(4R,5R,6S,7R,8S,9R,10S,13S)-7,8β-Epoxymomilactone-A

The title compound, C20H26O4, was extracted from Leucas Urticifolia, a wild Lamiaceae herb distributed in the Punjab, Baluchistan, Sindh and the Rajputana desert of Pakistan. The plant is utilized for various medicinal applications by the local community. The title compound is based on the pimarane–diterpene skeleton. The molecule exhibits an epoxy ring fused to momilactone-A, leading to a pentacyclic molecular structure. The absolute configuration was assigned by comparison with the crystal structure of momilactone, but needs further verification. The crystal structure is governed by four intermolecular hydrogen-bond interactions of the C—H⋯O type.

The title compound, C 20 H 26 O 4 , was extracted from Leucas Urticifolia, a wild Lamiaceae herb distributed in the Punjab, Baluchistan, Sindh and the Rajputana desert of Pakistan. The plant is utilized for various medicinal applications by the local community. The title compound is based on the pimaranediterpene skeleton. The molecule exhibits an epoxy ring fused to momilactone-A, leading to a pentacyclic molecular structure. The absolute configuration was assigned by comparison with the crystal structure of momilactone, but needs further verification. The crystal structure is governed by four intermolecular hydrogen-bond interactions of the C-HÁ Á ÁO type.
shoots with gur is used locally as an abortifacient up to 3 months of pregnancy. Infusion of the flowers are used in skin diseases. It is also used to treat piles. Other plants of the genera are also used in local remedies, e.g, the flowers of Leucas cephalotes are used to treat cold and cough while the entire plant has stimulant and insecticidal properties (Bhattecharjee, S. K., 2004). No work has been recorded for Leucas Urticaefolia although other plants of the genera have shown biologically and physiologically interesting classes of compounds (Misra et al., 1992;Misra et al., 1993;Misra et al., 1995).
Momilactone was originally extracted from the seed husk (Kato et al., 1973). The crystal structure was determined and the assignment of the absolute configuration was performed by several spectroscopic techniques. Synthesis of racemic (±)-Momilactone A and a related structure has been reported (Germain & Deslongchamps, 2002). The title compound (I), C 20 H 26 O 4 , is related to Momilactone A differing by one additional epoxy ring system therefore resulting in a pentacyclic molecular skeleton. There are three six membered rings: A (C1 to C5, C10), B (C5 to C10) and C (C8,C9,C11 to C14).
One five membered ring D (C4 to C6, O3, C18) with the lactone functional group is fused to ring A and ring B. The three membered epoxy ring E (C7, C8, O4) is fused to ring B in β-position. In analogy to the molecular structure of Momilactone the title compound was refined in the same absolute configuration with the chiral centers in the molecule being C4(R), C5(R), C6(S), C7(R), C8(S), C9(R), C10(S) and C13(S). Nevertheless, this configuration of course cannot be determined reliably using the experimental conditions of this investigation. Due to the methyl group attached to the common vertex of ring A and B at C10, these rings show an envelope conformation with C10 in an almost identical distance of -0.789 (4) Å from both planes. The dihedral angle between the planes (C1 to C5) and (C5 to C9) is 35.1 (2)° while the epoxy ring (C7, C8, O4) encloses dihedral angles of 39.8 (2)° and 74.9 (2)° with them, respectively. The puckering parameters (Cremer & Pople, 1975)  2002. In the crystal structure, the asymmetric unit is linked to four neighboring molecules through intermolecular C-H···O hydrogen bonds (Table 1). These H-bonds ( Fig. 1) seem to be effective in the stabilization of the structure. There is no significant π-π interaction.
supplementary materials sup-2 Experimental Leucas Urticaefolia was collected from the hills of Khanaspur, Pakistan. The plants were separated into stems (1.03 kg), inflorescence (256.56 g), leaves (812.34 g) and roots (421.34 g). Each of these fractions was dried under shade, powdered and extracted sequentially at room temperature for 72 h in each of the solvents such as hexane, chloroform, ethanol and water. Solvents were removed under reduced pressure. Each extract was extracted successively with n-hexane, chloroform, methanol and water as eluent in increasing order of polarity. Aluminium sheets precoated with silica gel 60 F254 (0.2 mm thick, E Merck) were used for TLC. Column chromatography was carried out on silica gel, 70-230 mesh. The title compound was taken from the water extract of the leaves.

Refinement
All H-atoms were found in Fourier synthesis and refined initially. However H atoms positioned geometrically resulted in the same values of refinement parameters.
In final refinement the coordinates of H-atoms connected to C16 were refined. The rest of H-atoms were positioned geometrically, with C-H = 0.93, 0.97, 0.96 Å for C15, methylene and methyl C-atoms and constrained to ride on their parent atoms. The thermal parameter of methyl H-atoms was taken 1.5 times while for all other H-atoms it was taken 1.2 times of the parent atoms.