β-Phenyl quenching of 9-phenylphenalenones: a novel photocyclisation reaction with biological implications.

The singlet and triplet excited states of 9-phenylphenalenones undergo β-phenyl quenching (BPQ) via addition of the carbonyl oxygen to the ortho position of the phenyl substituent. This reaction leads to the formation of naphthoxanthenes , which, in the absence of quenchers, undergo a very rapid electrocyclic ring opening reaction reverting to within a few microseconds. Naphthoxanthene contains a remarkably weak C-H bond, which enables efficient hydrogen transfer reactions to suitable acceptors, giving rise to the production of the naphthoxanthenyl radical or the naphthoxanthenium cation, depending on the solvent polarity.

Synthesis and in vitro antiprotozoal evaluation of substituted phenalenone analogues.

A set of derivatives encompassing structural modifications on the privileged phenalenone scaffold were assessed for their antiparasitic activities against the most clinically relevant forms of trypanosomiasis and leishmaniasis. Several compounds exhibited leishmanicidal effects at levels comparable or better than the reference drug pentamidine, while the parent phenalenone was shown to have a level of activity against Trypanosoma cruzi comparable to the marketed drug benznidazole.

Semisynthesis and biological evaluation of abietane-type diterpenes. Revision of the structure of rosmaquinone.

The new aromatic diterpenes 7beta-O-benzylrosmanol (3), 7beta-O-benzyl-11,12-di-O-methylrosmanol (4), and 7alpha-thiophenylcarnosic acid (5) have been obtained by partial synthesis from carnosol (1), an abundant natural diterpene present in Salvia species. The structures of these compounds were established from their physical and spectroscopic data. The known diterpenes sagequinone methide A (6), 7beta-O-methylrosmanol (7), 7-O-methylrosmanol (8), and rosmaquinone B (9) were obtained from rosmanol (2).

Abietane diterpenoids from Salvia pachyphylla and S. clevelandii with cytotoxic activity against human cancer cell lines.

A phytochemical study has been carried out on the aerial parts of Salvia pachyphylla and S. clevelandii. From S.

Quinone derivatives by chemical transformations of 16-hydroxycarnosol from Salvia species.

The known diterpenes 12,16-epoxycarnosol (2), isotanshinone II (6), and (+)-neocryptotanshinone (8) were obtained by partial synthesis from 16-hydroxycarnosol (1), a C-16 hydroxylated abietatriene diterpene isolated in relative abundance from the aerial part of Salvia mellifera GREENE. The physical and spectroscopic data of these semisynthetic diterpenes were identical to those given for the natural ones in the literature. These abietane diterpenes have very interesting biological activities and the semisynthetic approach described here represents an alternative to obtain them from other major diterpenes isolated from Salvia species.

Phototoxic phytoalexins. Processes that compete with the photosensitized production of singlet oxygen by 9-phenylphenalenones.

Experiments were performed to elucidate the excited-state behavior of 9-phenylphenalenones, which are phototoxic plant secondary metabolites involved in mechanisms of light-mediated plant defense. Using a combination of time-resolved and steady-state UV/visible spectroscopies, time-resolved IR absorption spectroscopy, time-resolved singlet oxygen phosphorescence measurements and cyclic voltammetry, we provide evidence of an intramolecular charge-transfer process in the excited singlet and the triplet states of 9-phenylphenalenones that modulates the photosensitized production of singlet oxygen.

Light- and singlet oxygen-mediated antifungal activity of phenylphenalenone phytoalexins.

The light-induced singlet oxygen production and antifungal activity of phenylphenalenone phytoalexins isolated from infected banana plants (Musa acuminata) are reported. Upon absorption of light energy all studied phenylphenalenones sensitise the production of singlet oxygen in polar and non-polar media. Antifungal activity of these compounds towards Fusarium oxysporum is enhanced in the presence of light.

Fungus-elicited metabolites from plants as an enriched source for new leishmanicidal agents: antifungal phenyl-phenalenone phytoalexins from the banana plant (Musa acuminata) target mitochondria of Leishmania donovani promastigotes.

Two antifungal phenyl-phenalenone phytoalexins isolated from the banana plant (Musa acuminata) elicited with the fungus Fusarium oxysporum, together with a methoxy derivative of one of them and two epoxide precursors of their chemical synthesis, were tested for leishmanicidal activity on Leishmania donovani promastigotes and L. infantum amastigotes. Drugs inhibited proliferation of both forms of the parasite with a 50% lethal concentration range between 10.

Rhoiptelenol and rhoiptelenone, two pentacyclic triterpenes from Sideritis macrostachya.

The pentacyclic triterpenes rhoiptelenol and rhoiptelenone have been isolated from Sideritis macrostachya. Rhoiptelenone is a new natural compound, whose structure has been determined as D:B-friedo-urs-5-en-3-one. The 1H and 13C NMR spectra of rhoiptelenol, rhoiptelenol acetate and glutinol have been reassigned.

Semisynthesis of rosmanol and its derivatives. Easy access to abietatriene diterpenes isolated from the genus Salvia with biological activities.

The known diterpenes rosmanol (3), rosmaquinone (4), 7-methoxyrosmanol (5), 7-ethoxyrosmanol (6), galdosol (7), and epirosmanol (8) have been obtained by partial synthesis from carnosol (2), an abundant natural product present in Salvia species. The physical and spectroscopic data of these semisynthetic diterpenes were identical to those of authentic natural samples and with data reported in the literature. These abietane diterpenes have very interesting biological activities and are present in the genus Salviain low quantities; thus, the semisynthetic approach described here represents an efficient alternative method to obtain these compounds.