Asymmetric Synthesis of the ABC-Ring System of the Antitumor Antibiotic MPC1001

trans-4-Hydroxy-L-proline was converted into a tricyclic compound representing three contiguous rings of the anticancer antibiotic MPC1001. The tricyclic model contains the dihydrooxepin and diketopiperazine subunits, as well as one of the sulfur atoms of the natural product. The diketopiperazine unit was formed by a new method that involves cyclization of an enolate onto the carbonyl of a phenyl carbamate, and the dihydrooxepin ring was generated by using an acid-induced cyclization of an alcohol onto the beta-carbon of a vinylogous amide.