10,13-Dimethyl-16-oxo-4,5,6,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-1H-cyclopenta[a]phenanthren-17-yl acetate

In the title compound, C21H30O3, the five-membered ring adopts an envelope conformation, the cyclohexene ring displays a half-chair conformation and the two cyclohexane rings have normal chair conformations. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonding links the molecules into supramolecular chains running along [100].

In the title compound, C 21 H 30 O 3 , the five-membered ring adopts an envelope conformation, the cyclohexene ring displays a half-chair conformation and the two cyclohexane rings have normal chair conformations. In the crystal structure, weak intermolecular C-HÁ Á ÁO hydrogen bonding links the molecules into supramolecular chains running along [100].

Comment
Rocuronium is a nondepolarizing neuromuscular blocking agent, which produces neuromuscular blockade by competing with acetylcholine for cholinergic receptors at the motor end plate (Tuba et al., 2002;Auer, 2007). The title compound was obtained as an intermediate during our ongoing investigation of the synthese of rocuronium bromide. In this paper, we report the crystal structure of the title compound.
The molecular structure of the title compound is shown in Fig. 1. In the molecular structure, the cyclohexene ring displays a half-chair conformtion, the five ring adopts an envelope conformation, and two cyclohexane rings have the normal chair conformation. In the crystal structure weak intermolecular C-H···O hydrogen bonding links the molecules to form the supra-molecular chain running along the [1 0 0] direction (Table 1).

Experimental
The title compound was synthesized according to the procedure reported by Tuba et al. (1980) and by Newaz & Tcholakian (1984). Single crystals were obtained from a mixture of ethyl acetate and petroleum ether by slow evaporation at room temperature.

Refinement
All H atoms were placed in calculated positions, with C-H = 0.93-0.98 Å, and included in the final cycles of refinement using a riding model, with U iso (H) = 1.2 (1.5 for methyl groups) times U eq (C). Friedel paris were merged as no significant anomalous scattering. Fig. 1. The molecular structure of the title compound, showing the atom labelling scheme and 30% probability displacement ellipsoids.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds supplementary materials sup-3 in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.