Clinical candidates

At Merck Research Laboratories, the imidazole ring ia losartan (81, K = n — butyl), a novel clinical candidate against hypertension, was replaced with a pyrazole ring (52). Some of the best compounds are represented by formula (82), where K = n — butyl and R = 2,6-dichlorophenyl, 2-chlorophenyl, or... 

The stmctures of selected cephalosporins on the U.S. market, or in the final stages of development, are shown in Tables 4—8 (see also 78, 87). For every cephalosporin which has made it to the marketplace, HteraHy thousands of analogues were synthesized in order to estabUsh the stmcture-activity profile and allow selection of a clinical candidate. In addition to these compounds, there is a tremendous number of cephalosporin compounds currendy at various stages of development. A more extensive listing of the newer cephalosporins under preclinical or clinical evaluation may be found in a number of reviews (79,88). 

In general, there are three milestones for the drug discovery process. The first is the identification of a verified hit series (primary activity in a related series of molecules), the second the determination of a lead series (series with primary activity and drug-like properties), and the third a clinical candidate (activity, positive pharmaceutical, and pharmacokinetic properties devoid of toxicity). An example... 

Poor pharmacokinetics and toxicity are important causes of costly late-stage failures in drug development. It is generally recognized that, in addition to optimized potency and specificity, chemical libraries should also possess favorable ADME/Tox and druglike properties [77-80]. Assessment of druglike character is an attempt to decipher molecular features that are likely to lead to a successful in vivo and, ultimately, clinical candidate [81-83]. Many of these properties can be predicted before molecules are synthesized, purchased, or even tested in order to improve overall lead and library quality. 

The major successes in treating bacterial infections that were achieved by the antibiotics discovered in the middle part of the last century are now under severe threat from the emergence of resistant strains. Very few new classes of antibacterial have been created in the past 20 years. Peptide deformylase represents a new biochemical target and clinical candidates are beginning to emerge. Chapter 3 reviews progress to date. 

A lead is variously defined in the pharmaceutical industry as a compound derived from a hit with some degree of in vitro optimization (potency in primary assay, activity in functional and/or cellular assay), optimization of physical properties (solubility, permeability), and optimization of in vitro ADME properties (microsomal stability, CYP inhibition). Moreover, a lead must have established SAR/SPR around these parameters such that continued optimization appears possible. A lead may also have preliminary PK and in vivo animal model data. However, it is the task of the lead optimization chemist to improve PK and in vivo activity to the levels needed for identification of a clinical candidate. 

Replacement of the phenyl group of anthranilic acid by a cycloalkene represents another strategy to obtain intellectual property. This endeavor resulted in three consecutive patent applications [73-75] and a publication [76]. The advantages of tetrahydro anthranilic acid as a surrogate for anthranilic acid include reduced CYP2C8 and 2C9 inhibition and improved oral exposure in mice (analogs 25 vs. 12). Ultimately, a pre-clinical candidate, MK-6892 (26), was selected from this series due to its... 

Compound 46 was further developed as a clinical candidate designated MK-0354 [102], which demonstrated robust dose-dependent reduction of plasma FFA in humans over 5h after single doses up to 4000 mg and... 

At least four clinical candidates including GSK-256073 [112], MK-0354 [102], MK-1903 [113], and INCB-19062 [91], and one preclinical candidate MK-6892 [77] have been reported. Neither the structure of GSK-256073, nor the clinical data, has been reported. In Phase II clinical trials, neither GPR109A partial agonist MK-0354, nor the full agonist MK-1903 showed substantial lipoprotein effects, and both candidates were discontinued. INCB-19062 is targeted to a type II diabetes indication based upon the related role of FFA to insulin sensitization in type II diabetes, and the robust FFA lowering effect observed in a Phase I clinical trial devoid of FFA rebound. 

Suggested Best Practices for Chemists 1. Claims in a patent application tend to begin broadly and then narrow down to important individual compounds. Scrutinize application claims to make sure the most important compounds (e.g., clinical candidates and backups) are individually claimed. One important compound = one claim. 

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