Total Synthesis of (-)-Luminacin D.

A second-generation synthesis of (-)-luminacin D based on an early stage introduction of the trisubstituted epoxide group is reported, allowing access to the natural product in an improved yield and a reduced number of steps (5.4%, 17 steps vs 2.6%, 19 steps). A full account of the optimization work is provided, with the reversal of stereoselection in the formation of the C4 alcohol in equally excellent diastereoselectivity as the key improvement.

Molecular hybridization yields triazole bronchodilators for the treatment of COPD.

A 1,2,4-triazole motif was employed as a bioisostere for the ester commonly used in muscarinic antagonists, and subsequent integrative conjugation to a ß2 agonist quinolinone furnished a new class of bifunctional MABAs for the treatment of COPD. Medicinal chemistry optimization using the principles of 'inhalation by design' furnished a clinical candidate with desirable pharmacological, pharmacokinetic and biopharmaceutical properties.

Stereocontrol by quaternary centres: a stereoselective synthesis of (-)-luminacin D.

Very high diastereoselectivity can be achieved by 1,3-chelation-controlled allylation of aldehydes that possess a non-chelating α-ether substituent, even if the α-position is a quaternary centre and/or a spiro-epoxide. This reaction was used as a key step in an enantioselective synthesis of the angiogenesis inhibitor luminacin D.

Synthesis of novel histamine H4 receptor antagonists.

This letter describes the discovery and synthesis of a series of octahydropyrrolo[3,4-c]pyrrole based selective histamine hH4 receptor antagonists. The amidine compound 20 was found to be a potent and selective histamine H4 receptor antagonist with moderate clearance and a high volume of distribution.

Click-enabled heterotrifunctional template for sequential bioconjugations.

A heterotrifunctional template was developed that utilizes thiol-maleimide and click chemistries (both copper-free and copper-mediated) to effect sequential biomolecule conjugations in a one-pot process. The breadth of compatible substrates was illustrated through highly efficient conjugations of protein, peptide, sugar, lipid, fluoroalkane, biotin and fluorophore molecules. This template should be useful for the creation of chemically-enhanced/enabled biotherapeutics, especially through the expression of discontinuous (and heterogeneous) epitopes.

Discovery of a series of potent and selective human H4 antagonists using ligand efficiency and libraries to explore structure-activity relationship (SAR).

We describe the identification of a potent, selective lead series that shows antagonism against the human histamine H4 receptor from thirteen actives identified in an HTS as part of a hit to lead program. By focusing on ligand efficiency and concurrently using a diversity based approach, compounds based around 2,4-diaminopyrimidine were identified with compound 25 being quickly shown to be a good lead. It also had the highest ligand efficiency in the series.

Design and synthesis of long acting inhaled corticosteroids for the treatment of asthma.

In this Letter we present data for a novel series of ICS for the treatment of asthma. 'Inhalation by design' principles have been applied to a series of highly potent steroidal GR agonists, with a focus on optimising the potential therapeutic index in human. Pharmacokinetic properties were tuned with high intrinsic clearance and low oral bioavailability in mind, to minimise systemic exposure and reduce systemically driven adverse events. High CYP mediated clearance as well as glucuronidation were targeted to achieve high intrinsic clearance coupled with multiple routes of clearance to minimise drug-drug interactions. Furthermore, pharmaceutical properties such as stability, crystallinity and solubility were considered to ensure compatibility with a dry powder inhaler. This work culminated in the identification of the clinical candidate 15, which demonstrates preclinically the desired efficacy and safety profiles confirming its potential as an inhaled agent for the treatment of asthma.

Inhalation by design: dual pharmacology ß-2 agonists/M3 antagonists for the treatment of COPD.

This paper describes the successful design and development of dual pharmacology ß-2 agonists-M3 antagonists, for the treatment of chronic obstructive pulmonary disorder using the principles of 'inhalation by design'. A key feature of this work is the combination of balanced potency and pharmacodynamic duration with desirable pharmacokinetic and material properties, whilst keeping synthetic complexity to a minimum.

