The configuration of aurones

The configurations of 6-methoxyaurone prepared by the condensation of 6-methoxy- coumaran-3-one and benzaldehyde and of its photoisomer are assigned on the basis of chemical and NMR evidence.     

The absolute configuration of rhizobitoxine

The absolute configuration of rhizobifoxine, an amino acid produced by Rhizobium japonicum, has been determined by means of a new chiroptical method.     

The absolute configuration of streptonigrin

A theoretical study of the molecular circular dichroism (CD) of the antitumor antibiotic natural product streptonigrin is described, aiming at the secure assignment of its absolute configuration by comparison of the CD spectra predicted for M and P, with the experimental one. The stereostructure of streptonigrin was previously investigated by two other groups, yet leading to two different attributions. Although streptonigrin possesses two biaryl axes, only the ‘southern’ one is configurationally stable and thus responsible for the chiroptical properties, since the ‘northern’ AB-ring system of the molecule is kept in plane with ring C by hydrogen bonding. All computational methods applied within this work to simulate the CD spectrum—semiempirical approaches and time-dependent density functional theory (TDDFT)—consistently attribute the M-configuration to streptonigrin.     

The relative configuration of flavipucine

The relative configuration of the antibiotic flavipucine as inferred from a differential rearrangement reaction was confirmed by ozonolysis to a crystalline oxidoester amide identical with a specimen of this same compound prepared by synthesis.     

The absolute configuration of majoridine

Summary The oxidation of majoridine with chromium trioxide and lead tetraacetate with subsequent reduction of the oxidation product has yielded lochnerine and N-methyllochnerine and has thereby shown the absolute configuration of majoridine as 10-methoxy-O-acetyltetrafilicin.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 3, pp. 192–195, 1966     

The direct configuration interaction method with a contracted configuration expansion

A variant of the configuration interaction method is outlined. There are four characteristic features of the method. First, the freezing, contraction of coefficients in the configuration expansion. In the present approach Rayleigh-Schrödinger perturbation theory has been used for this purpose. Second, the use of the direct CI-method to construct hamiltonian matrix elements between functions with contracted coefficients, in only one sequential read of the molecular integrals. Third, a diagonalization of the resulting small matrix. Fourth, an important computational advantage in that only one CI-vector is needed in core storage instead of two as in the usual direct CI-method. The method has been programmed for the case of all single and double replacements from a spin-unrestricted Hartree-Fock determinant. Test calculations indicate that usually less than 2% of the correlation energy is lost because of the contraction of the CI-expansion. A possibility to avoid the major part of the integral transformation and work directly with atomic basis functions is also discussed.