Structure-activity relationships in sweeteners. I. Nitroanilines, sulphamates, oximes, isocoumarins and dipeptides

Besides the hydrophilic AH-B moiety in sweeteners, the morehydrophobic ‘third binding sites’ play an essentialrole in inducing sweetness. The distances between these molecularfunctions seem to be very critical, but exact data are lacking.To describe stereochemical requirements more precisely, newconceptual parameters were introduced, namely , and (minimum,optimum and maximum distances between these third binding sitesand the atoms A, H and B of the AH-B moieties respectively,especially appropriate for homologous series) and the S value(shortest distance between the position of an atom and the planeformed by the atoms A, H and B of the AH-B moiety). The dimensionsof the relevant side chains of five homologous series of sweeteners– sulphamates, oximes, nitroanilines, isocoumarins anddipeptides — were determined. We calculated that the positionsof the , and parameters with regard to the AH-B moieties arelocated around two main axes forming 95? angles with the H-Baxis in the AH-B moieties for sulphamates and isocoumarins and125? angles for oximes, nitroanilines and dipeptides. The positionsof are, for all potent sweeteners, situated at 70—85%of the maximum distance of viewed from the centre of the Aatom, while for , this value was found to be 15% for oximes,25% for nitroanilines, 40% for sulphamates, 50—70% fordipeptides and 65% for isocoumarins. The results indicate thereare at least three — but a maximum of four — differentreceptor sites. They have very narrow site clefts with maximumheights of -0.6 nm.     

Structure-activity relationships of urotensin II and URP

Urotensin II (U-II) and urotensin II-related peptide (URP) are the endogenous ligands for the orphan G-protein-coupled receptor GPR14 now renamed UT. At the periphery, U-II and/or URP exert a wide range of biological effects on cardiovascular tissues, airway smooth muscles, kidney and endocrine glands, while central administration of U-II elicits various behavioral and cardiovascular responses. There is also evidence that U-II and/or URP may be involved in a number of pathological conditions including heart failure, atherosclerosis, renal dysfunction and diabetes. Because of the potential involvement of the urotensinergic system in various physiopathological processes, there is need for the rational design of potent and selective ligands for the UT receptor. Structure-activity relationship studies have shown that the minimal sequence required to retain full biological activity is the conserved U-II(4-11) domain, in particular the Cys5 and Cys10 residues involved in the disulfide bridge, and the Phe6, Lys8 and Tyr9 residues. Free alpha-amino group and C-terminal COOH group are not necessary for the biological activity, and modifications of these radicals may even increase the stability of the analogs. Punctual substitution of native amino acids, notably Phe6 and Trp7, by particular residues generates analogs with antagonistic properties. These studies, which provide crucial information regarding the structural and conformational requirements for ligand-receptor interactions, will be of considerable importance for the design of novel UT ligands with increased selectivity, potency and stability, that may eventually lead to the development of innovative drugs.     

Polycations as prostaglandin synthesis inducers. II. Structure-activity relationships

Moderately high molecular weight polycations stimulate arachidonic acid release with concomitant synthesis and release of prostaglandins in cultured 3T3 mouse fibroblasts. We have examined a series of synthetic polycations for prostaglandin synthesis-inducing activity as an approach to defining the structural features required for activity. Extensive (greater than 80%) acetylation of poly(vinylamine) was tolerated without loss of activity, indicating that a uniform high density of charges is not required. However, complete acetylation of poly(vinylamine) abolished activity, indicating that some positive charges are required for activity. full activity was observed for charge densities in the range of one per two to one per six atoms of polymer backbone. Branched and linear polycations activated equally well. Location of the charge with respect to the polymer backbone did not affect activity in polymers bearing charges located up to seven atoms away from the backbone. Polycations lacking primary or secondary amino groups exhibited full activity, indicating that Schiff base formation is not required for activity. These results are consistent with a model in which activation involves electrostatic interactions with discrete anionic sites on the target cell.     

Structure-activity relationships in the development of hypoxic cell radiosensitizers. II. Cytotoxicity and therapeutic ratio.

