SEPARATION AND IDENTIFICATION OF LIME CUTIN MONOMERS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND MASS-SPECTROMETRY

A recently developed HPLC technique has been used to identify 10 major monomers from potassium hydroxide hydrolysis and transesteridcation o f lime cutin, revealing 16-hydroxy-10-oxo-hexadecanoic and 10,16-dihyd roxyhexadecanoic acids as the major constituents. Solid-state C-13 NMR spectroscopy has also been used to examine the unreacted residues fol lowing hydrolytic treatment. For transesterification with methanolic b oron trifluoride, an alternative protocol using MS has been developed. Using HPTLC to separate epoxy and hydroxy fatty esters, and making a series of trimethylsilyl ether derivatives, the monomeric products hav e been subjected to analysis by GC-CI-mass spectrometry. Although GC c annot discriminate between positional isomers of oxo and dihydroxy fat ty acids, the parent ions and fragmentation patterns obtained with CI- mass spectrometry allow definitive identification of each isomer and r eveal five new constituents of the cutin biopolymer. Both the methodol ogy and the monomeric structures are compared with prior reports for c itrus fruit cuticle; implications for the molecular architecture and b iosynthesis of the lime cutin polymer are also discussed.