Stereochemical studies on cyclic peptides: Detailed energy minimization studies on hydrogen bonded all-trans cyclic pentapeptide backbones.

Conformational studies have been carried out on hydrogenbonded all-trans cyclic pentapeptide backbone· Application of a combination of grid search and energy minimization on this system has resulted in obtaining 23 minimum energy conformations, which are characterized by unique patterns of hydrogen bonding comprising of ßand γ-turns. A study of the minimum energy conformations vis-a-vis non-planar deviation of the peptide units reveals that non-planarity is an inherent feature in many cases· A study on conformational clustering of minimum energy conformations shows that the minimum energy conformations fall into 6 distinct conformational families· Preliminary comparison with available X-ray structures of cyclic pentapeptide indicates that only some of the minimum energy conformations have formed crystal structures· The set of minimum energy conformations worked out in the present study can form a consolidated database of prototypes for hydrogen bonded backbone and be useful for modelling cyclic pentapeptides both synthetic and bioactive in nature·

Lipid composition of brain regions during chronic maternal alcohol treatment and withdrawal in the rat.

The lipid composition of whole brain, cerebrum, cerebellum and brain stem was studied in rat pups exposed to alcohol during prenatal and postnatal period and subsequent withdrawal or continuation during postweaning period. The concentrations of cholesterol and galactolipids were increased in the whole brain and brain regions of the pups exposed to alcohol. Even after 6 weeks of withdrawal from alcohol during postweaning period, the lipid levels were significantly higher compared to the controls. These observations suggest possible alterations in the functions of CNS related to membrane integrity.

Standard dimensions for cis N-methyl peptide unit and flexibility of cis peptide units.

The mean dimensions of the cis N-methyl peptide unit have been arrived at by analysing the crystal structure data on compounds containing such units. These dimensions can be used as standard in conformational studies on cyclic peptides. While the bonds meeting at C are almost coplanar, those meeting at Ν show a slight pyramidal disposition. A comparison of the dimensions of the normal and N-methylated cis peptide units show that there are perceptible differences in the parameters connected with N. In addition, the flexibility of the cis peptide unit has been analysed by studying the distribution of the parameters in different classes of compounds such as cyclic di, tri and higher peptides. The salient features are: (i) The angle CαCN in cyclic dipeptide and the angle CδNCα in higher peptides tend to be lower, when the peptide unit is associated with a prolyl residue; (ii) in cyclic tripeptides the internal angles viz., CαCN and CNCα are significantly larger thereby increasing the intra-annular space; (iii) the bond Cα-C is distinctly shorter when it occurs in cyclic dipeptides. The results lead to the conclusion that the cis peptide unit takes up a need-based flexibility in its dimension.

Cyclic peptides––Small and big and their conformational aspects.

Cyclic peptides form an interesting class of compounds for study by conformational analysis, by virtue of their unique conformational features and biological properties. The small cyclic peptides having 3–6 peptide units in their ring, show a variety of conformational characteristics such as occurrence of cis peptide units, flexibility of peptide dimension and variety in hydrogen bonding. The different possible conformations of cyclic triand hexa-peptides are given and certain specific conformational features are discussed for cyclic tetra and pentapeptides. For higher cyclic peptides, the hydrogen bonding requirement for stability of the backbone of the ring, is seen to be kept to a minimum. These various features and their significance are examined and discussed in the light of energy minimization studies and analysis of available experimental data.

Relationship between physiological energy expenditure and biomechanical patterns associated with erect standing.

The deviation of the static weight-bearing patterns under the feet of a lower extremity handicapped person may be measured quantitatively in terms of the Static Weight- Bearing Index. This paper describes the correlation between this index and the physiological energy expenditure associated with the erect standing posture. The Static Weight-Bearing Index can be conveniently used for evaluation of the functional status of the human lower extremity system in stance in case of lower extremity disabled persons who maintain basic weight-bearing mode involving both the limbs in double support condition.

Metal binding to pyridoxal derivatives. An NMR study of the interaction of Eu(III) with pyridoxal phosphate and pyridoxamine phosphate.

The solution conformations of pyridoxal-5'-phosphate and pyridoxamine- 5'-phosphate have been investigated using Eu(III) as a nuclear magnetic resonance shift probe. Binding of Eu(III) to pyridoxal phosphate results in the formation of two complexes, at the phosphate group and the o-hydroxy-aldehyde moiety, which are in slow exchange on the nuclear magnetic resonance time-scale. The lanthanide-induced pseudo contact shifts calculated using the McConnell-Robertson equation (J. Chem. Soc. (1950), 22, 1561) are in good agreement with the experimentally observed values for both pyridoxal phosphate and pyridoxamine phosphate and lead to a family of closely related conformations.