Orbital symmetry in QSAR: some Schiff's base inhibitors of carbonic anhydrase.

In a reexamination of some data on the inhibition of carbonic anhydrase (CA) isozymes I and II by some phenyl and pyridyl substituted sulfanilamide Schiff's bases we have found that activity can better be explained by considering the directions of the nodes in pi-like near frontier orbitals in the molecules. The near-frontier orbitals involved are those that are analogous to the degenerate pairs of HOMO and LUMO orbitals of benzene. This effect seems common in compounds which contain variously substituted benzene rings and is probably critical to understanding the activity of any aromatic molecule which is bound to its receptor by pi-pi charge transfer interactions.

Protease inhibitors, part 13: Specific, weakly basic thrombin inhibitors incorporating sulfonyl dicyandiamide moieties in their structure.

A series of compounds has been prepared by reaction of dicyandiamide with alkyl/arylsulfonyl halides as well as arylsulfonylisocyanates to locate a lead for obtaining weakly basic thrombin inhibitors with sulfonyldicyandiamide moieties as the S1 anchoring group. The detected lead was sulfanilyl-dicyandiamide (K1 of 3 microM against thrombin, and 15 microM against trypsin), which has been further derivatized at the 4-amino group by incorporating arylsulfonylureido as well as amino acyl/dipeptidyl groups protected at the amino terminal moiety with benzyloxycarbonyl or tosylureido moieties. The best compound obtained (ts-D-Phe-Pro-sulfanilyl-dicyandiamide) showed inhibition constants of 9 nM against thrombin and 1400 nM against trypsin. pKa measurements showed that the new derivatives reported here do indeed possess a reduced basicity, with the pKa of the modified guanidine moieties in the range 7.9-8.3 pKa units. Molecular mechanics calculations showed that the preferred tautomeric form of these compounds is of the type ArSO2N=C(NH2) NH-CN, probably allowing for the formation of favorable interaction between this new anchoring group and the active site amino acid residue Asp 189, critical for substrate/inhibitor binding to this type of serine protease. Thus, the main finding of the present paper is that the sulfonyldicyandiamide group may constitute an interesting alternative for obtaining weakly basic, potent thrombin inhibitors, which bind with less affinity to trypsin.

Protease inhibitors: synthesis of a series of bacterial collagenase inhibitors of the sulfonyl amino acyl hydroxamate type.

A series of sulfonyl amino acyl hydroxamates incorporating alkyl/arylsulfonyl-N-2-nitrobenzyl-L-alanine was prepared. Related compounds were obtained by reaction of N-2-nitrobenzyl-L-Ala with aryl isocyanates, arylsulfonyl isocyanates, or benzoyl isothiocyanate, followed by the conversion of the COOH into the CONHOH moiety. The new compounds were assayed as inhibitors of the Clostridium histolyticum collagenase (ChC), a bacterial protease involved in the degradation of extracellular matrix. Many of the obtained hydroxamates proved to be effective bacterial collagenase inhibitors, the main contributor to activity being the substitution pattern at the sulfonamido moiety. The best ChC inhibitors were those containing pentafluorophenylsulfonyl and 3- and 4-protected-aminophenylsulfonyl P(1)(') groups among others, with affinities in the low nanomolar range. This study also proves that the 2-nitrobenzyl- moiety, similarly to the 4-nitrobenyl one previously investigated (Scozzafava, A.; Supuran, C. T. J. Med. Chem. 2000, 43, 1858-1865) is an efficient P(2)(') anchoring moiety for obtaining potent bacterial collagenase inhibitors.

Carbonic anhydrase inhibitors. Part 86. A QSAR study on some sulfonamide drugs which lower intra-ocular pressure, using the ACE non-linear statistical method.

Quantum chemical QSAR expressions have been developed for a heterogeneous group of 36 sulfonamides which have been shown to lower intraocular pressure in in vivo tests on animals. It was found, using the ACE statistical technique, that the lowering of intraocular pressure correlated non-linearly with K(I) for carbonic anhydrase inhibition and with solubility. Non-linear transformations had to be applied to both the response variable and to solubility. Chemical variables found to be relevant to CA inhibition included the dipole moment vector, the frontier orbital energies, the solvation energy determined by the COSMO model, the electrostatic potential based charges on the atoms of the sulfonamide group, and the size and polarizability of the molecule.

Protease inhibitors: synthesis and QSAR study of novel classes of nonbasic thrombin inhibitors incorporating sulfonylguanidine and O-methylsulfonylisourea moieties at P1.

