A cocrystal of 3α-hydroxytirucalla-8,24-dien-21-oic acid and 3β-fluorotirucalla-7,24-dien-21-oic acid (0.897:0.103)

The title compound, 0.897C30H48O3.0.103C30H47O2F is a co-crystal of two triterpenes isolated from the resin of Canarium schweinfurthiiand Engl. Both triterpenes consists of four trans-fused rings having chair/half-chair/half-chair and envelope conformations. The molecular conformations are stabilized by intramolecular C—H⋯O hydrogen bonds, forming rings of S(7) graph-set motif. In the crystal, molecules are linked by intermolecular O—H⋯O and C—H⋯O interactions, forming sheets parallel to (001). All atoms. excepting the axially-oriented hydroxyl group in the major component and the equatorially-oriented fluorine atom in the minor component, are overlapping.

The title compound, 0.897C 30 H 48 O 3 .0.103C 30 H 47 O 2 F is a cocrystal of two triterpenes isolated from the resin of Canarium schweinfurthiiand Engl. Both triterpenes consists of four transfused rings having chair/half-chair/half-chair and envelope conformations. The molecular conformations are stabilized by intramolecular C-HÁ Á ÁO hydrogen bonds, forming rings of S(7) graph-set motif. In the crystal, molecules are linked by intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO interactions, forming sheets parallel to (001). All atoms. excepting the axially-oriented hydroxyl group in the major component and the equatorially-oriented fluorine atom in the minor component, are overlapping.
The co-crystal was isolated during the phytochemical investigation of the dichloromethane soluble part of the resins of the medicinally important plant Canarium schweinfurthii of Cameroon. The plant has been used for the treatment of a wide range of ailments including malaria, fever and diarrhea (Atawodi, 2010;Dongmo et al., 2010). The refinement of the crystal structure revealed I and II as major (89.7%) and minor (10.3%) component, respectively with the difference that in II the axially oriented hydroxyl group attached to C3 has been replaced by the equatorially oriented fluorine atom. The asymmetric unit of the co-crystal ( Fig. 1) consists of the mixture of I (Fig. 2) and II (Fig. 3). The crystal structure of the major component I has already been reported and the space group (P3 1 21) and cell parameters were found to be similar to those previously reported (Mora et al.. 2001, Yousuf et al., 2011. However the minor component II was found to be a new triterpene. In both components the molecular structure showed that the trans fused rings  Table 1) and arranged parallel to the (001) plane (Fig.2).The absolute configuration was assigned on the basis of our recently published triterpene crystal data (Yousuf et al., 2011).

Experimental
The resin (100 g) of Canarium schweinfurthii Engl. was collected in Yaounde, Cameroon, in May 2010 and identified by Professor Noumi, a botanist at the Department of Biology, University of Yaounde-1. A voucher specimen (HNC 25918.) was deposited at the National Herbarium of Cameroon in Yaounde. The resin (100 g) of C. schweinfurthii was allowed to dry under shade and extracted with dichloromethane. The extract (70 g) was subjected to column chromatography over silica gel (300 g, 60 × 5 cm) eluting with hexane followed by a mixture of n-hexane-EtOAc in order to increase polarity. The fractions eluted were monitored by thin layer chromatography and similar fractions were combined to give seven fraction FrA-FrG. Fraction FrA (200 mg), obtained on elution with a mixture of n-hexane-EtOAc (8:2 v/v), was subjected to further column chromatography over silica gel (70 g, 60 cm 3 × 3, hexane-acetone equimolar solution) to yield crystals of the title compound. Recrystallization from n-hexane gave colourless crystals (60 mg).

Refinement
H atoms on the C of methyl, methylene, methine and oxygen were positioned geomatrically with C-H = 0.98-1.00 Å and O-H = 0.86 Å, respectively and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (CH 2 , CH) and 1.5U eq (CH 3 , supplementary materials sup-2 OH). A rotating group model was applied to the methyl groups. The crystal is a twin with twin law -1 0 0 0 -1 0 0 0 1 and BASF = 0.1815 (16). Friedel pairs were merged in the last refinement cycles.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. 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.