New synthesis of all four 1-amino-2-hydroxycyclohexanecarboxylic acids

This report describes a new synthesis of the four stereoisomers of 1-amino-2-hydroxycyclohexanecarboxylic acids [(1 S ,2 S )-, (1 R ,2 R )-, (1 S ,2 R )- and (1 R ,2 S )-c 6 Ser], four conformationally constrained serine (Ser) analogues, possessing a six-membered carbocyclic ring. Initially, we synthesised cis -c 6 Ser and trans -c 6 Ser in their racemic forms, using as key steps the Diels–Alder reactions of methyl 2-benzamidoacrylate with Danishefsky's diene and 1-methoxy-1,3-butadiene, respectively. The optically active forms were achieved by resolution methods.