This paper describes measurements of the aerobic cytotoxicity of 42 nitroaromatic and nitroheterocyclic compounds towards Chinese Hamster cells in vitro. The results of acute and chronic exposure were quantified, and the concentration C required to achieve a standard response estimated. Fitting the data to an equation of the form - log C = b0 + b1E, where E is the one-electron reduction potential, explained 47 and 71 per cent of the variance in the acute and chronic aerobic cytotoxicity respectively. The addition of further terms to the equation, quantifying partition properties, was not statistically significant. The coefficient b1 was similar for both acute and chronic exposure; the dependence of both cytotoxicity and radiosensitization efficiency on reduction potential was also similar. A therapeutic ratio derived from these in vitro measurements showed no dependence on redox or partition properties. The insensitivity of cytotoxicity and radiosensitization properties to variations in molecular structure, other than those which influence redox behaviour, offers exceptional flexibility in developing compounds of improved therapeutic ratio.     

Structure-activity relationships of aromatic diamines in the Ames Salmonella typhimurium assay. Part II.

Structure-activity relationships in the case of aromatic monoamines, diversely substituted on the ring, using the mutagenic activity in the Ames test were studied in part I. This part II is based on the same general principles but applied to phenylene diamines (ortho, para and meta) diversely substituted on the ring.     

Structure-activity relationships in nitrothiophenes

The structure and electronic properties of a series of biologically active 2-nitrothiophenes (1) have been calculated using both semi-empirical and ab initio molecular orbital methods. Multi-linear regression analysis suggests that there is a reasonable correlation between the experimental activity of the derivatives against either Escherichia coli or Micrococcus luteus and calculated properties such as the HOMO energies, the total atomic charges and ring angles at the heterocyclic sulfur atom, but there is no correlation with the calculated solvation energies or dipole moments. The presence or absence of an additional nitro group at the 3-position of the ring also has a significant effect on the activity. From the derived QSAR equations, the 2-chloro- or 2-bromo-3,5-dinitrothiophenes (1a and 1c) are predicted to show the highest activity against both bacteria, while 2-nitrothiophene (1n) is predicted to be the least active, in line with the experimental results.     

Structure-activity relationships of anandamide, an endogenous cannabinoid ligand.

Identification of arachidonylethanolamide (anandamide) as an endogenous cannabinoid is one of the most important developments in cannabinoid research in recent years. In a relatively short period of time thereafter, pharmacological and biochemical studies have confirmed initial speculations that anandamide is a neuromodulator and significantly advanced our understanding of cannabinoid biochemistry. Moreover, the discovery of anandamide has led to the identification of two heretofore unknown proteins associated with cannabinoid physiology: 1) Anandamide Amidohydrolase (AAH), an enzyme responsible for the hydrolytic breakdown of anandamide and 2) the Anandamide Transporter (ANT), a carrier protein involved in the transport of anandamide across the cell membrane. Evidence obtained so far suggests that these two proteins, in combination, are responsible for the termination of the biological actions of anandamide. Also, the discovery of anandamide has revealed a novel class of more selective cannabimimetic agents possessing a somewhat different pharmacological profile of potential therapeutic value. A number of such analogs have now been reported many of which possess markedly improved cannabinoid receptor affinity and metabolic stability compared to those of the parent ligand. Generally, anandamide and all known analogs exhibit significant selectivity for the CB1 receptor and modest to very low affinity for CB2. For this reason, this group of compounds can be considered as CB1 ligands. The purpose of this review is to summarize the structure-activity relationships (SAR) of anandamide for the CB1 cannabinoid receptor and to define the structural requirements for the substrates and the inhibitors of anandamide amidohydrolase and the anandamide transporter.     

Structure-activity relationships of the azide metabolite, azidoalanine, in S. typhimurium

Azide is metabolized to the proximate mutagen, L-azidoalanine in bacterial systems. While this novel mutagenic metabolite plays a key role in azide mutagenesis, the biochemistry of this role is unknown. The chemical synthesis of authentic racemic azidoalanine and several derivatives thereof allowed the exploration of structure-activity relationships with this unique mutagen. We found that whereas azide, azidoalanine and azidoalanine tert.-butyl ester were of comparable mutagenic potency, derivatives which lack the free amino group, such as azidopropionic acid and amino-blocked azidoalanine, were orders of magnitude less active. These findings demonstrate that the free amino group is essential for significant activity, while the carboxyl group may be less important. This conclusion together with the finding that DL-azidoalanine is a less potent mutagen than azide itself, suggests that the metabolite, while necessary for azide mutagenicity, may not be the ultimate mutagenic species. Instead, the data are consistent with the hypothesis that azidoalanine requires further bioactivation.     

