Microbial Transformation of Calamintha glandulosa Essential Oil by Aspergillus niger

Abstract

A number of potentially useful compounds with various biological activities can be obtained from plant metabolites by microorganisms. In present research, essential oil of Calamintha glandulosa was subjected to the biotransformation process by mycromicete Aspergillus niger. GC/MS analyses of the original and biotransformed essential oil have revealed six(1-6) biotransformed compounds from one of the main component-limonene and one biotransformed product (7) originating from the less abundant component-thymol. Piperitone epoxide and piperitenone epoxide, the most abundant components of the original oil, were not biotransformed but gave three artefacts (A1, A2, B1) due to the acidic conditions formed in A. niger medium. Compounds 5, 6 as well as 7 have not been previously found as a biotransformation products of limonene (5 and 6) and thymol (7), respectively. New products (5, 6, and 7) together with the artefacts, were isolated by silica gel column chromatography followed by preparative silica gel thin layer chromatography, and their structures were established by a combination of 1D and 2D NMR spectra and GC/MS data. Biotransformation has one more confirmed as useful method, complementary to synthesis, for obtaining different type of molecules.