The Chemical Synthesis of Knob Domain Antibody Fragments.

Cysteine-rich knob domains found in the ultralong complementarity determining regions of a subset of bovine antibodies are capable of functioning autonomously as 3-6 kDa peptides. While they can be expressed recombinantly in cellular systems, in this paper we show that knob domains are also readily amenable to a chemical synthesis, with a co-crystal structure of a chemically synthesized knob domain in complex with an antigen showing structural equivalence to the biological product. For drug discovery, following the immunization of cattle, knob domain peptides can be synthesized directly from antibody sequence data, combining the power and diversity of the bovine immune repertoire with the ability to rapidly incorporate nonbiological modifications. We demonstrate that, through rational design with non-natural amino acids, a paratope diversity can be massively expanded, in this case improving the efficacy of an allosteric peptide. As a potential route to further improve stability, we also performed head-to-tail cyclizations, exploiting the proximity of the N and C termini to synthesize functional, fully cyclic antibody fragments. Lastly, we highlight the stability of knob domains in plasma and, through pharmacokinetic studies, use palmitoylation as a route to extend the plasma half-life of knob domains in vivo. This study presents an antibody-derived medicinal chemistry platform, with protocols for solid-phase synthesis of knob domains, together with the characterization of their molecular structures, in vitro pharmacology, and pharmacokinetics.

Pyrazole NNRTIs 4: selection of UK-453,061 (lersivirine) as a development candidate.

We prepared three discreet cohorts of potent non-nucleoside HIV reverse transcriptase inhibitors (NNRTIs) based on the recently reported 3-cyanophenoxypyrazole lead 3. Several of these compounds displayed very promising anti-HIV activity in vitro, safety, pharmacokinetic and pharmaceutical profiles. We describe our analysis and conclusions leading to the selection of alcohol 5 (UK-453,061, lersivirine) for clinical development.

Pyrazole NNRTIs 3: optimisation of physicochemical properties.

Our efforts to reduce overall lipophilicity and increase ligand-lipophilicity efficiency (LLE) by modification of the 3- and 5-substituents of pyrazole 1, a novel non-nucleoside HIV reverse transcriptase inhibitor (NNRTI) prototype were unsuccessful. In contrast replacement of the substituted benzyl group with corresponding phenylthio or phenoxy groups resulted in marked improvements in potency, ligand efficiency (LE) and LLE.

SAR of a series of inhaled A(2A) agonists and comparison of inhaled pharmacokinetics in a preclinical model with clinical pharmacokinetic data.

COPD is a major cause of mortality in the western world. A(2A) agonists are postulated to reduce the lung inflammation that causes COPD. The cardiovascular effects of A(2A) agonists dictate that a compound needs to be delivered by inhalation to be therapeutically useful. The pharmacological and pharmacokinetic SAR of a series of inhaled A(2A) agonists is described leading through to human pharmacokinetic data for a clinical candidate.

Inhaled adenosine A(2A) receptor agonists for the treatment of chronic obstructive pulmonary disease.

COPD is a major cause of mortality in the western world. A(2A) agonists are postulated to reduce the lung inflammation that causes COPD. The cardiovascular effects of A(2A) agonists dictate that a compound needs to be delivered by inhalation to be therapeutically useful. A strategy of minimizing side-effect liability by maximizing systemic clearance was followed and pharmacological and pharmacokinetic SAR of a series of inhaled A(2A) agonists described. A sevenfold improvement in potency and 150-fold reduction in side-effect liability over the lead compound CGS-21680, were obtained.

Selection of a novel anti-nicotine vaccine: influence of antigen design on antibody function in mice.

