The title compound, C(21)H(30)O, was isolated from the soft coral Sinularia sp. The mol-ecule contains four alicyclic rings, all trans-fused, among which three six-membered rings are in different distorted chair conformations while a five-membered ring assumes an envelope form.

The title compound, C15H19NO4, is the a product of the esterification of the corresponding carbonic acid with methanol. The mol-ecule comprises a fused tetra-cyclic system containing three five-membered rings (2-pyrrolidinone, tetra-hydro-furan and di-hydro-furan) and one seven-membered ring (azepane). The five-membered rings have the usual envelope conformations, with the quaternary C atom bei...

The title compound, C(37)H(50)N(2)O(3), is a benzyl ester derivative of oleanolic acid, a penta-cyclic triterpene, with a five-membered oxadiazole ring fused to the ring A. The triterpene A and C rings adopt slightly distorted half-chair conformations, whereas the remaining three six-membered rings are in chair forms.

In the title compound, C(37)H(38)N(4)O(6), four five-membered nitro-gen-bearing rings are nearly coplanar. Two N atoms in two these five-membered rings have attached H atoms, which contribute to the formation of intra-molecular N-H⋯N hydrogen bonds [N⋯N = 2.713 (5)-3.033 (6) Å].

The structure of the racemic title compound, C(10)H(15)NO(4), consists of a tricyclic skeleton comprising a six-membered piperidine ring and five-membered isoxazolidine and tetra-hydro-furan rings. The piperidine ring adopts a distorted chair conformation, while the isoxazolidine and tetra-hydro-furan rings have envelope conformations.

In the mol-ecule of the title compound, [Fe(C(5)H(5))(C(17)H(11)ClN(3))], the dihedral angles between the two five-membered rings and between the two six-membered rings are 3.28 (4) and 51.33 (4)°, respectively. In the crystal structure, inter-molecular N-H⋯N hydrogen bonds link the mol-ecules into centrosymmetric dimers.

The title compound, C(24)H(41)NO, is a new derivative of the anti-HIV steroid 17β-(N-tert-butyl-amino-carbon-yl)androst-4-en-3-one. There are four rings in the structure and these are trans-fused. The three six-membered rings exhibit chair conformations, while the five-membered ring adopts an envelope conformation.

The title compound, C(13)H(20)O(4)Si(2), is a siloxane-functionalized norbornane anhydride. Both five-membered heterocyclic rings of the mol-ecule have a planar structure, whereas the two five-membered aliphatic rings assume envelope conformations. Weak inter-molecular C-H⋯O hydrogen bonding is present in the crystal structure.

THE TITLE COMPOUND (SYSTEMATIC NAME 3-meth-oxy-24-methyl-9,19-cyclo-lanost-25-ene), C(32)H(54)O, is a triterpenoid which has been isolated from Skimmia laureola. The three six-membered rings adopt chair, slightly distorted half-chair and distorted boat conformations, and the five-membered ring adopts an envelope conformation. All the rings are trans fused.

In the title compound, C(15)H(23)N(3)O(4), the six-membered pyran, cyclo-hexane and trioxane rings adopt chair, chair and boat conformations, respectively, while the seven-membered rings adopt distorted boat and very distorted chair conformations. In the crystal, adjacent mol-ecules are connected by weak C-H⋯N and C-H⋯O inter-actions.