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Single crystal X-ray structures of cocrystals, 1·2 and 1·3, derived from U-shaped ureadicarboxylic acid (1) with 2-aminopyrimidine (2) and melamine (3), respectively, were examined. Cocrystals were obtained as a 1:1 mixture of 1 and the corresponding base. Two molecules of 1 and two molecules of the base were combined together via intermolecular H-bonding creating a supramolecularly assembled cyclic heterotetramer motif of rhombus shape. In the case of cocrystal 1·3, the cyclic heterotetramers were connected via H-bonding by utilizing a remaining amino group of melamine resulting in the formation of a tape of cyclic heterotetramer.

Utilizing hydrogen bonding between pyridine and benzoic acids, hydrogen-bonded ionic liquid crystals were prepared from pyridinylmethylimidazolium and alkoxy-substituted benzoic acids. Depending on the number of alkoxy substituents, smectic C (SmC), rectangular columnar (Colr), and cubic (Cub) phases were obtained from mono-, di-, and tri-substituted benzoic acids, respectively. These phases were investigated with X-ray diffraction, differential scanning calorimeter, and polarized optical microscopy.

Conformation of aromatic foldamers possessing three aromatic rings in a sequence of anthracene–phenylene–anthracene linked with iminodicarbonyl was examined. Their folding structures were confirmed by single crystal X-ray analysis. Two conformations, straight-zigzag and helically-zigzag conformations, were found depending on the substituents at the imide nitrogen atom. Induced circular dichroism originated in the interaction of the upper and bottom anthracene moieties was observed both in solution and in the solid state.

Anthracene derivatives possessing pentafluorobenzoyloxy moieties at 9- and 10-positions showed polymorphism affording two types of fluorescent crystals with blue and bluish green fluorescence in their crystalline state, respectively. Their single crystal X-ray structures showed that the degree of overlap of anthracene moieties was responsible for the difference in fluorescence. Fluorescence in the crystalline state originated in the dimer emission deduced from their excitation spectra.

Intramolecular pholocycloaddition of cyclopropene carboxylic acid allylic esters 1 results in an exclusive formation of 5-oxaspiro[2.4]hepta-4-ones 2, the hydrogen transferred rearrangement products, with induction of three stereogenic centers. Ring strain is crucial to alter the course of reaction from the [2+2] photocycloaddtion to the hydrogen transfer.

Thermal rearrangement of diastereomeric 7-vinylnorcaradienes 2 and 3 resulted in the formation of three products, two of which were derived from the vinylcyclopropane-cyclopentene rearrangement and the third from the Cope rearrangement. Almost identical product ratios from 2 and 3 suggested the existence of a common biradical as an intermediacy. The kinetic versus thermodynamic control of the rearrangement was achieved by the choice of the substituent (X) in norcaradienes 9.

A specific cleavage of the C1C7 bond, one of the three σ-bond of cyclopropane moiety, of norearadienes 1 was accomplished by acid catalyzed, dehydrative aromatization of the corresponding lactols to give 2H-pyran derivatives.

Duryne, 1 , a cytotoxic metabolite which inhibits the growth of both mouse and human tumor cell lines in vitro has been isolated from the marine sponge Cribrochalina dura . Its structure has been assigned by spectral methods.

The photosensitized oxygenations of various diazo compounds in the presence of oxygen atom acceptors were carried out. An electrophilicity of the intermediate was investigated.

The title compounds were isolated from a marine sponge collected off Okinawa. Their structures were determined by X-ray and shown to be 1-β-carbolines. Manzamine C was the 2-ethyl-N-azacycloundec-6-ene derivative, whereas manzamine B was more complex being the epoxy isomer of the free base of dihydromanzamine A.

4-Methyl-4-naphthoquinol and its 5-methyl derivative on treatment with per-Amberlyst 15 are converted to the corresponding cis-2,3-epoxides in high yields. The latter structure was determined by X-ray crystallography.

Fused ring alkaloids having the pyridol[4,3,2- mn ]acridine skeleton comprise a new class of marine natural products. 1a–h Their biological activity 1e and challenging structure elucidation make them an interesting group of compounds. In this paper we report the identification of four new cytotoxic and structurally related alkaloids: nordercitin ( 1 ), dercitamine ( 2 ), dercitamide ( 3 ), and cyclodercitin ( 4 ).

Manzamines E ( 2 ) and F ( 3 ) have been isolated as cytotoxic constituents of a sponge of the genus Xestospongia and the structures elucidated by the application of 2D-NMR tecniques and spectroscoplc comparison with manzamine A (1). Manzamine F was shown to be identical with keramamine B ( 4 ), the structure of which should therefore be revised as 3 .