Structure-activity relationships of synthetic diosgenyl diglycosides.

The haemolytic and antifungal activities of six synthetic diosgenyl diglycosides and diosgenyl maltotrioside were compared with each other and with those of the parent glucoside. In general, the haemolytic activity of each of these glycosides was higher than, and the antifungal activity as strong as, that of the glucoside. However, both activities of the lactoside were much lower than those of the others.     

Structure-activity relationships in beta-defensin peptides

The beta-defensins comprise a large family of small cationic antimicrobial peptides widely distributed in plants, mammals and insects. These cysteine rich peptides display multifunctional properties with implications as potential therapeutic agents. Recent research has highlighted their role in both the innate and adaptive immune systems as well as being novel melanocortin ligands. Studies investigating structure and function provide an insight into the molecular basis of their immunological properties.     

DNA intercalation and inhibition of topoisomerase II. Structure-activity relationships for a series of amiloride analogs

Among its many properties, amiloride is a DNA intercalator and topoisomerase II inhibitor. Previous work has indicated that the most stable conformation for amiloride is a planar, hydrogen-bonded, tricyclic structure. To determine whether the ability of amiloride to intercalate into DNA and to inhibit DNA topoisomerase II was dependent on the ability to assume a cyclized conformation, we studied the structure-activity relationship for 12 amiloride analogs. These analogs contained structural modifications which could be expected to allow or impede formation of a cyclized conformation. Empirical assays consisting of biophysical, biochemical, and cell biological approaches, as well as computational molecular modeling approaches, were used to determine conformational properties for these molecules, and to determine whether they intercalated into DNA and inhibited topoisomerase II. Specifically, we measured the ability of these compounds to 1) alter the thermal denaturation profile of DNA, 2) modify the hydrodynamic behavior of DNA, 3) inhibit the catalytic activity of purified DNA topoisomerase II in vitro, 4) promote the topoisomerase II-dependent cleavage of DNA, and 5) inhibit functions associated with DNA topoisomerase II in intact cells. Results indicated that only those analogs capable of cyclization could intercalate into DNA and inhibit topoisomerase II. Thus, the ability of amiloride and the 12 analogs studied to intercalate into DNA and to inhibit topoisomerase II appears dependent on the ability to exist in a planar, hydrogen-bonded, tricyclic conformation.     

Repressor--operator interaction in the lac operon. II. Observations at the tyrosines and tryptophans

This paper shows that ¹⁹F-nuelear magnetic resonance spectroscopy on 3-fluoro-tyrosine and 5-fluorotryptophan-substituted wild-type lactose operon repressors from Escherichia coli can be used to examine the interactions with lac operator DNA.A survey of inducer and salt concentration effects on the repressor-operator complex is presented. The data lead us to a scheme for the interactions between the repressor, operator and inducer, in both binary and ternary complexes, that accommodate the results published by others.The complex between the tetrameric repressor and one 36 base-pair operator DNA fragment results in the simultaneous broadening of the resonances from all four N-terminal DNA binding domains. The actual contacts made by these binding domains are similar but probably not identical.The binding of the inducer molecule to the tetrameric repressor results in an allosteric change that can be monitored by the increased intensity of the resonances from individual tyrosine residues in the N-terminal binding domain. This increased N-terminal tyrosine resonance intensity in the complex is transmitted to repressor subunits that have not yet bound an inducer molecule.     

Structure-activity relationships in coeliac-toxic gliadin peptides

Summary. Computer modelling studies of two groups of biologically-active peptides derived from A-gliadin indicated that the most likely structures were α-helical ones, in the case of serine-containing peptides, and random peptides coil types featuring β-turns, in the case of proline-rich, tyrosine-containing peptides. The serine-containing group of peptides appear to be essentially cytotoxic in animal models of coeliac disease, whilst the tyrosine-containing group have the capacity to initiate damaging immunological reactions in patients with coeliac disease. Both types of activity in coeliac disease are only possible if there is defective digestion of the active peptides, as mucosal digestion studies indicate. In the case of the serine-containing peptides, activity of the peptides is linked to the presence of PSQQ and also probably QQQP motifs. With the tyrosine-containing peptides, sequences such as QQPY and/or QPYP are associated with immunological activity and hence toxicity. Received November 8, 2000 Accepted December 11, 2000