12a-b 15a-k. m= O 16a-e, m= l in vivo, so further modifications were carried out on 9 by ring closure at the positions depicted in Table 11. Compounds lla and llb, which contain a five- membered heterocyclic ring, showed potency equal to or less than that of 9 in the in vitro assay. On the other hand, llc and lld, which contain a six-membered heterocyclic ring, showed superior antagonist activity compared to 9. The 4-0xo-4H-l-benzopyran derivative ...
