Withanolides from Physalis angulata L.

The chemical structures of two withanolides, isolated from the leaves of Physalis angulata by column chromatography, were studied. The isolated compounds are (17S,20R,22R,24R,25S)-5β,6β:20,24-diepoxy-4β,25-dihydroxy-1-oxowith-2-en-26,22-olide and (20R,22R)-5α,14α,20-Trihydroxy-1-oxo-6α,7α-epoxywitha-2-enolide.


Chemical context
The genus Physalis belongs to the nightshade family of plants and is widely distributed in subtropical and tropical regions around the world. Some Physalis species are important in the diet because of their edible fruits. Phytochemical and pharmacological studies show that in plants of the genus Physalis, the main biological substances are withanolides (Huang et al., 2020). The fruits of Physalis angulata L. are edible, traditionally collected from wild populations, but the plant is now widely cultivated. In different countries of the world the fruits, roots and leaves of Physalis angulata L. are used in folk medicine as a treatment for various diseases (Salgado & Arana, 2013). The main secondary metabolites of Physalis angulata are withanolides, which are highly variable in chemical structure and exhibit interesting pharmacological activity (Ray & Gupta, 1994;Figueiredo et al., 2020;Sá et al., 2011;Pinto et al., 2016). The plant Physalis angulata is widespread in Uzbekistan and its reserves are sufficient for industrial use (Vasina et al., 1990).
To study the chemical structure of withanolides, leaves of Physalis angulata collected in the Tashkent region were used. Isolation of withanolides from the leaves of Physalis angulata ISSN 2056-9890 and separation of components into individual substances was carried out by column chromatography. The isolated compounds were identified as physangulide B chloroform solvate (I) and 14-hydroxyixocarpanolide (II).
In both molecules, ring C adopts a chair conformation and ring D an envelope conformation with atom C13 as the flap.
Ring A exhibits a half-chair conformation, but differs slightly in the arrangement of atoms. The C1-C4 fragment is planar with r.m.s deviations of 0.0045 Å for I and 0.034 Å for II. The deviations of atoms C5 and C10 atoms from this plane are À0.225 (7) and 0.291 (7) Å , respectively, for I and À0.478 (7) and 0.280 (7) Å for II.
In the molecule of I, atoms of ring B are located in one plane (with an r.m.s deviation of 0.0132 Å ), except for C8 which deviates from the plane of the remaining atoms by 0.666 (4) Å . A similar envelope conformation for ring B is observed in II. Here, the C5-C9 atoms are located in one plane with an accuracy of 0.0643 Å , atom C10 being displaced from the plane through the remaining atoms by 0.696 (4) Å . This difference in the arrangement of atoms in planes is explained by the position of the epoxy bridge, which is located in the -position for I and the -position for II.

Supramolecular features
In both crystal structures, intermolecular hydrogen bonds of the O-HÁ Á ÁO type are observed, which link the molecules along the c-axis direction. In compound I, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds are observed between molecules of physangulide B (Table 1). O4-H4Á Á ÁO26 and O25-

Figure 2
Molecular structure of the 14-hydroxyixocarpanolide (compound II), including atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 1
Molecular structure of the chloroform solvate of physangulide B (compound I), including atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ) for (I). H25Á Á ÁO56 hydrogen bonds are involved in the formation of an infinite chain along the c-axis (Fig. 3). In addition, the chloroform molecule participates in a hydrogen bond with the oxygen atom O26 of the lactone fragment. A similar hydrogen bond with a solvate molecule (methanol) is observed in the structure of the acetyl derivative of physangulide B (FUQKAF; Maldonado et al., 2015). Similar intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds are observed in the structure of II (Table 2). The formation of an infinite O20-H20Á Á ÁO5 hydrogen-bonded chain is shown in Fig. 4. Paired hydrogen bonds are observed between molecules, which extend along the c-axis direction.

Synthesis and crystallization
Isolation of individual substances from the leaves of Physalis angulata Collected dried leaves (4 kg) of Physalis angulata L. were poured into cold water and heated to boiling. The hot mass was squeezed out through a canvas. The plant was again poured into cold water, heated, and the hot mass was squeezed out through the canvas again. The water extract was distilled until the volume decreased to 3 L. Chloroform (3 L) was poured into the received solution and substances were extracted. From the chloroform layer, insoluble and soluble substances (25 g) were isolated. To the isolated dry mass, 0.5 L of chloroform were added and the solution was filtered (the mass of the insoluble compounds was 5.8 g). From the filtrate after distillation, 19.2 g of compounds were isolated. The compounds isolated from the filtrate were loaded onto a column containing 0.5 kg of silica gel (Silica gel 60, 0.063-0.1 mm, Merck). The sums of substances were eluted with system 1 (chloroform:methanol 99:1) to produce fractions 1-5, and eluted with system 2 (chloroform:methanol 97:3) to produce fractions 5-9. The process was monitored by thin layer chromatography (Silica gel on TLC Al foils, fluorescent indicator 254 nm). Fractions 2-4 (6.8 g) and 6-8 (4.0 g) were shown by TLC to consist of individual substances.

Figure 3
Hydrogen bonding in the crystal structure of I (the molecules are crosslinked along the c axis).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The H atoms bonded to C atoms were placed geometrically (with C-H distances of 0.98 Å for CH, 0.97 Å for CH 2 , 0.96 Å for CH 3 and 0.93 Å for C ar ) and included in the refinement in a riding-motion approximation with U iso (H) = 1.2U eq (C) [U iso = 1.5U eq (C) for methyl H atoms]. The hydrogen atoms on the O atoms were located in difference-Fourier maps and refined freely.  For both structures, data collection: CrysAlis PRO (Rigaku OD, 2018); cell refinement: CrysAlis PRO (Rigaku OD, 2018); data reduction: CrysAlis PRO (Rigaku OD, 2018). Program(s) used to solve structure: SHELXS7 (Sheldrick, 2008) for (II). For both structures, program(s) used to refine structure: SHELXL2014/8 (Sheldrick, 2015); molecular graphics: XP (Sheldrick, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 2008), PLATON (Spek, 2020) and publCIF (Westrip, 2010)′.   (6) 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 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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) (2) 0.0678 (9)      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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1