A novel conformationally restricted analogue of 3-methylaspartic acid via stereoselective methylation of chiral pyrrolidin-2-ones

Conformationally restricted analogues of β-methylaspartic acid were easily prepared starting from chiral N-protected trans-3-amino-4-methoxycarbonyl pyrrolidin-2-ones. The key step of the synthesis was the methylation reaction at C-4, proceeding with high diastereoselection syn to the protected amino group lying at C-3 of the pyrrolidin-2-one ring.