Brazilian Conference on Natural Products
7th Brazilian Conference on Natural Product/ XXXIII RESEM Proceedings

Obtaining aroma compounds through biocatalytic processes emerge as a promising alternative once fewer residue is generated and mild conditions can be used with improved regioselectivity and enantioselectivity1. Lipases are widely used for the production of odoriferous enantiomeric esters for cosmetic and pharmaceutical industries2. The synthesis of high value-added chiral esters to be used as flavorings is an important field of research also in food biotechnology3. Based on the present demand of consumers towards natural flavors, the present study has intended to synthesize enantiomeric esters with odoriferous power, through biocatalysis. Two different esters were synthesized: n-2-octyl acetate and n-3-hexyl acetate using Candida antarctica lipase fraction B (CAL-B). The reactions were carried with 1 mmol of the alcohols (R,S)-2-octanol and (R,S)-3-hexanol and acetic acid as acyl donor. The reaction was initiated by addition of 50 mg of CAL-B in 2 mL of hexane. The vials were placed in an orbital shaker (180 rpm) at 30 °C. Samples (10 μl) were collected after 2, 4, 48, and 72 h of incubation. The degree of conversion (C) and the enantiomeric excess (ee) of (R,S)-2-octanol and (R,S)-3-hexanol were determined by GC-FID and GC-MS using the chiral selector β-DEX 120 capillary column (30 m x 0.25 mm x 0.25 µm).The alcohols were derivatized with MSTFA and a satisfactory resolution was achieved by an isoterme of 50ºC. The results showed that the conversion increased quickly at an initial period of 4h, and then slowly to a maximum value at 72h. After that, the molar conversion did not increase anymore, indicating that the reaction reached the equilibrium4. Maximum conversion of (R)-2-octyl acetate was of (54%) and (R)-3-hexyl acetate of (42.06%) after 72h of reaction. The enantiomeric excess was (>99%) for (R)-2-octyl acetate and also for (R)-3-hexyl acetate. Sontakke and Yadav4 used CAL-B for the acetylation of (R,S)-2-octanol and obtained a conversion of (42.6%) and (ee) of (71.8%) for (R)-2-octyl acetate. Shang et al.5 had a maximum molar conversion of (49.1%) and an enantiomeric excess of (95%), for (R)-2-octyl acetate, respectively. The catalytic activity of CAL-B was enantioselective, forming only (R)-2-octyl acetate and (R)-3-hexyl acetate enantiomers. This may be due to the non-recognition of the aesthetic stimulus (S), so it is not reactive or even impeditive in the enzyme structure and favored the difference between (R) and (S) enantiomers. This work shows that lipase-catalysed kinetic resolution with CAL-B is a very efficient procedure for the preparation of enantiomeric esters.