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3-Oxoolean-1-en-28-oic acid, isolated from the bark of Walsura pinnata Hassk, crystallized from n-hexane as an n-hexane 0.25-solvent 0.25-hydrate, C30H46O3·0.25C6H14·0.25H2O. There are two independent mol­ecules in the asymmetric unit of the title compound. The three six-membered cyclo­hexane rings in each mol­ecule adopt chair conformations and the carboxyl substituent occupies an axial/equatorial position. The two independent mol­ecules are linked by a pair of O—Hcarbox­yl⋯O hydrogen bonds into a dimer. The n-hexane mol­ecule is disordered about a twofold rotation axis and the water mol­ecule lies on a twofold rotation axis. In addition, the cyclo­hexone carbonyl group of one of the independent mol­ecules is disordered over two sites with occupancies of 0.75 and 0.25.

In the mol­ecule of pinnatane A, C30H48O3, isolated from the bark of Walsura pinnata Hassk, the four cyclo­hexane rings adopt chair conformations; the carboxyl and hydr­oxy substituents occupy axial positions. The cyclo­hexene ring is envelope-shaped. Adjacent mol­ecules are linked by O—H⋯O hydrogen bonds into a chain running along the c axis.

The title compound, C30H50O5, was isolated from the bark of Aglaia smithii. There are two independent mol­ecules in the asymmetric unit that differ in the orientation of the isopropenyl group attached to the cyclo­hexane ring. The cyclo­hexane rings in both mol­ecules adopt chair conformations, whereas the cyclo­pentane and tetra­hydro­furan rings adopt envelope conformations. The independent mol­ecules are linked into a layer parallel to (010) by O—H⋯O hydrogen bonds.

The title dammarane tritepene, 3α,20(S)-dihy­droxy­dammar-24-ene, which crystallized out in a hydrated form, C30H52O2.1.075H2O, was isolated from the Aglaia eximia bark. The three cyclo­hexane rings adopt chair conformations. The cyclo­pentane has an envelope conformation with the quaternary C at position 14 as the flap atom with the maximum deviation of 0.288 (2) Å. The methyl­heptene side chain is disordered over two positions with 0.505 (1):0.495 (1) site occupancies and is axially attached with an (+)-syn-clinal conformation. The hydroxyl group at position 3 of dammarane is in a different conformation to the corresponding hydroxyl in Dammarenediol II. In the crystal, the dammarane and water mol­ecules are linked by ODammarane—H⋯Owater and Owater—H⋯ODammarane hydrogen bonds into a three-dimensional network.

In each of the two independent indene-4-spiro­pentane mol­ecules in the asymmetric unit of the title 2:1 adduct, C19H18N6·0.5C5H4OS, the cyclo­hexene ring adopts a half-chair conformation and the cyclo­pentene and cyclo­pentane rings adopt envelope conformations. The mean plane through the cyclo­hexene/cyclo­pentene fused system is aligned at a dihedral angle of 77.9 (1)° with respect to the mean plane through the cyclo­pentane ring in one mol­ecule and 87.0 (1)° in the other. In the crystal, adjacent indene-4-spiro­pentane mol­ecules are linked by N—H⋯N hydrogen bonds into a three-dimensional network. The spaces within the network are occupied by the thio­phene-2-carbaldehyde mol­ecules. The thio­phene-2-carbaldehyde unit is disordered over two positions of equal occupancy. The crystal studied was found to be a non-morohedral twin with two minor twin components of 18.4 and 9.7%.

The title seco-dammarane triterpenoid, C27H42O4 (systematic name: 3-{(3S,3aR,5aR,6S,7S,9aR,9bR)-6,9a,9b-trimethyl-3-[(R)-2-methyl-5-oxotetra­hydro­furan-2-yl]-7-(prop-1-en-2-yl)dodeca­hydro-1H-cyclo­penta­[a]naphthalen-6-yl}propanoic acid), has been isolated for the first time from the seeds of Aglaia forbesii. The mol­ecule has three fused rings and all rings are in trans-fused. The two cyclo­hexane rings are in standard chair conformations and the cyclo­pentane ring adopts an envelope conformation. Its absolute configuration was determined by the refinement of the Flack parameter to 0.26 (17). In the crystal, mol­ecules are linked into chains along [010] by O—H⋯O hydrogen bonds.

