Roland Prewo

The constitution of vertinolide, a new derivative of tetronic acid, produced by Verticillium intertextum☆

Abstract From the culture of Verticillium intertextrum a new tetronic acid derivative, vertinolide, has been isolated as the main constituent of the chloroform extract. Structure 1a was established for vertinolide by X-ray diffraction analysis. Vertinolide (1a) was also transformed to an O-methyl-(1b), an O-acetyl-(1c), a tetrahydro- (1d) and a tetrahydro-O-methyl-derivative (4). The spectroscopic properties of 1a, of its derivatives 1a, 1c, 1d and 4 as well as of three model compounds are compared and discussed.

Crystal structure of mozambioside, a diterpene glycoside of Coffea pseudozanguebariae

Abstract A diterpene glycoside of the furokaurane type has been isolated from the seeds of the caffeine-free coffee species Coffea pseudozanguebariae belonging to the section Mozambicoffea. This bitter-tasting compound named mozambioside is considered to replace caffeine with respect to chemical defence. Its configuration was determined by means of X-ray diffraction analysis.

On the structure of [η4-2,5-bis(trimethylsilyl)cyclopentadienone](η5-cyclopentadienyl)cobalt

X-ray diffraction study has been carried out on [η 4 -bis(trimethylsilyl)cyclopentadienone](η 5 -cyclopentadienyl)cobalt (I), the first example of a (η 4 -cyclopentadienone)(η 5 -cyclopentadienyl)cobalt complex with only two substituents on the cyclopentadienone ring. Complex I crystallizes in space group P 2 1 / c with four molecules in the unit cell and lattice parameters a 6.5259(5), b 12.2378(9), c 21.8397(15) A and β 90.442(7)°. Extended Huckel MO calculations are discussed for a simpler model, namely the parent cyclopentadienone complex (III).

Alstogustine and 19-epialstogustine, quaternary indole alkaloids from Alstonia angustifolia

Abstract Two new quaternary alkaloids, alstogustine and 19-epialstogustine, have been isolated from the stem bark of Alstonia angustifolia . The structure of 1 was determined by means of spectroscopic methods and X-ray analysis. The structure of 19-epialstogustine could be elucidated by comparison of its spectra with those of alstogustine and confirmed by chemical correlation. The absolute configurations of both alkaloids were established by direct comparison of their CD spectra with that of the known alkaloid, akuammicine.

Revision of the structures of rhazicine and rhazimine, two alkaloids from Melodinus acutiflorus

Abstract From the leaves of Melodinus acutiflorus the two alkaloids rhazicine and rhazimine were isolated and identified with known substances. However, based on extensive spectral and X-ray analysis their structures published earlier have to be revised.

Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 25. X-Ray structure determinations, crystallographic evidence for steric crowding, and correlation with acceleration of rates

X-Ray crystallographic structures are determined for seven N-benzylpyridinium salts including compounds possessing free, five-ring fused, and six-ring fused α-phenyl groups. Significant bond lengths, non-bonding distances, torsional and interplanar angles are determined and compared for the eight structures (the triphenyl derivative was found in two crystal environments). The results show steric overcrowding to an extent that parallels the kinetic displacement rates. However, the steric strain existing in all these molecules is relieved to different extents by different distortions in the different molecules. Nevertheless, crystallographic interatomic distances and angles are shown to be of potential utility in determining the type of mechanistic changes to be undergone, provided the appropriate parameters are selected.

N-2-(2-Bromo-4,5-dimethoxyphenyl)-1-(2,3,4-trimethoxyphenyl)ethylformamide

C20H24BrNO6, M(r) = 454.3, monoclinic, Cc, a = 27.479 (4), b = 5.128 (1), c = 21.811 (3) angstrom, beta = 139.35 (1)-degrees, V = 2002 (1) angstrom 3, Z = 4, D(x) = 1.51 Mg m-3, Mo K-alpha radiation, lambda = 0.71069 angstrom, mu = 2.07 mm-1, F(000) = 936, T = 130 K, R = 0.030 for 4151 observed reflections. The X-ray study confirms that in the solid state the structure of the title compound is similar to that inferred from chemical and spectroscopic evidence. Steric hindrance from different chemical groups is minimized by the adoption of a staggered conformation at the central C(8)-C(9) bond, with aryl groups in an anti disposition. There is a delocalized orbital along the N-C-O fragment of the N-formylamino group.

A novel photochemical rearrangement of allenic esters

The alkyl allenic esters (1a–c) on irradiation are found to afford the cyclobutenones (2a–c) while the phenyl ester (1e) affords the photo-Fries product (4).