Synthesis and anthelmintic activity of 7-substituted 3,4a-dimethyl-4a,5a,8a,8b-tetrahydro-6H-pyrrolo[3′,4′:4,5]furo[3,2-b]pyridine-6,8(7H)-diones

The synthesis of racemic 7-substituted 3,4a-dimethyl-4a,5a,8a,8b-tetrahydro-6H-pyrrolo[3′,4′:4,5]furo[3,2-b]pyridine-6,8(7H)-diones 1-6 having strong in vivo efficacy against the parasitic nematode Haemonchus contortus Rudolphi in sheep is described. After separation of the racemic compound 2 by HPLC the absolute configuration of the most anthelmintically active (4aS,5aS,8aS,8bR)-enantiomer 2a was determined by single crystal X-ray analysis using its (4aS,5aS,8aS,8bR)-2a-CuCl2 (2:1)-complex.