The Merck synthesis of -thienamycin

Thienamycin is an important antibiotic used clinically against a wide variety of pathogenic bacteria, including strains resistant to penicillins because of their production of the enzyme P-lactamase. 

An unusual feature of the asymmetric synthesis described here is the temporary destruction of the original stereogenic centre. 

The naturally occurring enantiomerically pure starting material is (5 )-aspartic acid, which is converted by standard means into the 

P-lactam (15). This forms a dianion on treatment with LDA which reacts with acetaldehyde to give a mixture of aldol products (16) and 

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