(-)-Carvone

31336938

(2R,5R)-dihydrocarvone is an industrially applied building block that can be synthesized by site-selective and stereo-selective C=C bond bio-reduction of (R)-carvone. Escherichia coli (E. coli) cells overexpressing an ene reductase from Nostoc sp. PCC7120 (NostocER1) in combination with a cosubstrate regeneration system proved to be very effective biocatalysts for this reaction. However, the industrial applicability of biocatalysts is strongly linked to the catalysts’ activity. Since the cell-internal NADH concentrations are around 20-fold higher than the NADPH concentrations, we produced E. coli cells where the NADPH-preferring NostocER1 was exchanged with three different NADH-accepting NostocER1 mutants. These E. coli whole-cell biocatalysts were used in batch operated stirred-tank reactors on a 0.7 l-scale for the reduction of 300 mM (R)-carvone. 287 mM (2R,5R)-dihydrocarvone were formed within 5 h with a diasteromeric excess of 95.4% and a yield of 95.6%. Thus, the whole-cell biocatalysts were strongly improved by using NADH-accepting enzymes, resulting in an up to 2.1-fold increased initial product formation rate leading to a 1.8-fold increased space-time yield when compared to literature.

(2R,5R)-dihydrocarvone; (R)-carvone; asymmetric reduction; biotransformation; ene reductase; formate dehydrogenase.

Asymmetric Whole-Cell Bio-Reductions of ( R)-Carvone Using Optimized Ene Reductases

Christoph Mahler 1, Christian Burger 1, Franziska Kratzl 1, Dirk Weuster-Botz 1, Kathrin Castiglione 2

2019 Jul 12;

31111291

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.

Catasetum; Chirality; Electrophysiology; Euglossine bees; Eulaema; Perfume-rewarding plants; Pollinators.

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

Katharina Brandt 1, Stefan Dotterl 2, Roman Fuchs 2, Daniela Maria do Amaral Ferraz Navarro 3, Isabel Cristina Sobreira Machado 4, Daniel Dobler 5, Oliver Reiser 5, Manfred Ayasse 1, Paulo Milet-Pinheiro 6

2019 Jun