Novel azepane derivatives were prepared and evaluated for protein kinase B (PKB-alpha) and protein kinase A (PKA) inhibition. The original (-)-balanol-derived lead structure (4R)-4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzoic acid (3R)-3-[(pyridine-4-carbonyl)amino]-azepan-4-yl ester (1) (IC(50) (PKB-alpha) = 5 nM) which contains an ester moiety was found to be plasma unstable and therefore unsuitable as a drug. Based upon molecular modeling studies using the crystal structure of the complex between PKA and 1, the five compounds N-[(3R,4R)-4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzoylamino]-azepan-3-yl]-isonicotinamide (4), (3R,4R)-N-[4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzyloxy]-azepan-3-yl]-isonicotinamide (5), N-[(3R,4S)-4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-phenylamino]-methyl]-azepan-3-yl)-isonicotinamide (6), N-[(3R,4R)-4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzylamino]-azepan-3-yl]-isonicotinamide (7), and N-[(3R,4S)-4-(4-[trans-2-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-phenyl]-vinyl]-azepan-3-yl)-isonicotinamide (8) with linkers isosteric to the ester were designed, synthesized, and tested for in vitro inhibitory activity against PKA and PKB-alpha and for plasma stability in mouse plasma.(1) Compound 4 was found to be plasma stable and highly active (IC(50) (PKB-alpha) = 4 nM). Cocrystals with PKA were obtained for 4, 5, and 8 and analyzed for binding interactions and conformational changes in the ligands and protein in order to rationalize the different activities of the molecules.

Although many drugs are based on single-substrate analogues, it is well appreciated that enzymes often require, in addition to a substrate, a cofactor for function. The rational design of inhibitors, where a substrate analogue and a cofactor analogue are covalently linked to form a bisubstrate inhibitor, may provide innovative new lead structures in medicinal chemistry that feature both enhanced binding affinity and binding-site selectivity. Some attempts have been made to construct bisubstrate inhibitors for kinases which target both the ATP and the substrate binding sites. [1,2] Other important targets are methyltransferases that depend on S-adenosylmethionine (SAM). The enzyme catechol-O-methyltransferase (COMT) catalyzes the methylation of biologically active catechols, such as l-dopa and dopamine, in the presence of SAM and Mg 2 ions. The addition of COMT inhibitors to levodopa reduces the extracerebral catabolism of levodopa and increases its elimination half-life, thus ensuring that a higher quantity of orally administered l-dopa reaches its target in the brain. [3] This situation produces a stronger and longer lasting therapeutic effect in patients with Parkinsons disease. Nitro-substituted catechols were found to be potent COMT inhibitors, and two derivatives (tolcapone (Tasmar) and entecapone (Comptan)) have been introduced into the marketplace. [3] Recently, we described the first effective bisubstrate inhibitor 1 for COMT (IC 50 2 mm; IC 50 concentration of inhibitor at which 50 % inhibition of the enzyme is observed) which was developed by rational design using the crystal structure of the quaternary complex between the enzyme, SAM, 3,5-dinitrocatechol, and a Mg 2 ion. [4±6]

Protein kinase B (PKB)-selective inhibitors were designed, synthesized, and cocrystallized using the AGC kinase family protein kinase A (PKA, often called cAMP-dependent protein kinase); PKA has been used as a surrogate for other members of this family and indeed for protein kinases in general. The high homology between PKA and PKB includes very similar ATP binding sites and hence similar binding pockets for inhibitors, with only few amino acids that differ between the two kinases. A series of these sites were mutated in PKA in order to improve the surrogate model for a design of PKB-selective inhibitors. Namely, the PKA to PKB exchanges F187L and Q84E enable the design of the selective inhibitors described herein which mimic ATP but extend further into a site not occupied by ATP. In this pocket, selectivity over PKA can be achieved by the introduction of bulkier substituents. Analysis of the cocrystal structures and binding studies were performed to rationalize the selectivity and improve the design.

Inhibition of the enzyme catechol-O-methyltransferase (COMT) is an important approach in the treatment of Parkinson's disease. A series of new potent bisubstrate inhibitors for COMT, resulting from X-ray structure-based design and featuring adenosine and catechol moieties have been synthesised. Biological results show a large dependence of binding affinity on inhibitor preorganisation and the length of the linker between nucleoside and catechol moieties. The most potent bisubstrate inhibitor for COMT has an IC50 value of 9 nM. It exhibits competitive kinetics for the SAM and mixed inhibition kinetics for the catechol binding site. Its bisubstrate binding mode was confirmed by X-ray structure analysis of the ternary complex formed by the inhibitor, COMT and a Mg2+ ion.

The enzyme catechol O-methyltransferase (COMT) catalyzes the Me group transfer from the cofactor S-adenosylmethionine (SAM) to the hydroxy group of catechol substrates. Potential bisubstrate inhibitors of COMT were developed by structure-based design and synthesized. The compounds were tested for in vitro inhibitory activity against COMT obtained from rat liver, and the inhibition kinetics were examined with regard to the binding sites of cofactor and substrate. One of the designed molecules was found to be a bisubstrate inhibitor of COMT with an IC50 = 2 microM. It exhibits competitive kinetics for the SAM and noncompetitive kinetics for the catechol binding site. Useful structure-activity relationships were established which provide important guidelines for the design of future generations of bisubstrate inhibitors of COMT.

The reactivity of a range of pyridone and pyrazinone derivatives towards alkynes in the presence of cyclopentadienylcobaltbis(ethene) has been investigated. Depending on the nature of the substrates, [2+2+2]- or [2+2] cycloaddition, C-H, or N-H activation may occur. In the case of pyridones, the first three predominated with N-protected derivatives, whereas substrates containing N-H bonds followed an N-H activation pathway. The [2+2+2] cycloaddition of an N-butynylisoquinolone was applied successfully to the total synthesis of anhydrolycorinone. Pyrazinone substrates showed similar patterns of reactivity.

With an IC50 value of 9 nM, 1 is the most potent known disubstrate inhibitor for catechol‐O‐methyltransferase (COMT). Inhibition of COMT is of significant interest in the therapy of Parkinsonapos;s disease since it ensures that a larger percentage of orally administered L‐dopa reaches—in the form of dopamine—its target in the brain. The X‐ray crystal structure of a complex formed by COMT and 1 has been solved at 2.6‐Å resolution.

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