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.
Chemical Releasers of Social Behaviour - VI. The Relation of Structure to Activity of Ketones as Releasers of Alarm for Iridomyrmex pruinosus (Roger)
Abstract 2-Heptanone, the alarm pheromone produced by Iridomyrmex pruinosus, is a powerful attractant for workers of this dolichoderine species. I. pruinosus also appears to employ this alarm pheromone for defense. The possible origin of alarm pheromones from defensive secretions is discussed. The abilities of 49 ketones to produce typical alarm behaviour in I. pruinosus were determined in order to establish the relationship between chemical structure and alarm-releasing activity. Ketones in the range C3 to C13 were tested on both laboratory and strong field colonies. In the series of 2-alkanones, activity was present in the C5 to C10 ketones, the most pronounced activity occurring in the range C6 to C9. The corresponding cycloalkanones showed no activity. In general, movement of the carbonyl group toward the centre of the hydrocarbon chain caused at least a slight diminution in activity. The introduction of a second carbonyl group either had no effect or produced a slight drop in the ability of the compound to release alarm. Unsaturation in the aliphatic chain either slightly increased or did not alter the activity of the synthetic pheromones. Branched methyl groups produced compounds which were generally less active than their unbranched isomeric counterparts, although this relationship was not absolute, especially in the C7 to C9 ketones. Activity was also present in some phenyl alkyl ketones, which suggests that the aromatic ring can correspond to an aliphatic portion of an alkanone. These results are discussed in terms of the absolute structural requirements of a maximally active alarm pheromone for I. pruinosus. The data demonstrate that alarm releasers, in common with other types of pheromones, require a degree of structural specificity in order to manifest maximum activity.