5-HT(6) receptor modulators: a patent update. Part 2. Diversity in heterocyclic scaffolds.

INTRODUCTION: Among a variety of proteins included in a relatively wide GPCR family, serotonin 5-HT receptors (5-HT(6)Rs) are highly attractive as important biological targets with enormous clinical importance. Among this sub-class, 5-HT(6)R is the most recently discovered group. Available biological data clearly indicate that 5-HT(6)R antagonists can be used as effective regulators in a variety of contexts, including memory formation, age-related cognitive impairments and memory deficits associated with conditions such as schizophrenia, Parkinson's disease (PD) and Alzheimer's disease (AD). Therefore, this receptor has already attracted a considerable attention within the scientific community, due to its versatile therapeutic potential. AREAS COVERED: The current paper is an update to the comprehensive review article published previously in Expert Opinion on Therapeutic Patents [1] Ivashchenko AV, Ivanenkov YA, Tkachenko SE. 5-Hydroxytryptamine subtype 6 receptor modulators: a patent survey. Expert Opin. Ther. Pat, 2010, 20, 1171-1196. Here, the authors mainly focus on small-molecule compounds - 5-HT(6) antagonists - which have been described in recent patent literature, since the end of 2009. To obtain a clear understanding of the situation and dynamic development within the field of 5-HT(6) ligands, having an obvious pharmaceutical potential in terms of related patents, the authors provide a comprehensive search through several key patent collections. They describe the reported heterocyclic compounds with no sulfonyl moiety in sufficient detail to provide a valuable insight in the 5-HT(6)R chemistry and pharmacology. Most of the described compounds are currently classified as multimodal agents with high affinity toward 5-HT(6)R. EXPERT OPINION: Recent progress in the understanding of the 5-HT(6) receptor function and structure includes a suggested constitutive activity for the receptor, development of a number of multimodal small-molecule ligands and re-classification of many selective antagonists as pseudo-selective agents. Several heterocylic structures with or without any basic center provide sufficient supramolecular interactions and show high agonistic/antagonistic activity against 5-HT(6)R. Many 'multitarget' drugs acting, for instance, against several isoforms of 5-HTR, including 5-HT(6)R subtype, as well as against dopamine and/or histamine receptors were shown to have beneficial therapeutic effects. At the same time, these 'unselective' compounds may also increase the side-effect potential. The ensemble of antagonistic activity against 5-HT(6)R and inhibition potency against BuChE can be regarded as the most promising basis for the development of effective drugs with a sufficient therapeutic window for the treatment of several neurodegenerative diseases, including AD and PD.

Kohonen maps for prediction of binding to human cytochrome P450 3A4.

The drug development process utilizes the parallel assessment of activity at a therapeutic target as well as absorption, distribution, metabolism, excretion, and toxicity properties of molecules. The development of novel, reliable, and inexpensive computational methods for the early assessment of metabolism and toxicity is becoming increasingly an important part of this process. We have used a computational approach for the assessment of drugs and drug-like compounds which bind to the cytochromes P450 (P450s) with experimentally determined Km values. The physicochemical properties of these compounds were calculated using molecular descriptor software and then analyzed using Kohonen self-organizing maps. This approach was applied to generate a P450-specific classification of nearly 500 drug compounds. We observed statistically significant differences in the molecular properties of low Km molecules for various P450s and suggest a relationship between 33 of these compounds and their CYP3A4-inhibitory activity. A test set of additional CYP3A4 inhibitors was used, and 13 of 15 of these molecules were colocated in the regions of low Km values. This computational approach represents a novel method for use in the generation of metabolism models, enabling the scoring of libraries of compounds for their Km values to numerous P450s.

In silico estimation of DMSO solubility of organic compounds for bioscreening.

Solubility of organic compounds in DMSO is an important issue for commercial and academic organizations handling large compound collections or performing biological screening. In particular, solubility data are critical for the optimization of storage conditions and for the selection of compounds for bioscreening compatible with the assay protocol. Solubility is largely determined by the solvation energy and the crystal disruption energy, and these molecular phenomena should be assessed in structure-solubility correlation studies. The authors summarize our long-term experimental observations and theoretical studies of physicochemical determinants of DMSO solubility of organic substances. They compiled a comprehensive reference database of proprietary data on compound solubility (55,277 compounds with good DMSO solubility and 10,223 compounds with poor DMSO solubility), calculated specific molecular descriptors (topological, electromagnetic, charge, and lipophilicity parameters), and applied an advanced machine-learning approach for training neural networks to address the solubility. Both supervised (feed-forward, back-propagated neural networks) and unsupervised (Kohonen neural networks) learning methods were used. The resulting neural network models were validated by successfully predicting DMSO solubility of compounds in independent test selections.

Structure-based versus property-based approaches in the design of G-protein-coupled receptor-targeted libraries.

In this work, two alternative approaches to the design of small-molecule libraries targeted for several G-protein-coupled receptor (GPCR) classes were explored. The first approach relies on the selection of structural analogues of known active compounds using a substructural similarity method. The second approach, based on an artificial neural network classification procedure, searches for compounds that possess physicochemical properties typical of the GPCR-specific agents. As a reference base, 3365 GPCR-active agents belonging to nine different GPCR classes were used. General rules were developed which enabled us to assess possible areas where both approaches would be useful. The predictability of the neural network algorithm based on 14 physicochemical descriptors was found to exceed the predictability of the similarity-based approach. The structural diversity of high-scored subsets obtained with the neural network-based method exceeded the diversity obtained with the similarity-based approach. In addition, the descriptor distributions of the compounds selected by the neural network algorithm more closely approximate the corresponding distributions of the real, active compounds than did those selected using the alternative method.

Advanced exact structure searching in large databases of chemical compounds.

Efficient recognition of tautomeric compound forms in large corporate or commercially available compound databases is a difficult and labor intensive task. Our data indicate that up to 0.5% of commercially available compound collections for bioscreening contain tautomers. Though in the large registry databases, such as Beilstein and CAS, the tautomers are found in an automated fashion using high-performance computational technologies, their real-time recognition in the nonregistry corporate databases, as a rule, remains problematic. We have developed an effective algorithm for tautomer searching based on the proprietary chemoinformatics platform. This algorithm reduces the compound to a canonical structure. This feature enables rapid, automated computer searching of most of the known tautomeric transformations that occur in databases of organic compounds. Another useful extension of this methodology is related to the ability to effectively search for different forms of compounds that contain ionic and semipolar bonds. The computations are performed in the Windows environment on a standard personal computer, a very useful feature. The practical application of the proposed methodology is illustrated by several examples of successful recovery of tautomers and different forms of ionic compounds from real commercially available nonregistry databases.

Classification scheme for the design of serine protease targeted compound libraries.

The development of a scoring scheme for the classification of molecules into serine protease (SP) actives and inactives is described. The method employed a set of pre-selected descriptors for encoding the molecular structures, and a trained neural network for classifying the molecules. The molecular requirements were profiled and validated by using available databases of SP- and non-SP-active agents [1,439 diverse SP-active molecules, and 5,131 diverse non-SP-active molecules from the Ensemble Database (Prous Science, 2002)] and Sensitivity Analysis. The method enables an efficient qualification or disqualification of a molecule as a potential serine protease ligand. It represents a useful tool for constraining the size of virtual libraries that will help accelerate the development of new serine protease active drugs.