title: Tetra-hydro-alstonine.
abstract: In the title compound, C21H24N2O3 [systematic name: methyl (20α)-16,17-dide-hydro-19α-methyl-18-oxayohimban-16-carb-oxy-l-ate], the mol-ecule adopts an L-type conformation. The crystal packing is governed by one N-H⋯π and one C-H⋯π inter-actions. The crystal cohesion is ensured by inter-molecular van der Waals contacts [shortest O⋯O contact = 3.199 (2) Å].
authors.affiliation: Laboratoire de Pharmacognosie, UMR CNRS 8638, Faculté des Sciences Pharmaceutiques et Biologiques de Paris Descartes, 4, avenue de l'Observatoire, 75270 Paris Cedex 06, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Cachet
authors.affiliation: Laboratoire de Pharmacognosie, UMR CNRS 8638, Faculté des Sciences Pharmaceutiques et Biologiques de Paris Descartes, 4, avenue de l'Observatoire, 75270 Paris Cedex 06, France.
authors.forename: François-Hugues
authors.initials: FH
authors.lastname: Porée
authors.affiliation: Laboratoire de Pharmacognosie, UMR CNRS 8638, Faculté des Sciences Pharmaceutiques et Biologiques de Paris Descartes, 4, avenue de l'Observatoire, 75270 Paris Cedex 06, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Michel
authors.affiliation: Laboratoire de Cristallographie et RMN biologiques, UMR CNRS 8015, Faculté des Sciences Pharmaceutiques et Biologiques de Paris Descartes, 4, avenue de l'Observatoire, 75270 Paris Cedex 06, France.
authors.forename: Pascale
authors.initials: P
authors.lastname: Lemoine