Chemoenzymatic routes to rose oxide

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The scent of the rose is one of the most sought after in the fragrance industry and for more general domestic as well as personal products. Eau de toilette contains the lighter, more volatile rose essential oil components such as citronellol and geraniol. Perfumes are longer lasting as they contain less volatile components such as the rose ketones damascone, damascenone, ionones and the like. Another component of rose essential oil is the small molecule rose oxide. Although present in tiny amounts in rose oil, it has an odour threshold of 0.5 parts-per-billion and contributes more to the rose note than all other compounds except for damascone. Rose oxide is described as having a floral, green note and so important that a stamp with its molecular structure printed on it was issued when the compound was first isolated from the oil of Bulgarian roses. Rose oxide is a high value fine chemical because it takes 3 tonnes of rose blossoms to generate 1 kg of rose oil which contains <0.1% rose oxide. Material isolated from natural sources is expensive ($7,000 per kg). Commercially, rose oxide is produced by chemical routes from citronellol; one route uses bromine while others require reagents that are polluting to produce and use. The aim of this project is to develop a biological process to rose oxide from citronellol, with the key step being the oxidation of a specific carbon-hydrogen bond in citronellol. These bonds are chemically inert, which leads to more complex routes or more polluting processes in order to use citronellol as feedstock. We have developed enzyme variants capable of carrying out this critical step in water at ambient temperature. The industry partner for the project is in the process of taking this to commercial scale rose oxide production by a sustainable and non-polluting biotechnological process. The purpose of this project is to develop more active enzymes and alternative feedstocks based on citronellol in order to make the rose oxide process even more efficient and productive. Advanced computational methods will also be applied to help guide enzyme design and process development.