Pyrrolo[2,1-f][1,2,4]triazines: From C-nucleosides to kinases and back again, the remarkable journey of a versatile nitrogen heterocycle.

Pyrrolo[2,1-f][1,2,4]triazine, a unique NN bond-containing heterocycle with a bridgehead nitrogen, was first synthesized in the late 1970s but did not find utility until more than a decade later in the early 1990s when it was incorporated into C-nucleosides as a novel purine-like mimetic. This heterocycle remained at the fringes of medicinal chemistry until a confluence of events spurred by the explosion of the kinase inhibitor field in the early 2000s and the pressing need for novel, druggable scaffolds to occupy that exciting space led to numerous applications against diverse therapeutic targets. This digest will explore the history of this scaffold and the importance of chemistry in propelling drug discovery. The varied uses of this scaffold will be detailed as it progressed from C-nucleosides, to kinase inhibitors, to recognition as a "privileged" template, and finally reemergence in the C-nucleoside field.

Chemically Diverse Group I p21-Activated Kinase (PAK) Inhibitors Impart Acute Cardiovascular Toxicity with a Narrow Therapeutic Window.

p21-activated kinase 1 (PAK1) has an important role in transducing signals in several oncogenic pathways. The concept of inhibiting this kinase has garnered significant interest over the past decade, particularly for targeting cancers associated with PAK1 amplification. Animal studies with the selective group I PAK (pan-PAK1, 2, 3) inhibitor G-5555 from the pyrido[2,3-d]pyrimidin-7-one class uncovered acute toxicity with a narrow therapeutic window. To attempt mitigating the toxicity, we introduced significant structural changes, culminating in the discovery of the potent pyridone side chain analogue G-9791. Mouse tolerability studies with this compound, other members of this series, and compounds from two structurally distinct classes revealed persistent toxicity and a correlation of minimum toxic concentrations and PAK1/2 mediated cellular potencies. Broad screening of selected PAK inhibitors revealed PAK1, 2, and 3 as the only overlapping targets. Our data suggest acute cardiovascular toxicity resulting from the inhibition of PAK2, which may be enhanced by PAK1 inhibition, and cautions against continued pursuit of pan-group I PAK inhibitors in drug discovery.

Serendipity in drug-discovery: a new series of 2-(benzyloxy)benzamides as TRPM8 antagonists.

A new series of 2-(benzyloxy)benzamides are presented that are potent functional antagonists of TRPM8 and possess improved LipE and LE compared to the original lead. They were discovered through a series of compound libraries and we present a powerful visualization method for the chemical space explored with each library. Remarkably this new series originated from the highest risk design strategy where compounds were synthesised with the least degree of similarity to the lead structure.

Sulfonamides as selective oestrogen receptor ß agonists.

A series of p-hydroxybenzenesulphonamides ERß receptor agonists were discovered and several compounds identified had excellent selectivity over the related ERα receptor. One of these, compound 11, had an interesting binding conformation determined by X-ray and represents an excellent starting point in the quest for further selective ERß agonists.

Discovery of PF-00217830: aryl piperazine napthyridinones as D2 partial agonists for schizophrenia and bipolar disorder.

The synthesis and structure-activity relationship (SAR) of a novel series of aryl piperazine napthyridinone D(2) partial agonists is described. Our goal was to optimize the affinities for the D(2), 5-HT(2A) and 5-HT(1A) receptors, such that the D(2)/5-HT(2A) ratio was greater than 5 to ensure maximal occupancy of these receptors when the D(2) occupancy reached efficacious levels. This strategy led to identification of PF-00217830 (2) with robust inhibition of sLMA (MED=0.3mg/kg) and DOI-induced head twitches in rats (31% and 78% at 0.3 and 1mg/kg) with no catalepsy observed at the highest dose tested (10 mg/kg).

6-Alkoxyisoindolin-1-one based dopamine D2 partial agonists as potential antipsychotics.

A series of 6-alkoxyisoindolin-1-ones with a magic shotgun pharmacological profile are presented as potential antipsychotics. The in vitro pharmacological profile includes D(2) partial agonism (30-55%), 5-HT(1A) partial agonism (60-90%), and 5-HT(2A) antagonism. Selected compounds in this series displayed good in vivo activity and potency.

Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis.

The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.

Azide and Cyanide Displacements via Hypervalent Silicate Intermediates.

Hypervalent azido- and cyanosilicate derivatives, prepared in situ by the reaction of trimethylsilyl azide or trimethylsilyl cyanide, respectively, with tetrabutylammonium fluoride, are effective sources of nucleophilic azide or cyanide. Primary and secondary alkyl halides and sulfonates undergo rapid and efficient azide or cyanide displacement in the absence of phase transfer catalysts with the silicate derivatives. Application of these reagents to the stereoselective synthesis of glycosyl azide derivatives is reported.