Ian B. Campbell

Factors Determining the Selection of Organic Reactions by Medicinal Chemists and the Use of These Reactions in Arrays (Small Focused Libraries)

Synthetic organic reactions are a fundamental enabler of small-molecule drug discovery, and the vast majority of medicinal chemists are initially trained--either at universities or within industry--as synthetic organic chemists. The sheer breadth of synthetic methodology available to the medicinal chemist represents an almost endless source of innovation. But what reactions do medicinal chemists use in drug discovery? And what criteria do they use in selecting synthetic methodology? Why are arrays (small focused libraries) so powerful in the lead-optimization process? In this Minireview, we suggest some answers to these questions and also describe how we have tried to expand the number of robust reactions available to the medicinal chemist.

Rhodium carbene routes to oxazoles and thiazoles. Catalyst effects in the synthesis of oxazole and thiazole carboxylates, phosphonates, and sulfones.

Dirhodium tetraacetate catalyzed reaction of alpha-diazo-beta-keto-carboxylates and -phosphonates with arenecarboxamides gives 2-aryloxazole-4-carboxylates and 4-phosphonates by carbene N-H insertion and cyclodehydration. In stark contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates. Alpha-diazo-beta-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides. The analogous reactions of thiocarboxamides give the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones.

A concise route to pyridines from hydrazides by metal carbene N-H insertion, 1,2,4-triazine formation, and Diels-Alder reaction.

A simple, new three-step sequence for the conversion of hydrazides into pyridines is reported in which the key steps are N-H insertion by a copper carbene intermediate derived from alpha-diazo-beta-ketoesters into the hydrazide, reaction with ammonium acetate to give 1,2,4-triazines, followed by Diels-Alder reaction with norbornadiene.

A simple and effective synthetic approach to chiral 4-pyridinyl proline derivatives

A rapid approach has been developed to provide a novel series of 4-pyridinyl proline derivatives as potential stereoselective catalysts. Nucleophilic displacement at the 4-pyridinyl position proved straightforward using proline but required microwave heating to proceed when using the more bulky α-methyl proline. Total control of enantioselectivity was obtained for the synthesis of proline derivatives.

A simple solid phase diversity linker strategy using enol phosphonates.

Polymer bound lactam enol phosphonates can be easily generated using simple phenol on polystyrene resin. These stable, storable compounds can be released in a diversity cleavage strategy, using Suzuki cross coupling conditions, to provide 2-arylenamides in moderate to good overall yields.

Identification and optimisation of a novel series of pyrimidine based cyclooxygenase-2 (COX-2) inhibitors. Utilisation of a biotransformation approach

Many years of work have been invested in the identification of potent and selective COX-2 inhibitors for the treatment of chronic inflammatory pain. One issue faced by workers is the balance between the lipophilicity required for potent enzyme inhibition and the physical properties necessary for drug absorption and distribution in vivo. Frequently approaches to reduce lipophilicity through introduction of polar functionality is hampered by highly challenging chemistry to prepare key molecules. We have complemented traditional synthetic chemistry with a biotransformations approach which efficiently provided access to an array of key target molecules.

A practical drug discovery project at the undergraduate level.

In this article, we describe a practical drug discovery project for third-year undergraduates. No previous knowledge of medicinal chemistry is assumed. Initial lecture workshops cover the basic principles; then students, in teams, seek to improve the profile of a weakly potent, insoluble phosphatidylinositide 3-kinase delta (PI3Kδ) inhibitor (1) through compound array design, molecular modelling, screening data analysis and the synthesis of target compounds in the laboratory. The project benefits from significant industrial support, including lectures, student mentoring and consumables. The aim is to make the learning experience as close as possible to real-life industrial situations. In total, 48 target compounds were prepared, the best of which (5b, 5j, 6b and 6ap) improved the potency and aqueous solubility of the lead compound (1) by 100-1000 fold and ≥tenfold, respectively.

Medicinal chemistry in drug discovery in big pharma: past, present and future

The changes in synthetic and medicinal chemistry and related drug discovery science as practiced in big pharma over the past few decades are described. These have been predominantly driven by wider changes in society namely the computer, internet and globalisation. Thoughts about the future of medicinal chemistry are also discussed including sharing the risks and costs of drug discovery and the future of outsourcing. The continuing impact of access to substantial computing power and big data, the use of algorithms in data analysis and drug design are also presented. The next generation of medicinal chemists will communicate in ways that reflect social media and the results of constantly being connected to each other and data.

Simultaneous high throughput assessment of thermodynamic and kinetic behaviour of chemical reactions: theory and experiment

There is an increasing requirement in the pharmaceutical industry to rapidly monitor reactions. High throughput screening (HTS) is typically achieved by performing experiments simultaneously in array format in microtitre plates. One method of monitoring reactions that has received particular attention recently is the use of thermal measurements. The change in temperature with time resulting from a reaction depends on both thermodynamics and kinetics. Temperature can be monitored in a number of ways, one of which suitable for HTS is thermographic imaging. Relating such thermal information to reaction parameters such as enthalpy and rate is complicated by issues such as heat loss to the surroundings and heat transfer to different parts of the apparatus. A method is presented whereby information obtained from thermal imaging of microtitre plates can be used, along with experimental data for heat transfer to the surroundings and the microtitre plate, to rank reaction enthalpy and time to completion of a set of reactions. Finally a comparison to enthalpies obtained by microcalorimetry is made.

Base-Controlled Diastereoselective Synthesis of Either anti- or syn-β-Aminonitriles

Deprotonation of secondary alkane nitriles with nBuLi and addition to aryl imines gives kinetic anti-β-aminonitriles. Use of LHMDS allows reversible protonation of the reaction intermediate to give syn-β-aminonitriles. The pure diastereosiomers can be isolated in good yields, and the mechanism was elucidated.