Synthesis and X-ray study of the 6-(N-pyrrolyl)purine and thymine derivatives of 1-aminocyclopropane-1-carboxylic acid

Helical screw-sense preferences of peptides based on chiral, Cα-tetrasubstituted α-amino acids

The preferred helical screw senses of chiral α-amino acids with a C(α)-tetrasubstituted α-carbon atom, as determined in the crystal state by X-ray diffraction analyses on derivatives and peptides, are reviewed. This survey covers C(α)-methylated and C(α)-ethylated α-amino acids, as well as α-amino acids cyclized on the α-carbon, including those characterized by the combination of lack of chirality at the α-carbon with either side-chain or axial chirality. Although, in general, chiral C(α)-tetrasubstituted α-amino acids show a less pronounced bias toward a single helical screw sense than their proteinogenic (C(α)-trisubstituted) counterparts, our analysis highlights significant differences in terms of magnitude and direction of such a bias among the various sub-families of residues, and between individual amino acids within each sub-family as well. The experimental findings can be rationalized, at least in part, on the basis of steric considerations.

Selective anti-tubercular purines: Synthesis and chemotherapeutic properties of 6-aryl- and 6-heteroaryl-9-benzylpurines

6-Aryl- and 6-heteroaryl-9-benzylpurines have been synthesized employing palladium-catalyzed coupling reactions in the step forming the C-C or C-N bond between the aryl- or heteroaryl and the purine. The compounds were screened for activity against Mycobacterium tuberculosis as well as representative Gram+ and Gram- bacteria, and for cytotoxic effects on mammalian cells. Several potent antimycobacterials were identified. These compounds probably act by a novel and selective mechanism; they exhibit low toxicity toward other bacteria as well as mammalian cells.