Intermolecular association and geometrical shape as two factors controlling chemical reactions
BIOLOGICAL phenomena are highly specific1–4 and much effort has been devoted to establishing the relationship between biological activity and molecular shape. We report here the sharp dependence of selectivity in the oxidation of a pair of thiols on their structures or on environment, the mode of each dependence of selectivity being controlled dominantly by their tendency towards intermolecular association.
Structure and conformation of a novel inhibitor of angiotensin I converting enzyme--a tripeptide containing phosphonic acid.
A novel phosphotripeptide, (IR)-1-(N-(N-acetyl-L-isoleucyl)-L-tyrosyl)amino-2-(4-hydroxyphenyl)ethy l- phosphonic acid, is a potent inhibitor of angiotensin I converting enzyme (ACE). ACE inhibitory activity in vitro of the peptide is comparable to that of captopril. Its diethylester (C29H42N3O8P, molecular weight, 591.6) crystallizes in the monoclinic space group C2, with cell constants: a = 25.666(9), b = 9.590(8), c = 13.557(2)A, beta = 91.65(2) degrees, Z = 4, Dc = 1.17 g/cm3. The structure was solved by MULTAN 11/82 and refined by full matrix least-squares methods to a final R-factor of 0.063 for 2123 unique reflections (F greater than 3 sigma(F] measured on an Enraf-Nonius CAD-4 diffractometer (CuK alpha, lambda = 1.541 8 A, T = 295 K). The absolute configuration of the alpha-carbon where the phosphonic acid is attached was determined unequivocally by referring to the L-isoleucyl moiety whose absolute configuration is known. The conformation of the molecule is relatively rigid owing to the intramolecular requisites and the resultant relative disposition of hetero atoms, which are necessary to its biological activities, are confined to the corresponding disposition in captopril.
One-pot synthesis of annulated pyrido[2,3-d:6,5-d]dipyrimidine derivatives using nitrogen based DBU catalyst in aqueous ethanol medium
Abstract We have reported DBU as an efficient organocatalyst for one-pot three-component synthesis of annulated pyrido[2,3- d :6,5- d ]dipyrimidine derivatives using aromatic aldehyde, thio-barbituric acid and 6-amino-uracil in aqueous ethanol under reflux. The attractive advantages of this process are mild reaction conditions, environment friendly procedure, short reaction times, easy isolation of products, and excellent yields (72–89%).