Hydroquinone derivatives and monoterpenoids from the Neotropical liverwort Plagiochila rutilans

The structure of a prenylbenzene derivative isolated previously from a Cuban specimen of the liverwort Plagiochila rutilans is revised to 2-methoxy-6-prenylhydroquinone. The hydroquinone was observed as a prominent component of the NMR and GC-MS fingerprints of five recent specimens of the liverwort from Bolivia, Brazil and Costa Rica. The corresponding quinone was observed as a minor component. Two new methylated derivatives of the hydroquinone were observed as prominent components in one specimen from Bolivia; these were isolated, characterized, and their structures elucidated as 2-methoxy-1-O-methyl-6-prenylhydroquinone and 2-methoxy-4-O-methyl-6-prenylhydroquinone using 1H NMR spectroscopy. The liverwort has a strong peppermint-like odour that is caused by the presence of several menthane monoterpenoids, including notably pulegone, menthone, isomenthone. terpinolene and limonene. One of the Costa Rican specimens contained considerable amounts of the new lactone 3,7-dimethyl-2,6-octadien-1,6-olide as the principal monoterpenoid in place of pulegone. Two Costa Rican specimens distinguished morphologically as Plagiochila standleyi (a taxon closely related to P. rutilans and reduced elsewhere to a variety of that species) are characterized by large amounts of 3-hydroxy-4'-methoxybibenzyl. P. standleyi was also reported to have a peppermint-like odour in the field. Menthane monoterpenoids were again responsible but in this case the major components were limonene, beta-phellandrene, alpha-terpinene and the endoperoxide ascaridole.