Monitoring the Chemical Profile in Agarwood Formation within One Year and Speculating on the Biosynthesis of 2-(2-Phenylethyl)Chromones

Abstract

Agarwood is highly valued for its uses as incense, perfume, and medicine. However, systematic analyses of dynamic changes of secondary metabolites during the process of agarwood formation have not yet been reported. In this study, agarwood was produced by transfusing the agarwood inducer into the trunk of Aquilaria sinensis, and changing patterns of chemical constituents, especially 2-(2-phenylethyl)chromones (PECs), in wood samples collected from the 1st to 12th month, were analyzed by GC-EI-MS and UPLC-ESI-MS/MS methods. Aromatic compounds, steroids, fatty acids/esters, sesquiterpenoids, and PECs were detected by GC-MS, in which PECs were the major constituents. Following this, UPLC-MS was used for further comprehensive analysis of PECs, from which we found that 2-(2-phenylethyl)chromones of flindersia type (FTPECs) were the most abundant, while PECs with epoxidated chromone moiety were detected with limited numbers and relatively low content. Speculation on the formation of major FTPECs was fully elucidated in our context. The key step of FTPECs biosynthesis is possibly catalyzed by type III polyketide synthases (PKSs) which condensate dihydro-cinnamoyl-CoA analogues and malonyl-CoA with 2-hydroxy-benzoyl-CoA to produce 2-(2-phenyethyl)chromone scaffold, or with 2,5-dihydroxybenzoyl-CoA to form FTPECS with 6-hydroxy group, which may serve as precursors for further reactions catalyzed by hydroxylase or O-methyltransferase (OMT) to produce FTPECs with diverse substitution patterns. It is the first report that systematically analyzed dynamic changes of secondary metabolites during the process of agarwood formation and fully discussed the biosynthetic pathway of PECs.

Chemical Profiles of Incense Smoke Ingredients from Agarwood by Headspace Gas Chromatography-Tandem Mass Spectrometry

“…Chemical constituents of agarwood have been intensively studied by several research teams [ 1 , 3 , 13 ]. Different extraction methods have been developed to determine chemical composition of essential oils and related compounds from agarwood chips using GC, GC-MS, solid phase microextraction, GC-flame ionization detector, GC-olfactometry, or comprehensive two-dimensional gas chromatography (GC×GC) [ 20 ].…”

“…Chemical constituents of agarwood have been studied by several research teams [ 1 , 3 , 13 ]. Previous studies identified chemical constituents of agarwood essential oils or organic solvent extracts with column chromatography or spectroscopic techniques [ 14 , 15 ].…”

“…Analysis of chemical constituents in the incense smoke produced by agarwood may be an approach to grading of agarwood. Most of past research studies determine chemical ingredients in agarwood solvent extracts [ 13 , 14 , 15 , 16 , 17 ]. However, analysis of chemical constituents in solvent extracts is not suitable in the case of agarwood because it is usually used to produce incense smoke.…”

Agarwood Induction: Current Developments and Future Perspectives

“…Until now, the PECs have only been found to be present in a few species of plants for example Bothriochloa ischaemum (Wang et al, 2001), Imperata cylindrical (Liu X. et al, 2013), Cucumis melo L. (Ibrahim, 2014), Gyrinops salicifolia (Shao et al, 2016), and Aquilaria species (Wu et al, 2012b; Yang et al, 2014a). Recently, a hypothetical scheme for the biosynthetic pathway of PECs was proposed by Liao et al (2018) based on in-dept analysis of agarwood chemical constituents using GC-EL-MS and UPLC-ESI-MS/MS methods. In their study, the PECs was found to be the major agarwood resin constituents, which is comprised mostly of flindersia-type 2-(2-phenylethyl) chromones (FTPECs).…”

“…In their study, the PECs was found to be the major agarwood resin constituents, which is comprised mostly of flindersia-type 2-(2-phenylethyl) chromones (FTPECs). The formation of FTPECs is further elucidated to be possibly catalyzed by type III polyketide synthase (PKs) through condensation of dihydro-cinnamoyl-CoA analogs and malonyl-CoA with 2-hydroxy-benzoyl-CoA to produce PEC scaffold that will subsequently be catalyzed by hydroxylases or O -methyltransferases (OMTs) to form structurally diverse FTPECs (Liao et al, 2018). Recent study showed that salinity stress could induce the biosynthesis of PECs in A. sinensis calli (Wang et al, 2016).…”