Abstract
Different mechanisms for the cyclisation of farnesyl pyrophosphate to patchoulol by the patchoulol synthase are discussed in the literature. They are based on isotopic labelling experiments, but the results from these experiments are contradictory. The present work reports on a reinvestigation of patchoulol biosynthesis by isotopic labelling experiments and computational chemistry. The results are in favour of a pathway through the neutral intermediates germacrene A and α-bulnesene that are both reactivated by protonation for further cyclisation steps, while previously discussed intra- and intermolecular hydrogen transfers are not supported. Furthermore, the isolation of the new natural product (2S,3S,7S,10R)-guaia-1,11-dien-10-ol from patchouli oil is reported.
Highlights
Patchouli oil, the essential oil of the shrub Pogostemon cablin, has a pleasant woody odour and is of high economic value for the perfumery and cosmetics industries
Using dimethylallyl diphosphate (DMAPP) and (E)- and (Z)-(4-13C,42H)isopentenyl diphosphate (IPP) [18] in conjunction with farnesyl diphosphate (FPP) synthase (FPPS) from Streptomyces coelicolor [19] and patchoulol synthase (PTS) (Supporting Information File 1, Figure S11), stereogenic centres of known configuration are introduced at the deuterated carbons
A second set of experiments made use of (R)- and (S)-(1-13C,12H)IPP [20] that were enzymatically converted with isopentenyl diphosphate isomerase (IDI) from E. coli [20,21], FPPS, and PTS (Figure S12 in Supporting Information File 1)
Summary
The essential oil of the shrub Pogostemon cablin, has a pleasant woody odour and is of high economic value for the perfumery and cosmetics industries. It is mainly composed of sesquiterpenes with patchoulol as the main compound Its planar structure was initially described as that of compound 1 (Figure 1) by Treibs [4], and later reassigned to structure 2 based on a total synthesis from camphor by Büchi [5]. The patchoulol synthase (PTS) has been purified from plant leaves and shown to convert farnesyl diphosphate (FPP) into compound 3 and several biogenetically related terpene hydrocarbons including α-patchoulene (4), β-patchoulene (5), α-bulnesene (6) and α-guaiene (7) (Figure 1) [7]. The enzyme was subsequently made available by cDNA gene cloning, revealing germacrene A (8), α-humulene (9), (E)-β-caryophyllene (10), seychellene (11) and pogostol (12) as further side products [8]
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