The title compound, C28H44O4·0.56H2O, is a co-crystal of methyl isoeichlerialactone monohydrate as the major component and methyl isoeichlerialactone as the minor component in a 0.55778 (3):0.44222 (3) ratio. The conformations of both components are identical except for that of the –COOCH3 group of the methyl propanoate side chain on the cyclo­hexane ring which is positionally disordered over two orientations. The mol­ecule of methyl isoeichlerialactone has three fused rings and all rings are trans-fused. The two cyclo­hexane rings are in standard chair conformations and the cyclo­pentane ring adopts an envelope conformation. In the crystal, weak C—H⋯O inter­actions link methyl isoeichlerialactone mol­ecules into screw chains along [010]. The crystal structure is further stabilized by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.

The asymmetric unit of the title compound, C32H51N3O3, consists of two crystallographically independent mol­ecules, A and B; the 2-methyl­pentane group of mol­ecule A and the propane group of mol­ecule B are each disordered over two sets of sites, with refined site-occupancies of 0.825 (5):0.175 (5) and 0.630 (18):0.370 (18), respectively. In both mol­ecules, the three cyclo­hexane rings in the steroid fused ring systems adopt chair conformations while the cyclo­pentane rings adopt envelope and twist conformations in mol­ecules A and B, respectively. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds link the two independent mol­ecules together, generating R 2 1(7) and R 2 2(8) ring motifs.

The asymmetric unit of the title compound, C23H22N2O2, contains two independent mol­ecules, A and B. The cyclo­hexane ring of mol­ecule B is disordered, with occupancies for the major and minor conformers of 0.570 (9) and 0.430 (9), respectively. The cyclo­hexane ring adopts a boat conformation in mol­ecule A and in the major conformer of mol­ecule B, and a chair conformation in the minor conformer of mol­ecule B. In both independent mol­ecules, one of the dihydro­pyran rings adopts a boat conformation while the other is in a half-chair conformation. The dihedral angle between the pyrazole and phenyl rings is 16.0 (1)° in mol­ecule A and 12.9 (1)° in mol­ecule B. The crystal packing is stabilized by C—H⋯O and C—H⋯N inter­molecular hydrogen bonds.

The asymmetric unit of the title compound, C30H48ClN3O, contains two mol­ecules, A and B. In both mol­ecules, the three cyclo­hexane rings in the steroid fused ring systems adopt chair conformations, while the cyclo­pentane rings adopt envelope and twist conformations in mol­ecules A and B, respectively. In mol­ecule B, the cyano group is disordered over two orientations with refined site-occupancies of 0.593 (8) and 0.407 (8). An intra­molecular C—H⋯N inter­action forms an S(10) ring in both mol­ecules. In the crystal, mol­ecules are linked by N—H⋯O, C—H⋯O and C—H⋯N inter­actions, resulting is chains propagating along the a-axis direction.

The asymmetric unit of the title compound, C27H45ClO, consists of two crystallographically independent mol­ecules. In both mol­ecules, the three cyclo­hexane rings in the steroid fused-ring systems adopt chair conformations, while the cyclo­pentane ring adopts a half-chair conformation in one mol­ecule and an envelope conformation in the other. In the crystal, the mol­ecules are linked into a two-dimensional network by weak C—H⋯O hydrogen bonds. The crystal studied is a nonmerohedral twin with a refined ratio of twin components of 0.264 (3):0.736 (3).

In the title compound, C23H34O4, the C/D and D/E rings are trans fused and the A/B ring possesses an anti fusion. The two cyclo­hexane rings adopt a chair conformation while the cyclo­hexene ring exhibits a half-chair conformation. The cyclo­pentane ring displays an envelope conformation with the C atom bearing the methyl group as the flap. In the crystal, the mol­ecules are linked by O—H⋯O hydrogen bonds, forming chains along the b axis.

