Yoshio Sasada

The structure of tetronolide, the aglycone of antitumor antibiotic tetrocarcin

Abstract X-ray analysis has determined the structure of tetronolide, which has a unique spiro γ-lactone group.

Crystal structure of µ-octaethylporphinato-bis[dicarbonylrhodium(I)]

It is shown by X-ray analysis that the two RhI atoms in the title metalloporphyrin are located above and below the macrocyclic plane, the co-ordination of each metal being square planar.

X-Ray crystal structure of octaethylporphinium (monocation) tri-iodide

X-Ray analysis shows that in the porphyrin monocation one pyrrole ring, probably protonated, is tilted 14° from the plane through the other three pyrrole rings by the repulsions between the inner three hydrogen atoms.

The chemistry of phenalenium system—II: 7,8,2′,3′,4′,5′-Hexachloro-11-methoxy-6H-cyclopenta[a]pyrene-6-spiro-1′-cyclopenta-2′,4′-diene

Abstract 7,8,2′,3′,4′,5′-Hexachloro-11-methoxy-6H-cyclopenta[a]pyrene-6-spiro-1′-cyclopenta-2′,4′-diene 5 has been obtained by the reaction of phenalenone and 1,2,3,4-tetrachlorocyclopentadiene. The gross structure of 5 has been determined by the X-ray analysis. The ground-state properties of 5 were discussed from the spectroscopic data, dipole moment and bond lengths.

Studies of protein-nucleic acid interactions using model crystals

For the mutual recognition between protein and nucleic acid, specific interactions between the components of both polymers should be properly combined in a fitting scheme of secondary or tertiary structures. We call these combinations elementary interactions between protein and nucleic acid. The interactions were investigated using the model crystals that contain side chains of amino acid and a nucleic acid base. Taking C, T, U, A, and G as base and hydroxyl, carboxyl, carbamoyl, imidazolyl, phenyl, hydroxyphenyl, and indolyl groups as side chains of amino acid, several combinations were extensively studied. Interaction patterns between complementary base pairs and amino acids were also examined using ternary model systems. Several characteristics are observed in the model crystals, for instance, stabilization of stacking between the bases and histidine by the protonation of the latter, common hydrogen bonding patterns between bases and a hydroxyl or carboxyl group by reversal of donor-acceptor relationship or ionization. UV, NMR experiments and calculation by molecular orbital methods revealed energetic aspects of these interactions. A structural constraint is derived between the hydrogen bonds and the secondary structural fitting of an alpha-helical segment into the major groove of B-DNA. In terms of elementary interactions, stereochemical interpretations are given for the selectivity and enzymatic reaction of RNAase, binding of cro repressor to operator and initiation and elongation in the assembly of tobacco mosaic virus.

Absolute configuration of the alkaloid cularine: an X-ray structure determination

The structure of cularine has been determined by a three-dimensional X-ray crystal analysis of the methiodide, and the absolute configuration of the alkaloid has been assigned as (S).

Crystal structure of corynoline P-bromobenzoate

Crystals of the title compound (3) are monoclinic, space group P21/c with Z= 4 in a unit cell of dimensions: a= 12·598(88), b= 14·868(67), c= 13·592(79)A, β= 115·30(43)°. The structure was solved from diffractometer data by the heavy-atom method and refined by least-squares methods, to R 0·165 for 2008 observed reflexions. The B/C ring junction is cis-fused and rings B and C take the half-chair and the twist-half-boat conformations, respectively.

Crystalline-state reaction of cobaloxime complexes accompanying conformational change☆

Abstract In the crystals of some cobaloxime complexes, racemization of chiral group bonded to Co proceeds by X-ray irradiation without degradation of crystallinity. Racemization of methoxycarbonylethyl (mce) group has been examined for five cobaloxime complexes with different base as the second axial ligand, three of which did not give any indication of the reaction. Their crystal structures well explain the inactivity. Every stage of the change in the reactive crystals (base 4-chloropyridine, I; pyridine, II) has been revealed by X-ray analysis. In I, the mce groups suffer configurational and conformational changes at high temperature cooperatively. In II, rapid desolvation at room temperature is accompanied by conformational change of mce, and at 343 K random inversion occurs.