sentences:  A ring opening leads to the formation of the short-lived intermediate 2,3-L-diaminopropanoic acid (DAPRO) which is then oxalylized by oxalyl-coenzyme A to form ODAP.ODAP can be synthesized from L-α,β-diaminopropionic acid and dimethyl oxalate at a pH of 4.5-5.Cupric oxide can be used to temporarily protect the α-NH2 group of the L-α,β-diaminoproprionic acid during the reaction.