The crude extract of the marine brown alga Dictyota guineensis was analyzed by high-resolution gas chromatography-mass spectrometry (HRGC-MS). Five diterpenes were identified: dictyol E (the most abundant diterpene), dictyotadiol, dictyoxide, isopachydictyol A and pachydictyol A, all diterpenes from the chemical group I, i.e., mainly prenylated derivatives of known sesquiterpene skeletons that result from a first cyclization of geranyl-geraniol between positions 1 and 10. These diterpenes are known for their activity against bacteria, fungi and other activities. The results characterize D. guineensis as a species that yields exclusively diterpenes from group I, with low oxidation and low structural complexity. On Brazilian coasts, only D. mertensii provides exclusively prenylated guaiane diterpenes. Although D. guineensis presents alternate branches and fixing by rhizoidal branches, it is easily distinguishable from D. mertensii by the much narrower stem, short stature and flabelliform habit of the former species. On the other hand, both species have been characterized as producers of diterpenes of group I, in particular, prenylated guaiane. However, D. guineensis has a majority dictyol E in the lipophilic extract, while D. mertensii produces more complex prenylated guaianes, like dictyol H.

Os extratos brutos de espécimes da alga parda D. menstrualis, conhecida por produzir diterpenos como principais metabólitos secundários, foram analisados quanto ao modo de armazenamento antes da extração e tipo de solvente utilizado na obtenção do extrato bruto. Os solventes utilizados foram uma mistura diclorometano:metanol (2:1) e acetona. Os espécimes de D. menstrualis foram submetidos a três formas de armazenamento, denominados fresco, seco e congelado. Não foram observadas diferenças qualitativas nas amostras obtidas de quaisquer dos extratos brutos na análise por CG/EM, sendo compostas pelos diterpenos pachydictyol A (I), 6-hidroxi-dichotoma-3,14-dieno-1,17-dial (II), 6-hidroxi-2,7-cicloxenia-3,14-dieno-1,17-dial (III) e 6-acetoxi-dichotoma-3,14-dieno-1,17-dial (IV). Os resultados indicaram que a extração mais eficaz para os componentes de média polaridade de D. menstrualis foi obtida com o uso de acetona, que promoveu extração mais seletiva, mesmo apresentando menor rendimento em massa. Quanto à forma de armazenamento das algas, foi constatado que as metodologias não diferiram significativamente entre si, apesar da tendência de algas congeladas fornecerem o menor rendimento no total de diterpenos. Portanto, nos trabalhos envolvendo análises químicas de extratos brutos de macroalgas marinhas, a escolha do solvente de extração deve ser considerada como fator importante na varredura de substância bioativas.

Crude extracts from specimens of the brown seaweed Dictyota menstrualis, known to produce diterpenes as their major secondary metabolites, were analyzed according to storage procedures before extraction, and the solvent types used to obtain the crude extracts. The specimens of D. menstrualis were submitted to three types of storage procedures, such as wet, dry, and frozen and were extracted with a mixture of dichloromethane:methanol (2:1) and acetone. Qualitative differences were not observed by GC/MS analyses of all crude extracts containing mainly the diterpenes pachydictyol A (I), 6-hydroxy-dichotoma-3,14-diene-1,17-dial (II), 6-hydroxy-2,7-cycloxenia-3,14-diene-1,17-dial (III), and 6-acetoxy-dichotoma-3,14-diene-1,17-dial (IV). The most efficient and selective extraction of the compounds with intermediate polarity produced by D. menstrualis was obtained using acetone, but with less mass production. In general, the storage procedures produced very similar results, but the frozen samples furnished low amount of total diterpenes. According to these results on chemical analysis of crude extracts of seaweeds, the choice of solvent to extraction should be considered as important aspect to better screening bioactive compounds.