Anti-nicotine vaccines may aid smoking cessation via the induction of anti-nicotine antibodies (Ab) which reduce nicotine entering the brain, and hence the associated reward. Ab function depends on both the quantity (titer) and the quality (affinity) of the Ab. Anti-nicotine vaccines tested previously in clinical studies had poor efficacy despite high Ab titer, and this may be due to inadequate function if Ab of low affinity were induced. In this study, we designed and synthesized a series of novel nicotine-like haptens which were all linked to diphtheria toxoid (DT) as carrier, but which differed in the site of attachment of linker to nicotine, the nature of linker used, and the handle used to attach the hapten to DT. The resulting hapten conjugates were evaluated in a mouse model, using CpG (a TLR9 agonist) and aluminum hydroxide (Al(OH)3) as adjuvants, whereby Ab titers, affinity and function were evaluated using a radiolabeled nicotine challenge model. A series of additional linkers varying in length, rigidity and polarity were used with a single hapten to generate additional DT-conjugates, which were also tested in mice. Conjugates made with different haptens resulted in various titers of anti-nicotine Ab. Several haptens gave similarly high Ab titers, but among these, Ab affinity and hence function varied considerably. Linker also influenced Ab titer, affinity and function. These results demonstrate that immune responses induced in mice by nicotine-conjugate antigens are greatly influenced by hapten design including site of attachment of linker to nicotine, the nature of linker used, and the handle used to attach the hapten to DT. While both Ab titer and affinity contributed to function, affinity was more sensitive to antigen differences.

A perspective on synthetic and solid-form enablement of inhalation candidates.

The administration of compounds by a dry-powder inhaler presents significant challenges to the development and discovery chemist, owing to the stringent requirements placed upon the physical characteristics of the active pharmaceutical ingredient and the high complexity of the molecules concerned. The current state of synthetic chemistry technology is such that commercial syntheses of these compounds are demanding but achievable. While synthetic chemistry will remain a major component of the development of inhaled therapies, the main challenge facing practitioners in this area is the early identification of a suitable solid form. Further advances in the prediction of solid-form properties would significantly enable this field and may allow triage of molecules to be carried out at the design stage of projects.

In-cell click labelling of small molecules to determine subcellular localisation.

UNLABELLED: Small molecule fluorometric boron dipyrromethene probes were developed to bind hepatitis C virus-encoded NS5A protein and aid subcellular distribution studies. These molecules did not co-locate with NS5A, therefore alternative 'silent' azide reporters were used to obtain a more relevant picture of their distribution. Following pre-incubation with replicon cells, click chemistry was used to append a fluorophore to the azide that confirmed the co-localisation of the small molecule with the NS5A protein, thus providing greater insight into the antiviral mode of action of this chemotype. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12154-010-0047-1) contains supplementary material, which is available to authorized users.

Enantioselective total syntheses of omuralide, 7-epi-omuralide, and (+)-lactacystin.

An alkylidene carbene 1,5-CH insertion has been used as a key step in an enantioselective total syntheses of omuralide, its C7-epimer, and (+)-lactacystin. An additional noteworthy feature of the synthesis is the use of a novel oxidative deprotection procedure, utilizing DMDO, for the conversion of a late-stage benzylidene acetal into a primary alcohol and a secondary benzoate ester.

Synthetic chemistry-led creation of a difluorinated biaryl ether non-nucleoside reverse transcriptase inhibitor.

In the process of developing a series of novel, fluorinated biaryl ether NNRTIs, we fortuitously discovered derivative 20, which possesses excellent potency against both wild-type and clinically relevant mutations of the reverse transcriptase enzyme.

Enantioselective total syntheses of (-)-clasto-lactacystin beta-lactone and 7-epi-(-)-clasto-lactacystin beta-lactone.

An alkylidene carbene 1,5-CH insertion has been used as a key step in an efficient enantioselective total synthesis of (-)-clasto-lactacystin beta-lactone, and its C7-epimer. An additional noteworthy feature of the synthesis is the use of a novel oxidative deprotection procedure, utilizing DMDO, for the conversion of a late-stage benzylidene acetal into a primary alcohol and a secondary benzoate ester.