Subtle Chemical Variations with Strong Ecological Significance: Stereoselective Responses of Male Orchid Bees to Stereoisomers of Carvone Epoxide.

Different enantiomers of chiral compounds within floral perfumes usually trigger distinct responses in insects; however, this has frequently been neglected in studies investigating semiochemicals in plant-pollinator interactions. Approximately 1000 neotropical plants produce floral perfumes as the only reward for pollinators, i.e. male euglossine bees. The chiral compound carvone epoxide is a key component of the scent bouquet of many perfume-rewarding plants that are pollinated by males of Eulaema. Here, we tested the biological activity of the four carvone epoxide stereoisomers to four Eulaema species occurring in the Atlantic Rainforest of NE-Brazil. We determined the stereochemistry of carvone epoxide in the floral scent of several Catasetum species, tested whether the antennae of bees respond differentially to these stereoisomers and investigated if there is a behavioural preference for any of the stereoisomers. We found that 1) Catasetum species emit only the (-)-trans-stereoisomer of carvone epoxide, 2) for E. atleticana and E. niveofasciata antennal responses to the (-)-trans-carvone epoxide were significantly stronger than those to (-)-cis-carvone epoxide, 3) the strength and pattern of antennal responses to all 4 stereoisomers (separately tested) did not differ among Eulaema species, and 4) there were significant differences in attractiveness of the four stereoisomers to the bees species with the (-)-trans-stereoisomer being particularly attractive. We assume (-)-trans-carvone epoxide to be the dominant isomer in perfume-rewarding plants pollinated by Eulaema. The universal occurrence of carvone epoxide in Catasetum species pollinated by Eulaema, suggests that this compound has evolved in perfume-rewarding as a specific attractant for Eulaema bees as pollinators.

Synthesis of 6-Substituted 2-Pyrones Starting from Renewable Resources: Total Synthesis of Sibirinone, (E)-6-(Pent-1-en-1-yl)-2H-pyran-2-one, and (E)-6-(Hept-1-en-1-yl)-2H-pyran-2-one.

An atom-economic reaction sequence to 6-substituted 2-pyrones was developed starting from furfuryl alcohol, a renewable resource made from bran or bagasse, and aldehydes, utilizing a thermal rearrangement of cyclopentadienone epoxides as key step. Derivatives bearing a hydroxyalkyl side chain could be enzymatically resolved, providing access to enantiomerically pure 2-pyrones, or converted to alkenyl-substituted 2-pyrones such as naturally occurring sibirinone, (E)-6-(pent-1-en-1-yl)-2H-pyran-2-one, and (E)-6-(hept-1-en-1-yl)-2H-pyran-2-one.

Hydrogen bond acceptors and additional cationic charges in methylene blue derivatives: photophysics and antimicrobial efficiency.

Photodynamic inactivation of bacteria (PIB) by efficient singlet oxygen photosensitizers might be a beneficial alternative to antibiotics in the struggle against multiresistant bacteria. Phenothiazinium dyes belong to the most prominent classes of such sensitizers due to their intense absorption in the red-light region (λ(abs, max) ca. 600-680 nm, ε > 50,000 L mol(-1) cm(-1)), their low toxicity, and their attachment/penetration abilities. Except simple substituents like alkyl or hydroxyalkyl residues, nearly no modifications of the phenothiaziniums have been pursued at the auxochromic sites. By this, the properties of methylene blue derivatives and their fields of application are limited; it remains unclear if their potential antimicrobial efficacy may be enhanced, also to compete with porphyrins. We prepared a set of six mainly novel methylene blue derivatives with the ability of additional hydrogen bonding and/or additional cationic charges to study the substituents' effect on their activity/toxicity profiles and photophysical properties. Direct detection of singlet oxygen was performed at 1270 nm and the singlet oxygen quantum yields were determined. In suspensions with both, gram-positive and gram-negative bacteria, some derivatives were highly active upon illumination to inactivate S. aureus and E. coli up to 7 log10 steps (99.99999%) without inherent toxicities in the nonirradiated state.