Synthesis of Enantiopure 10-Nornaltrexones in the Search for Tolllike Receptor 4 Antagonists and Opioid Ligands

摘要

10-Nornaltrexones (3-(cyclopropylmethyl)-4a,9-dihydroxy-2,3,4,4a,5,6-hexahydro-~1H-benzofuro[3,2-e]- isoquinolin-7(7aH)-one, 1) have been underexploited in the search for better opioid ligands, and their enantiomers have been unexplored. The synthesis of trans-isoquinolinone 2 (4-aH, 9-O-trans-9-methoxy-3-methyl-2,3,4,4a,5,6-hexahydro-~1Hbenzofuro[ 3,2-e]isoquinolin-7(7aH)-one) was achieved through a nonchromatographic optimized synthesis of the intermediate pyridinyl compound 12. Optical resolution was carried out on 2, and each of the enantiomers were used in efficient syntheses of the “unnatural” 4aR,7aS,12bR-(+)-1) and its “natural” enantiomer (?)-1. Addition of a 14-hydroxy (the 4a-hydroxy) group in the enantiomeric isoquinolinones, (+)- and (?)-2), gave (+)- and (?)-10-nornaltrexones. A structurally unique tetracyclic enamine, (12bR)-7,9-dimethoxy-3-methyl-1,2,3,7-tetrahydro-7,12b-methanobenzo[2,3]oxocino[5,4-c]pyridine, was found as a byproduct in the syntheses and offers a different opioid-like skeleton for future study.