3H, s, 18), 0.45 (3H, d, J=6.6 Hz,
H-19).13C NMR (75.00 MHz, CDCl3)d 203.0 (C-1), 191.7 (C-17), 155.3 (C-4), 140.7
V.L. Teixeira et al. / Biochemical Systematics and Ecology 29 (2001) 313–316
(C-3), 131.0 (C-15), 124.7 (C-14), 73.7 (C-6), 56.4 (C-2), 41.1 (C-5), 38.3 (C-12), 36.2 (C-10), 34.5 (C-7), 33.6 (C-9), 30.6 (C-11), 27.2 (C-18), 25.7 (C-13), 25.6 (C-20), 18.6 (C-8), 17.6 (C-16), 15.9 (C-19).
4. Chemotaxonomic significance
The morphology ofD. menstrualisshowed that this population was very similar to
D. cervicornis Kutzing (collected in Angra dos Reis, RJ, Brazil) (Teixeira et al., 1986a; 1986b; Kelecom and Teixeira, 1988; Fleury et al., 1994). However, TLC
analysis of the extracts ofD. menstrualis(collected at Praia Rasa, Bu´zios, RJ Brazil)
andD. cervicornis(Bu´zios and Angra dos Reis, RJ, Brazil), and the observation of its reproductive structures under an optical microscope, supported the identification of
the collected material as D. menstrualis. The occurrence of Dictyota dichotoma
(Hudson) Lamouroux has been reported in all the oceans based on chemistry (e.g. Blount et al., 1982; Bheemansankara Rao et al., 1986; Kato et al., 1987; Palermo et al., 1994; Dura´n et al., 1997). However, the worldwide distribution of D. dichotoma has been questioned continuously by phycologists who suggest the
division of the D. dichotoma complex into different species (Teixeira et al., 1990;
Schnetter et al., 1987; Ho¨rnig and Schnetter, 1988; Ho¨rnig et al., 1992a; 1992b;
1993). Accordingly, the D. dichotoma populations of the tropical and subtropical
western Atlantic have been taxonomically renamed asDictyota menstrualis (Hoyt)
Schnetter, Ho¨rnig & Weber-Peukert, whileD. dichotomahas been the onlyDictyota
species in the Mediterranean Sea (Schnetter et al., 1987; Ho¨rnig and Schnetter,
1988). The presence of diterpenes1and2inD. menstrualisfrom Brazil suggests that
this species is closely related to the Australian collection ofD. dichotoma. Thus, we
conclude that the studied populations from Brazilian and Australian coasts should
be considered as a single species,D. menstrualis.
5. Ecological significance
In preliminary work, we showed that lipid-soluble extracts of the Brazilian brown algaDictyota menstrualisexhibit feeding-deterrent properties against the amphipod Parhyale hawaiensis(Pereira et al., in press). Bioassay-directed fractionation of this
extract revealed that the deterrent property was due to diterpenoid1 found as the
second most abundant metabolite (about 0.2% - dry mass) ofD. menstrualis(Pereira
et al., in press). This result represents the first evidence of feeding-deterrence of a Dictyotacean metabolite belonging to the dichotomane diterpene skeleton class. Dictyota menstrualis from North America (North Carolina) contains mainly pachydictyol A and natural concentrations of this diterpene inhibit herbivory by fishes and sea-urchin (Hay et al., 1987). Then, our results suggest that the chemical
defense of Dictyota species may vary according to geographic region and may
explain the predominance of a metabolite other than pachydictyol A as the chemical
defense compound ofD. menstrualis from the Brazilian littoral.
Acknowledgements
The authors are grateful to CNPq and FAPERJ for the financial support. D.N.C. gratefully acknowledges CAPES for providing an MSc. fellowship.
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