Gibberellin A4 monohydrate

The title compond, C19H24O5·H2O, has two gibberellin A4 molecules and two water molecules in the asymmetric unit. The A and B rings have chair conformations, whereas the C and D rings have envelope conformations; the two rings which contain the lactone and carbonyl bridge adopt chair and envelope conformations. The crystal structure is established by O—H⋯O hydrogen bonds and supported by C—H⋯O hydrogen bonds.

As shown in Fig. 1, there are two crystallographically independent (I) in the asymmeytric unit cell. The H atom at C2 and C8, the methylat C3, the hdroxyl at C5, the methano (C15) bridge and the carboxyl, all lie on the 'upper′ β face of the molecule, and the C=O group also toward the β face. Only the bridge that links the lactone and carbonyl has α stereochemistry. The A ring and the B ring have chair conformations, whereas the C ring and D ring have the envelope conformations, besides those, the two rings which contain the lactone and carbonyl bridge adopt chair and envelope conformations respectively. The H atom of axial hydroxyl group (O10) is aimed away from the ring system toward a water molecule, and the water (O12) hydrogen-bonding relates to the lactone carbonyl (O2). There exists two counterdirectional screw-related sets of helices, the hydroxyl and lactone carbonyl in related molecules within a given helix are involved in hydrogen bonds from a single water of hydration (O12-H12A···O2 and O12-H12B···O9), in turn, the oxygen (O12) of the same water accepts a hydrogen bond from the carboxyl group of a third screw-related molecule in an adjacent counter-directionally oriented helix (O10-H10···O12). Thus, water molecule acts both to brace the helix and to bridge it, alternately, to two different screw-related neighboring chains in a complex three-dimensional array.
The water molecules are linked to the GA4 molecules by O-H···O hydrogen bonds (Table 2), more over, weak C-H···O hydrogen bonds are obeserved between the gibberellin molecules to help increasing the stalitiy of the crystal (Fig. 2 & Table 2).

S2. Experimental
Gibberellin A4 (1 mmol, 0.33 g) was dissolved with 10 ml tetrahydrofuran and water (1:1) admixture, then heated to boiling and stirred for ten minutes. The resulting solution was cooled to the room temperature and the colorless crystals were collected after five days.

S3. Refinement
The H atoms attaching to O atoms and the H atoms of water were deduced from difference Fourier maps, and incorporated in refinement. Others were placed in calculated positions and allowed to ride on their parent atoms at distances of 0.98 (methyl), 0.99 (methylene), 1.00Å (methine), with U iso (H) values 1.2 times U eq of the parent atoms.
Because of the lack of atoms heavier than oxygen and the short measuring wavelength of Mo radiation, no useful supporting information absolute structure parameter could be refined.

Figure 1
The cell unit of (I) with atom labels, showing 40% probability displacement ellipsoids. The thin lines denote the hydrogen bonds.  The crystal packing of (I) viewed down along the c axis, hydrogen bonds shown as thin lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.