# Natural Compounds in the Battle against Microorganisms--Linalool
## 4 Microbial Biotransformation of Linalool  
Antibiotics are commonly used in the treatment of various infections and, when enter surface waters and soil, negatively affect the local ecosystems. For this reason, it is important to identify the possible degradation pathways for any new antimicrobial drug, including linalool. The first stage of degradation is often biotransformation processes, which are discussed in detail in this section. One of the main reactions that linalool undergoes under the influence of many microorganisms is epoxidation of the double bond followed by cyclization to obtain cyclic ethers. In the case of the (3_R_)-(-)-isomer of linalool, the products can be _trans_-(2\(R\),5_R_)-furanoid linalool oxide, _cis_-(2\(R\),5_5_)-furanoid linalool oxide, and _trans_-(2\(R\),5_5_)-pyranolol linalool oxide and _cis_-(2\(R\),5_R_)-pyranolol linalol oxide. On the other hand, as a result of cyclization of the (3_S_)-(+)-isomer of linalool, the products may be _trans_-(2\(S\),5_S_)-furanoid linalool oxide, _cis_-(2\(S\),5_S_)-furanoid linalool oxide, _trans_-(2\(S\),5_R_)-pyranolol linalool oxide and _cis_-(2\(S\),5_S_)-pyranoid linalool oxide [76]. Both racemic (\(\pm\))-linalool and (3_R_)-(--)-linalool were used as substrate for biotransformation by _Aspergillus niger_ ATCC 9142. Biotransformation was carried out for 20 days. At the time of inoculation, 50 \(\upmu\)L of linalool was added to 100 mL of the medium; after 14 days, another 100 \(\upmu\)L of linalool was added; and after 20 days, the transformation process was completed. In both cases, epoxidation of the double bond took place, followed by cyclization of the resulting epoxide. In the case of (\(\pm\))-linalool, a mixture of _cis_-(2\(S\),5_R_)- and _trans_-(2\(R\),5_R_)-furanoid linalool oxide (15-24% yield), and a mixture of _cis_-(2\(S\),5_S_)- and _trans_-(2\(R\),5_S_)-pyranoid linalool oxide (5-9% yield) resulted. In turn, (3_R_)-(--)-linalool was transformed mainly into _trans_-(2\(R\),5_R_)-furanoid linalool oxide with ee > 95% and _trans_-(2\(R\),5_S_)-pyranoid linalool oxide [77]. Another strain: _A. niger_ DSM 821 was used to biotransformation (3_S_)-(+)-linalool with 77% purity. The main products were _cis_-(2\(S\),5_R_)-furanoid linalool oxide with a yield of 30% and an enantiomeric excess of 100%, and _cis_-(2\(S\),5_S_)-pyranoid linalool oxide obtained with a yield of 14%. Moreover, it was found that the (3_S_)-(+)-isomer of linalool was transformed much better than the (3_R_)-(--)-isomer of linalool, which did not exceed 4% conversion [78]. The same cyclic products were formed during the biotransformation of (3_R_)-(--)-linalool by the _Diplodia gossypina_ ATCC 10936 fungal strain. In this case, 10 \(\upmu\)L of linalool was added to 100 mL of the grown culture and the transformation process was carried out for 24 h. As a result, _trans_-(2\(R\),5_S_)-furanoid linalool oxide with an efficiency of 12% and ee = 97% and _trans_-(2\(R\),5_R_)-pyranoid linalool oxide with an efficiency of 21% and ee = 98% were obtained [79]. Studies using the _Corynespora cassicola_ DSM 62475 strain to transform both the racemic mixture of linalool and the pure (3_R_)-(--)-enantiomer have shown that the formation of cyclic oxygen derivatives of linalool is highly stereospecific. The products obtained from (\(\pm\))-linalool were _trans_-(2\(R\),5_R_) and _cis_-(2\(S\),5_R_)-furanoid linalool oxide and _trans_-(2\(R\),5_S_)-pyranoid linalool oxide. For the (3_R_)-(--)-enantiomer of linalool, the main products were _trans_-(2\(R\),5_R_)-furanoid linalool oxide and _trans_-(2\(R\),5_S_)-pyranoid linalool oxide [80].