In the title mol­ecule, C30H52O4, the three six-membered rings are in chair conformations, the cyclo­pentane ring is in an envelope form and the tetra­hydro­furan ring has a conformation inter­mediate between half-chair and sofa. In the crystal, mol­ecules are linked by inter­molecular O—H⋯O hydrogen bonds into helical chains along [100]. Two intra­molecular O—H⋯O hydrogen bonds are also present. One C atom of the tetrahydrofuran ring and its attached H atoms are equally disordered over two sets of sites.

In the deca­hydro­phenanthrenone ring system of the title compound, C27H44O, the two cyclo­hexane rings adopt chair conformations, whereas the cyclo­hexene ring adopts an envelope conformation. The cyclo­pentane ring is twisted. In the crystal structure, mol­ecules are stacked along the a axis, but no significant inter­molecular inter­actions are observed.

The title compound, C15H20O3, a sesquiterpene lactone, was isolated from the aerial parts of Carpesium minus Hemsl. (Compositae). The mol­ecule is composed of three rings, with the two cyclo­hexane rings in chair conformations and the cyclo­pentane ring adopting a twist conformation. The A/B ring junction is trans-fused. The absolute configuration shown has been arbitrarily assigned. In the crystal, mol­ecules are linked into [100] chains by O—H⋯O hydrogen bonds.

The title quassinoid compound, C20H24O9·CH3OH·2H2O, is a natural eurycomanone isolated from the roots of Eurycoma longifolia. The mol­ecules contain a fused five-ring system, with one tetra­hydro­furan ring adopting an envelope conformation, one tetra­hydro­pyran-2-one ring in a screw boat conformation, one cyclo­hexenone ring in a half-chair conformation and two cyclo­hexane rings in chair conformations. Intra­molecular C—H⋯O inter­actions generate S(5) ring motifs and an O—H⋯O inter­action generates an S(7) ring motif. In the crystal, mol­ecules are linked via inter­molecular O—H⋯O inter­actions along the b axis and further stacked along a axis. The absolute configuration of the title compound was inferred from previously solved structures of its analogues.

The title compound, C26H28N2O9·1.5H2O, the product of an acid-catalysed Wagner–Meerwein skeletal rearrangement, crystallizes as a sesquihydrate with the O atom of one of the two independent water mol­ecules occupying a special position on a twofold axis. The organic mol­ecule comprises a fused penta­cyclic system containing two five-membered rings (cyclo­pentane and tetra­hydro­furan) and three six-membered rings (piperidinone, tetra­hydro­pyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered piperidinone and tetra­hydro­pyridine rings adopt boat and sofa conformations, respectively. In the crystal, there are three independent O—H⋯O hydrogen bonds, which link the organic mol­ecules and water mol­ecules into complex two-tier layers parallel to (001). The layers are further linked into a three-dimensional framework by attractive inter­molecular carbon­yl–carbonyl inter­actions.

In the title compound, C31H23NO2S, the pyrrolidine ring adopts an envelope conformation (with the spiro C atom as the flap), while the thia­zolidine ring and the two cyclo­pentane rings adopt twisted conformations. The mean plane through the hexa­hydro­pyrrolo­[1,2-c]thia­zole ring [r.m.s deviation = 0.400 (1) Å] forms dihedral angles of 76.83 (4), 80.70 (5) and 79.00 (4)° with the benzene ring and the mean planes of the dihydro­acenaphthyl­ene and the dihydro­indene rings, respectively. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds into sheets lying parallel to the bc plane. One of the ketone O atoms accepts three such bonds. Weak C—H⋯π inter­actions are also observed.

