Structural studies on bioactive compounds. 34. Design, synthesis, and biological evaluation of triazenyl-substituted pyrimethamine inhibitors of Pneumocystis carinii dihydrofolate reductase

Approaches to the Structure-Based Design of Antivirulence Drugs: Therapeutics for the Post-Antibiotic Era

The alarming rise of multidrug-resistant bacterial strains, coupled with decades of stagnation in the field of antibiotic development, necessitates exploration of new therapeutic approaches to treat bacterial infections. Targeting bacterial virulence is an attractive alternative to traditional antibiotics in that this approach disarms pathogens that cause human diseases, without placing immediate selective pressure on the target bacterium or harming commensal species. The growing number of validated virulence protein targets for which structural information has been obtained, along with advances in computational power and screening algorithms, make the rational design of antivirulence drugs a promising avenue to explore. Here, we review the principles of structure-based drug design and the exciting opportunities this technique presents for antivirulence drug discovery.

Dihydrofolate reductase inhibitors: developments in antiparasitic chemotherapy

BACKGROUND

Infections caused by parasitic protozoa present a growing health concern, particularly in developing parts of the world. Although malaria is clearly the most well-known and deadly of these diseases, infections caused by other parasites, such as Toxoplasma, Cryptosporidia and Trypanosoma are emerging infectious threats. The success of inhibitors of the enzyme dihydrofolate reductase (DHFR) against malaria has encouraged further exploration of this strategy against other parasites.

OBJECTIVE

This review presents antifolate inhibitors that have appeared in the patent literature and elaborates on their potency and selectivity against the DHFR enzyme from parasitic protozoa.

METHODS

The patent literature since 1994 was surveyed for antiparasitic DHFR inhibitors.

RESULTS/CONCLUSIONS

Over the past several years, there have been a variety of novel, potent and selective inhibitors disclosed in patents, primarily from academic researchers. This review summarizes the recent development of antifolates as specific agents against parasitic protozoa.

Dihydrofolate reductase as a therapeutic target for infectious diseases: opportunities and challenges

Infectious diseases caused by parasites continue to take a massive toll on human health in the poor regions of the world. Filling the anti-infective drug-discovery pipeline has never been as challenging as it is now. The organisms responsible for these diseases have interesting biology with many potential biochemical targets. Inhibition of metabolic enzymes has been established as an attractive strategy for anti-infectious drug development. In this field, dihydrofolate reductase (DHFR) is an important enzyme in nucleic and amino acid synthesis and an extensively studied drug target over the past 50 years. The challenges for novel DHFR inhibition-based chemotherapeutics for the treatment of infectious diseases are now focused on overcoming the resistance problem as well as cost–effectiveness. Each year, the large number of literature citations attest the continued popularity of DHFR. It becomes truly the ‘enzyme of choice for all seasons and almost all reasons’. Herein, we summarize the opportunities and challenges in developing novel lead based on this target.

Structure-based discovery of antibacterial drugs

The modern era of antibacterial chemotherapy began in the 1930s, and the next four decades saw the discovery of almost all the major classes of antibacterial agents that are currently in use. However, bacterial resistance to many of these drugs is becoming an increasing problem. As such, the discovery of drugs with novel modes of action will be vital to meet the threats created by the emergence of resistance. Success in discovering inhibitors using high-throughput screening of chemical libraries is rare. In this Review we explore the exciting opportunities for antibacterial-drug discovery arising from structure-based drug design.

Dihydrofolate reductase inhibitors as antibacterial agents

Although only a few DHFR inhibitors have progressed as antibiotics to the market there is much renewed interest in the discovery and development of new generation DHFR inhibitors as antibacterial agents. This article describes the success in exploiting DHFR as a drugable target as exemplified by trimethoprim (TMP) and the development of several new diaminopyrimidines. Iclaprim, a recent example of a novel diaminopyrimidine currently in Phase III clinical trials, is also described together with several examples of anti-DHFR antibacterial compounds in pre-clinical development.

The process of structure-based drug design

The field of structure-based drug design is a rapidly growing area in which many successes have occurred in recent years. The explosion of genomic, proteomic, and structural information has provided hundreds of new targets and opportunities for future drug lead discovery. This review summarizes the process of structure-based drug design and includes, primarily, the choice of a target, the evaluation of a structure of that target, the pivotal questions to consider in choosing a method for drug lead discovery, and evaluation of the drug leads. Key principles in the field of structure-based drug design will be illustrated through a case study that explores drug design for AmpC beta-lactamase.

Iclaprim, a novel diaminopyrimidine with potent activity on trimethoprim sensitive and resistant bacteria

Iclaprim, a new selective dihydrofolate inhibitor was synthesized based on rational drug design. Iclaprim's interaction with a resistant Staphylococcus aureus dihydrofolate reductase (DHFR) is outlined in comparison to trimethoprim (TMP). This compound is active against methicillin, TMP and vancomycin resistant strains. Arpida Ltd. is developing Iclaprim for serious hospital infections from Gram-positive pathogens and respiratory tract infections.

Strategies for the determination of bioactive phenols in plants, fruit and vegetables

Analytical strategies dealing with bioactive phenols in plants and foods are reviewed. These depend on the purpose of the analysis which may be classified as studies where the principal purpose is biological screening, phytochemical and/or chemical screening. Nevertheless, extraction of the phenol from the sample matrix is common and methods of achieving a suitable extract are assessed. Advances in the separation sciences and spectrometry are exploited for identification and quantification of isolated phenols. The various procedures are summarized and some typical "case studies" are presented. Two important areas are introduced briefly. Thus, plant phenols are reactive species and their ultimate fate has been relatively neglected. Studies of bioactive compounds generate a considerable volume of data making data handling and informatics important topics that warrant a separate review.

Structural studies on bioactive compounds. Part 36: design, synthesis and biological evaluation of pyrimethamine-based antifolates against Pneumocystis carinii

As part of a research effort to improve the quality of current chemotherapy of Pneumocystis carinii pneumonia, we report a structure-based design project to optimise activity, species selectivity and pharmaceutical properties of the triazenyl-pyrimethamine TAB (4) (IC(50)=0.17 microM; rat liver DHFR IC(50)/P. carinii DHFR IC(50)=114). This has led us to design, synthesise and evaluate four new series of pyrimethamine derivatives bearing triazole, triazolium, triazinium and amino moieties at the 3'-position of the p-chlorophenyl ring. Such stabilised 'triazene' derivatives address the potentially compromised pharmaceutical profile of TAB and the 3'-amine substituted agents afford conformationally flexible substitutes. The benzylamino-pyrimethamine derivative (24a) (IC(50)=0.12 microM, rat liver DHFR IC(50)/P. carinii DHFR IC(50): 5.26) was the most potent and the only P. carinii-selective antifolate of the new series.