Structure and absolute configuration of a high affinity 5-HT3 receptor antagonist, (5aS,9aS)-N-[(3S)-1-azabicyclo[2.2.2]octan-3-yl]-2-chloro-5a,6,7,8,9,9a-hexahydro-4-dibenzofurancarboxamide hydrochloride

The absolute configuration was established as (S,S,S) by the R-factor test and by careful measurement of 197 enantiomorph-sensitive Friedel pairs of reflections. The determination also confirms the absolute stereochemistry of (-)-3-aminoquinuclidine, a compound used in the preparation of the title material. The cyclohexane/tetrahydrofuran ring fusion is cis. The quinuclidine moiety has almost perfect threefold symmetry; the front and rear halves are twisted about this axis by 15 degrees. Quinuclidine-N--H ... Cl- and amide-N--H ... Cl- hydrogen bonds link screw-dyad-related molecules along the b axis.