Asymmetric Syntheses of the Macrocyclic Spermine Alkaloids (−)-(S)-Protoverbine, (−)-(S)-Buchnerine, and Their Naturally Occurring Congenial Alkaloids

Abstract

Asymmetric syntheses of the following 17-membered macrocyclic spermine alkaloids are presented: (−)-(S)-protoverbine (=(8S)-8-phenyl-1,5,9,13-tetraazacycloheptadecane-6-one; 1), (+)-(S)-protomethine (=(2S)-2-phenyl-1,5,9,14-tetraazabicyclo[12.3.1]octadecan-4-one; 2), (−)-(S)-buchnerine (=(8S)-8-(4-methoxyphenyl)-1,5,9,13-tetraazacycloheptadecane-6-one; 8), (+)-(S)-verbamethine (=(+)-(2S)-9-[(E)-phenylprop-2-enoyl]-2-phenyl-1,5,9,14-tetraazabicyclo[12.3.1]octadecan-4-one; 4), (−)-(S)-verbacine (=(−)-(8S)-1-[(E)-phenylprop-2-enoyl]-8-phenyl-1,5,9,13-tetraazacycloheptadecan-6-one; 3), (−)-(S)-verbasikrine (=(−)-(8S)-1-[(E)-3-(4-methoxyphenyl)prop-2-enoyl]-8-phenyl-1,5,9,13-tetraazacycloheptadecan-6-one; 26), (−)-(S)-isoverbasikrine (=(−)-(8S)-1-[(Z)-3-(4-methoxyphenyl)prop-2-enoyl]-8-phenyl-1,5,9,13-tetraazacycloheptadecan-6-one; 25), (+)-(S)-verbamekrine (=(+)-(2S)-9-[(E)-3-(4-methoxyphenyl)prop-2-enoyl]-2-phenyl-1,5,9,14-tetraazabicyclo[12.3.1]octadecan-4-one; 23), and (+)-(S)-isoverbamekrine (=(+)-(2S)-9-[(Z)-3-(4-methoxyphenyl)prop-2-enoyl]-2-phenyl-1,5,9,14-tetraazabicyclo[12.3.1]octadecan-4-one; 24). Effective methods for 1H-NMR determination of the enantiomeric purity in which (S)-2-hydroxy-2-phenylacetic acid and (S)-2-acetoxy-2-phenylacetic acid are used as shift reagents for 1, 8, and related macrocyclic alkaloids are described.