Diastereoselective synthesis of quaternary alpha-amino acids from diketopiperazine templates.
Davies SG., Garner AC., Ouzman JVA., Roberts PM., Smith AD., Snow EJ., Thomson JE., Tamayo JA., Vickers RJ.
Sequential enolate alkylations of (S)-N(1)-methyl-5-methoxy-6-isopropyl-3,6-dihydropyrazin-2-one and (S)-N(1)-p-methoxybenzyl-5-methoxy-6-isopropyl-3,6-dihydropyrazin-2-one proceed with excellent levels of diastereoselectivity (>90% de) affording quaternary alpha-amino acids in high enantiomeric excess (>98% ee) after deprotection and hydrolysis.