Biomedical subjects
K Ramnarayan
Publications and source records attributed to K Ramnarayan.
A case of histoplasma posthitis.
The present report describes a case of disseminated histoplasmosis with involvement of the prepuce. Phimosis resulting from histoplasma posthitis is exceedingly rare and hence being documented.
Pseudomonas maltophilia endocarditis.
Explore the source record for details and available documents.
Conformational studies on beta-amino acid-containing peptides. I.
Modified amino acids (such as beta-amino acids) are becoming increasingly popular research tools in the development of orally active and metabolically stable peptidomimetics. We present conformational energy calculations using molecular mechanics (MM2) on two model compounds containing beta-amino acids. The low-energy models are characterized by a lack of intramolecular hydrogen-bonding interactions, qualitatively consistent with the results of the IR studies. The structures obtained from the limited amount of x-ray crystal data on compounds with beta-amino acid incorporated lie within 3 kcal/mol of the global minimum obtained from the present calculations. Preliminary stereochemical guidelines for the incorporation of beta-amino acid residues have been proposed.
Fixed eruption due to rifampicin.
Cutaneous side effects due to Rifampicin are rare (less than 5%). We report an urticarial type of fixed eruption due to Rifampicin. Fixed eruption due to Rifampicin is not reported earlier.
Membranous septal aneurysm following V.S.D. closure.
Explore the source record for details and available documents.
Conformational studies on model peptides with 1-aminocyclobutane 1-carboxylic acid residues.
Conformationally constrained peptidomimetics are being increasingly used in the development of 3-D pharmacophores of peptide-based drug candidates and to alter their metabolic stability towards achievements of oral bioavailability. Here we present conformational energy calculations on model compounds containing 1-aminocyclobutane carboxylic acid (ACBC) and its derivatives using molecular mechanics methods. The low-energy models adopt conformations characteristic of a variety of regular structures such as the alpha-helix, 3(10)-helix, gamma-turn and polyproline-II-type three- and fourfold helices. The energetically most favored models adopt the gamma-turn (2.2(7) helix) conformation or alpha-/3(10)-helical conformation, both of either handedness, depending on the substituents on the cyclobutane. These results are qualitatively consistent with the crystal structures of peptide analogs containing ACBC and have implications for the design of peptidomimetics.
Characterization of a linear pentapeptide containing two consecutive beta-turns.
The contiguous occurrence of two beta-turns is examined using molecular mechanics calculations. A tripeptide can take up special conformations known as beta-turns resulting in the reversal of the chain. There are two major classes of beta-turns, called type I beta-turn and type II beta-turn. In the specific case described here, the third peptide unit forms a part of a second turn resulting in the formation of a two-turn motif. In the case of dihydropteridine reductase, this motif is involved in cofactor binding. This study examines the energetic and conformational preferences for chain-reversed motifs. Energy minimizations were carried out on models of pentapeptides with four different sequences for residues 2 through 5: (i) GGGG, (ii) AGGA, (iii) AGAG and (iv) AAAA. For each of the above sequences, all four possible combinations of type I and type II beta-turns were considered. Out of the four possible combinations, the (II, II) combination is the most planar one. The (I, I) combination is the least planar. For the all-Gly model and the all-Ala model, the most favored conformation energetically is a type I-type I combination. On the other hand, the sequence AGGA favors a type II-type I combination, and the sequence AGAG prefers a type II-type II combination. A computer search for double-turn motifs at the Brook-haven Protein Data Bank revealed that the (I, I) combination occurs with the highest frequency, and the (I, II) combination has the next highest frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
Conformational studies on model peptides with 1-aminocyclopropane 1-carboxylic acid residues.
The design of metabolically stable, conformationally constrained peptidomimetics is an increasingly used approach in developing orally active drug candidates in pharmaceutical research. In this paper we present conformational energy calculations on model compounds containing 1-aminocyclopropane carboxylic acid (ACC) and its derivatives using molecular mechanics methods. The low energy models adopt conformations characteristic of a variety of regular structures such as the alpha-helix, gamma-turn and three- and fourfold helices. The energetically most favored models adopt either the left- or right-handed 2.2(7) helical conformation or the gamma-turn. These results are qualitatively consistent with the crystal structures of peptide analogs containing ACC and have potential implications for the design of peptidomimetics where the conformational features characteristic of a specific type of gamma-turn are desired.