The title compound, C14H18N2O, was synthesized by the reaction of cyclo­hexa­none and 2-amino-5-methyl­benzonitrile. In the mol­ecule, the cyclo­hexane ring displays a chair conformation, whereas the 1,3-diaza­cyclo­hexane moiety of the bicyclic system has a sofa conformation with the spiro C atom displaced by 0.603 (2) Å from the rest of the atoms of the 1,3-diaza­cyclo­hexane ring [planar within 0.052 (2) Å]. Mol­ecules are linked into centrosymmetric dimers via N—H⋯O hydrogen bonds.

In the title mol­ecule, C34H53BrO4, all the cyclo­hexane rings adopt chair conformations, while the cyclo­pentane ring adopts an envelope conformation. In the crystal, weak inter­molecular C—H⋯O hydrogen bonds link the mol­ecules into corrugated sheets parallel to the ab plane.

The title compound, C16H17NOS2, consists of a carbazole skeleton with tetra­hydro­furan and dithiol­ane rings. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 1.57 (15)°. The cyclo­hexenone and tetra­hydro­furan rings have envelope conformations, while the dithiol­ane ring adopts a twist conformation. In the crystal structure, pairs of weak inter­molecular N—H⋯S hydrogen bonds link the mol­ecules into centrosymmetric dimers with R 2 2(16) ring motifs. Weak C—H⋯π inter­actions may further stabilize the structure.

The asymmetric unit of the title xanthene compound, C25H30O5, contains two mol­ecules in which the pyran ring and the dimeth­oxy­phenyl ring are nearly perpendicular to one another [dihedral angles = 86.81 (8) and 84.45 (9)°]. One of the meth­oxy groups in one mol­ecule is twisted away from the phenyl ring [C—O—C—C torsion angle = −103.40 (16)°]. The pyran ring adopts a boat conformation whereas the two fused cyclo­hexane rings adopt envelope conformations in both mol­ecules. In the crystal, mol­ecules are linked into a three-dimensional network by C—H⋯O hydrogen bonds.

In the title compound, C20H22O5, an S(6) ring motif is formed by an intra­molecular C—H⋯O hydrogen bond, which contributes to the stabilization of the mol­ecule. In the xanthene system, the cyclo­hexane ring adopts a chair conformation, the cyclo­hexene ring adopts a half-boat conformation and the tetra­hydro­pyran ring adopts a half-chair conformation. The mean plane of the four essentially planar atoms of the tetra­hydro­pyran ring [r.m.s deviation = 0.092 (1) Å] forms a dihedral angle of 64.13 (6)° with the mean plane of the meth­oxy­phenyl group. In the crystal, inter­molecular O—H⋯O and weak C—H⋯O hydrogen bonds link mol­ecules into chains along the a axis, which are further stabilized by C—H⋯π inter­actions.

The title compound, the product of an acid-catalysed Wagner–Meerwein skeletal rearrangement, crystallizes as an ethanol monosolvate, C20H21NO8·C2H6O. The title mol­ecule comprises a fused tricyclic system containing two five-membered rings (cyclo­pentane and tetra­hydro­furan) in the usual envelope conformations and one six-membered ring (piperidinone) adopting a flattened twist–boat conformation.

The title compound, C23H18N2O6, is the product of an intra­molecular thermal cyclo­addition within 1-malein-2-[(E)-2-(2-fur­yl)vin­yl]-4-oxo-3,4-dihydro­quinazoline. The mol­ecule comprises a previously unknown fused penta­cyclic system containing two five-membered rings (2-pyrrolidinone and furan) and three six-membered rings (benzene, 2,3-dihydro-4-pyrimidinone and dihydro­cyclo­hexa­ne). The central five-membered pyrrolidinone ring has the usual envelope conformation. The six-membered dihydro­pyrimidinone and dihydro­cyclo­hexane rings adopt a half-boat and a half-chair conformation, respectively. The dihedral angle between the planes of the terminal benzene and furan rings is 45.99 (7)°. In the crystal, O—H⋯O hydrogen bonds link the mol­ecules into centrosymmetric dimers. Weak C—H⋯O hydrogen bonds consolidate further the crystal packing, which exhibits π–π inter­actions, with a short distance of 3.556 (3) Å between the centroids of benzene rings of neighbouring mol­ecules.