Methyl (1R,9S,10R,12S,13E,16S,18S)-13-ethylidene-10,18-dihydroxy-8,15-diazahexacyclo[14.2.1.0~1,9~.0~2,7~.0~10,15~.0~12,17~]nonadeca-2,4,6-triene-17-carboxylate