A nonracemic compound is synthesized and shown to assemble reversibly through hydrogen bonding to form a cyclic tetramer. The chiral arrangement of atoms in the individual pieces becomes amplified through self-assembly to yield multiple functional groups asymmetrically arranged within the cavity. The tetrameric capsule shows a special affinity for ketones and is able to discriminate between the...

The synthesis of a cyclic heptapeptide, delavayin-C, cyclo(gly-tyr-tyr-tyr-pro-val-pro) is described. The structure of this compound was established on the basis of analytical IR, (1)H NMR and FAB mass spectral data. The antibacterial and antifungal activities of this peptide are also described.

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.

A model compound bearing the C1–C17 fragment of carzinophilin was synthesized. The synthesis involved coupling reaction of a cyclic thioimidate with the 4H-oxazol-5-one derivative, ring-opening of the 4H-oxazol-5-one to furnish a dehydropeptide system, elaboration of the C1–C6 enolamide, and construction of the aziridine ring as key steps. q 2003 Elsevier Science Ltd. All rights reserved.

Cyclic eight-membered hydrogen-bonded rings exist in the title compound, C(5)H(7)N(2)(+).C(7)H(5)O(2)(-), involving the 2-aminopyridinium and benzoate ions. Each benzoate ion has two intramolecular hydrogen bonds. 2-Aminopyridinium benzoate ion pairs are linked by N-H...O hydrogen bonds, with an N...O distance of 2.8619 (14) A.

In the crystal structure of the title compound, C(16)H(13)NOS, mol-ecules are linked into cyclic centrosymmetric R(2) (2)(8) dimers via pairs of N-H⋯O hydrogen bonds. The seven-membered ring adopts a boat conformation.

The title compound, C21H21N3O2, adopts a J-shaped conformation which appears to be at least partially directed by a weak intra-molecular C-H⋯N hydrogen bond. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds into R 2 (2)(8) and R 2 (2)(14) cyclic dimers, which form a chain running parallel to the b axis.

3-Alkylpyridine alkaloids are very common secondary metabolites from marine sponges of the order Haplosclerida. Here, we report on the identification and synthesis of the first cyclic monomeric 3-alkylpyridinium alkaloid from natural sources. Due to the lack of a pure sample of the new compound, structure elucidation had to rely on HPLC and MS(n).

Cyclic tetrapyrroles are among the most potent compounds with activity against transmissible spongiform encephalopathies (TSEs; or prion diseases). Here the effects of differential sulfonation and metal binding to cyclic tetrapyrroles were investigated. Their potencies in inhibiting disease-associated protease-resistant prion protein were compared in several types of TSE-infected cell cultures....

The asymmetric unit of the title compound, C(6)H(13)N(2)O(+)·C(8)H(7)O(2) (-)·0.5H(2)O, comprises two isonipecotamide cations, two phenyl-acetate anions and a water mol-ecule of solvation. The hydrogen-bonding environments for both sets of ion pairs are essentially identical with the piperidinium and amide 'ends' of each cation involved in lateral heteromolecular hydrogen-bonded cyclic N-H⋯O as...