Detection and determination of p-coumaroylated units in lignins.
The derivatization followed by reductive cleavage (DFRC) method cleaves alpha- and beta-ethers in lignins but leaves lignin gamma-esters intact. When applied to grasses, which contain p-coumarate esters on their lignins, esterified monolignol derivatives are released. Saturation of the p-coumarate double bond occurs during DFRC, so the released products are 4-acetoxycinnamyl 4-acetoxyphenylpropionates. Synthesis of the esters allowed determination of response factors for the released products. Maize and bamboo lignins released 221 and 38 micromol/g of p-coumarate-derived esters. The sinapyl ester was much more abundant than the coniferyl one. The bamboo and maize lignin S/G ratios in the conjugates were 12 and 38 times greater than those of the normal monomers released by DFRC, evidence of a strong selectivity for acylation of syringyl units. Of three possible biochemical mechanisms for incorporating p-coumarates into lignin, evidence is mounting that the process involves incorporation of preacylated monolignols into the normal lignification process.
Lu
F
F
U.S. Dairy Forage Research Center, Agricultural Research Service, U. S. Department of Agriculture, and Department of Forestry, University of Wisconsin-Madison, 53706, USA.
Ralph
J
J
D002625:Chemistry, Organic / Q000379:methods; D003373:Coumaric Acids / Q000032:analysis*; D004952:Esters / Q000032:analysis*; D004987:Ethers / Q000032:analysis*; D008031:Lignin / Q000737:chemistry*; D010084:Oxidation-Reduction; D006109:Poaceae / Q000737:chemistry
D003373:Coumaric Acids; D004952:Esters; D004987:Ethers; D008031:Lignin