Identification of Polyketides in the Cuticular Waxes of Triticum aestivum cv. Bethlehem

Cuticular waxes are complex mixtures consisting mostly of very‐long‐chain aliphatics with single, primary functional groups. However, the waxes of many plant species also include aliphatics with one or more functional groups residing on subterminal or mid‐chain carbons. In the present work, the cuticular wax mixtures from flag leaf blades and peduncles of Triticum aestivum cv. Bethlehem were analyzed in a search for novel wax constituents with in‐chain functionalities, potentially of polyketide origin. The structures of compounds belonging to six different compound classes were elucidated using gas chromatography–mass spectrometry of various derivatives. Among them, a series of 2,4‐ketols was identified, with odd carbon numbers ranging from C25 to C37 and peaking at C33. The analogous C33 2,4‐diketone was identified as well, together with a pair of co‐eluting C31 mid‐chain β‐ketol isomers (16‐hydroxyhentriacontan‐14‐one and 14‐hydroxyhentriacontan‐16‐one), a pair of co‐eluting C30 mid‐chain α‐ketol isomers (15‐hydroxytriacontan‐14‐one and 14‐hydroxytriacontan‐15‐one), the corresponding C30 14,15‐diketone, and a pair of co‐eluting C31 ketones (hentriacontan‐14‐one and hentriacontan‐16‐one). All newly discovered structures contain ketone functional groups, with similar C13H27 and C15H31 alkyl chains on either side of the functionalities, thus resembling the previously reported very‐long‐chain β‐diketones dominating the wheat wax mixtures. Based on these structural characteristics, possible biosynthetic pathways leading to the newly identified polyketide‐like compounds are proposed.