Using benzamidine as a lead molecule, two series of alkyl/aralkyl/arylsulfonylguanidines/sulfonyl-O-methylisoureas+ ++ have been prepared and assayed as inhibitors of two serine proteases, thrombin and trypsin. The study showed that sulfaguanidine and its corresponding O-methylisourea derivative possess moderate but intrinsically selective thrombin inhibitory properties, with K(I)'s around 100 nM against thrombin and 1350-1500 nM against trypsin. Further elaboration of these two molecules afforded compounds that inhibited thrombin with K(I)'s in the range of 12-50 nM, whereas affinity for trypsin remained relatively low. Such compounds were obtained by attaching benzyloxycarbonyl- or 4-toluenesulfonylureido-protected amino acids (such as L- and D-Phe or L-Pro) or dipeptides (such as Phe-Pro, Gly-His, beta-Ala-His, or Pro-Gly) to the two leads mentioned above, sulfaguanidine and 4-aminobenzenesulfonyl-O-methylisourea. Thus, the present study proposes two novel approaches for the preparation of high-affinity, specific thrombin inhibitors: two novel S1 anchoring moieties in the already large family of arginine/amidine-based inhibitors and novel peptidomimetic scaffolds obtained by incorporating tosylureido amino acids in the hydrophobic binding site(s). The first one is important for obtaining bioavailable thrombin inhibitors, devoid of the high basicity of the commonly used arginine/amidine-based inhibitors, whereas the second one may lead to improved water solubility of such compounds due to facilitated metal (sodium) salts formation (at the relatively acidic SO(2)NHCO protons) as well as increased stability at hydrolysis (in vivo). A QSAR study also explained the activity in terms of global properties of the molecules, electronic properties of the sulfonylguanidine/sulfonylisourea moiety, and novel descriptors, the frontier orbital phase angles (FOPA), that account for the directions of the nodes in the pi orbitals in the aromatic portion of those of the drugs in which the sulfonyl group was bound to a benzene ring. For thrombin inhibition, the size of the molecule was the dominant influence, while for trypsin inhibition the FOPA was the principal determinant of activity. The dependence of activity on the FOPA variables is perhaps the clearest example of a quantum effect in pharmacology and suggests a promising new tool for drug design.

Protease inhibitors. Part 2. Weakly basic thrombin inhibitors incorporating sulfonyl-aminoguanidine moieties as S1 anchoring groups: synthesis and structure-activity correlations.

Two series of derivatives have been prepared and assayed as inhibitors of two physiologically relevant serine proteases, human thrombin and human trypsin. The first series includes alkyl-/ aralkyl-/aryl- and hetarylsulfonyl-aminoguanidines. It was thus observed that sulfanilyl-aminoguanidine possesses moderate but intrinsically selective thrombin inhibitory properties, with KI values around 90 and 1400 nM against thrombin and trypsin respectively. Further elaboration of this molecule afforded compounds that inhibited thrombin with KI values in the range 10-50 nM, whereas affinity for trypsin remained relatively low. Such compounds were obtained either by attaching benzyloxycarbonyl- or 4-toluenesulfonylureido-protected amino acids (such as D-Phe, L-Pro) or dipeptides (such as Phe-Pro, Gly His, beta-Ala-His or Pro-Gly) to the N-4 atom of the lead molecule, sulfanilyl-aminoguanidine, or by attaching substituted-pyridinium propylcarboxamido moieties to this lead. Thus, this study brings novel insights regarding a novel non-basic S1 anchoring moiety (i.e., SO2NHNHC(=NH)NH2), and new types of peptidomimetic scaffolds obtained by incorporating tosylureido-amino acids/pyridinium-substituted-GABA moieties in the hydrophobic binding site(s). Structure-activity correlations of the new serine protease inhibitors are also discussed based on a QSAR model described previously for a large series of structurally-related derivatives (Supuran et al. (1999) J. Med. Chem., in press).

The frontier orbital phase angles: novel QSAR descriptors for benzene derivatives, applied to phenylalkylamine hallucinogens.

A new empirical electronic descriptor, obtained from a molecular orbital calculation and applicable to benzene derivatives, is proposed. It is shown that this descriptor, the frontier orbital phase angle, correlates very strongly with the pharmacological activity in humans of a large series of hallucinogenic phenethylamines. In the largest QSAR study on such hallucinogens yet reported, it is demonstrated that the phase of mixing of degenerate frontier orbitals of benzene to form the frontier orbitals of the drug results in the best electronic descriptor yet found for hallucinogenic activity in phenylalkylamines.

Carbonic anhydrase activators. 3: structure-activity correlations for a series of isozyme II activators.

A quantitative structure-activity relationship for some arylalkylamine and arylalkylamino acid activators of carbonic anhydrase, of diverse chemical structure, is presented. A number of descriptors were calculated by the complete neglect of differential overlap (CNDO/2) method, and related to biological activity by regression analysis and partial least squares. Both charge, in the form of the charge of the most highly charged atom in the molecule, and size, in the form of the smallest dimensions of the molecule, are shown to be important descriptors. It is shown that molecules bearing highly charged oxygen or nitrogen atoms tend to have high activity, and that the enzyme can accommodate molecules of only a limited size.

Structure-activity correlations for psychotomimetics. 1. Phenylalkylamines: electronic, volume, and hydrophobicity parameters.

CNDO/2 calculations have been performed on a series of alkyl, alkoxy, and alkylthio derivatives of phenethylamine and phenylisopropylamine. The results of these, of van der Waals volume calculations, and of Hansch type hydrophobicity calculations were correlated with psychotomimetic activity by chemometric methods. Eight parameters, involving seven chemical descriptors, were found to be highly significant. Directional hydrophobicity and volume effects were found, which suggests that steric and hydrophobic interactions in the neighborhood of the receptor site are important. A puzzling but strong interaction effect between meta and para substituents was noted. Electronic terms may be explicable in terms of formation of charge-transfer complexes by accepting, rather than by donating, charge, as has been believed in the past. A charge effect indicates that a charge or dipole is influential at the binding site, or alternatively, a specific reactivity at the meta position is involved.