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Biomedical subjects

K Ramnarayan

Publications and source records attributed to K Ramnarayan.

36 records · Page 2Linked to original sources
PubMed1985

Peripheral ameloblastoma.

The clinical presentation and histological features of peripheral ameloblastoma, occurring on the floor of the mouth in a 65-year-old male, are described. The lesion was surgically excised. All the classical features of peripheral ameloblastoma were seen in this patient.

Aged↗
PubMed1984

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.

Adult↗
PubMedDate not supplied

Toward designing drug-like libraries: a novel computational approach for prediction of drug feasibility of compounds.

Prediction of the degree of drug-like character in small molecules is of great industrial interest. The major barrier, however, is the lack of a definition for drug-like character. We used the concept of the multilevel chemical compatibility (MLCC) between a compound and a drug library as a measure of the drug-like character of a compound. The rationale is that the local chemical environment of each atom or group of atoms in a compound largely contributes to the stability, toxicity, and metabolism in vivo. A systematic comparison of the local environments within a compound and those within the existing drugs provides a basis for determining whether and how much a compound is drug-like. We applied the MLCC calculations to four test sets: top selling drugs, compounds under biological testing prior to the preclinical test, anticancer drugs, and compounds known to have poor drug-like character. The following conclusions were obtained: (1) A convergent number of unique local structure types were found in the analysis of the library of the existing drugs. It suggests that the current drug library contains about 80% of all the viable types; therefore, discovery of a drug with new local structures is only an event of relatively small probability. (2) The method is highly selective in discerning drug-like compounds: most of the top drugs are predicted to be drug-like, about one-quarter of the biological testing compounds are drug-like, and about one-fifth of the anticancer drugs are drug-like. (3) The method also correctly predicted that none of the known problematic compounds are drug-like. (4) The method is fast enough for computational screening of virtual combinatorial chemistry libraries and databases of available compounds.

Combinatorial Chemistry Techniques↗
PubMedDate not supplied

Quadruple therapy for initial eradication of Helicobacter pylori in peptic ulcer: comparison with triple therapy.

BACKGROUND: Quadruple therapy appears to be more effective than standard triple therapy in the management of patients with Helicobacter pylori infection who harbor drug-resistant organisms. No data are available on the relative efficacies of triple and quadruple drug regimens from India. METHODS: Consecutive patients with peptic ulcer and H. pylori infection were randomized to receive lansoprazole 30 mg twice daily along with either amoxycillin (500 mg four times daily) and clarithromycin (500 mg twice a day) (Group A), or tri-potassium dicitrato bismuthate (120 mg four times daily), metronidazole (400 mg thrice daily) and tetracycline (500 mg 4 times daily) (Group B) for 10 days. Presence of H. pylori infection was looked for using an in-house urease test and histology before starting treatment, and 30 days after completion of treatment. RESULTS: Twenty-nine of 35 patients in Group A and 24 of 33 in Group B had eradication of infection (82.8% and 72.7% by intention-to-treat analysis, and 87.9% and 85.7% by per protocol analysis, respectively; p = ns). Side-effects occurred in 4 (12%) and 5 (18%) patients in Groups A and B, respectively (p = ns); discontinuation of drugs was required in two patients in group B. CONCLUSIONS: Quadruple therapy for initial treatment of H. pylori infection does not offer any advantage over standard triple therapy in Indian patients.

Adolescent↗
PubMedDate not supplied

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.

Amino Acids↗
PubMedDate not supplied

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.

Adolescent↗
PubMedDate not supplied

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.

Amino Acids↗
PubMedDate not supplied

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)

Amino Acid Sequence↗
PubMedDate not supplied

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.

Amino Acids↗