From pyrroles to 1-oxo-2,3,4,9-tetrahydro-1H-β-carbolines: A new class of orally bioavailable mGluR1 antagonists

β-Carboline as a Privileged Scaffold for Multitarget Strategies in Alzheimer's Disease Therapy

The natural β-carboline alkaloids display similarities with neurotransmitters that can be favorably exploited to design bioactive and bioavailable drugs for Alzheimer's disease (AD) therapy. Several AD targets are currently and intensively being investigated, divided in different hypotheses: mainly the cholinergic, the amyloid β (Aβ), and the Tau hypotheses. To date, only symptomatic treatments are available involving acetylcholinesterase and NMDA inhibitors. On the basis of plethoric single-target structure-activity relationship studies, the β-carboline scaffold was identified as a powerful tool for fostering activity and molecular interactions with a wide range of AD-related targets. This knowledge can undoubtedly be used to design multitarget-directed ligands, a highly relevant strategy preferred in the context of multifactorial pathology with intricate etiology such as AD. In this review, we first individually discuss the AD targets of the β-carbolines, and then we focus on the multitarget strategies dedicated to the deliberate design of new efficient scaffolds.

General and efficient synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones via a formal [3 + 2] cycloaddition initiated by C–H activation

A [Cp*RhCl₂]₂-catalyzed formal [3 + 2] cycloaddition involving a sequential coupling reaction initiated by C–H activation and aza-Michael addition has been developed for the general and efficient synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones.

Fragment-Based Approaches for Allosteric Metabotropic Glutamate Receptor (mGluR) Modulators

Metabotropic glutamate receptors (mGluR) are members of the class C G-Protein Coupled Receptors (GPCR-s) and have eight subtypes. These receptors are responsible for a variety of functions in the central and peripheral nervous systems and their modulation has therapeutic utility in neurological and psychiatric disorders. It was previously established that selective orthosteric modulation of these receptors is challenging, and this stimulated the search for allosteric modulators. Fragment-Based Drug Discovery (FBDD) is a viable approach to find ligands binding at allosteric sites owing to their limited size and interactions. However, it was also observed that the structure-activity relationship of allosteric modulators is often sharp and inconsistent. This can be attributed to the characteristics of the allosteric binding site of mGluRs that is a water channel where ligand binding is accompanied with induced fit and interference with the water network, both playing a role in receptor activation. In this review, we summarize fragment-based drug discovery programs on mGluR allosteric modulators and their contribution identifying of new mGluR ligands with better activity and selectivity.

Iron(III)-Catalyzed (4 + 2)-Cycloannulation of 2-Hydroxy Ketoxime Ethers with Indol-2-ylamides: Synthesis of Indole-Fused 2-Piperidinones

A highly regio- and diastereoselective (4 + 2)-cycloannulation process of indanone-derived 2-hydroxy ketoxime ethers with 1,4-bisnucleophilic indol-2-ylamides has been developed. In the presence of 5 mol % FeCl₃, densely functionalized 2-piperidinones containing two new σ-bonds and two vicinal quaternary stereogenic centers were formed under mild reaction conditions in a one-pot operation. Moreover, most of the products directly precipitated out of the solution and were isolated by simple filtration without purification by column chromatography.

Crystal structure of methyl 1-methyl-2-oxo-spiro-[indoline-3,2'-oxirane]-3'-carboxyl-ate

In the title compound, C12H11NO4, the dihedral angle between the indole ring system (r.m.s. deviation = 0.019 Å) and the oxirane ring is 88.8 (2)°. The oxirane O atom and the bridging ester O atom are in an approximate syn conformation [O-C-C-O = -25.4 (3)°] In the crystal, inversion dimers linked by pair of C-H⋯O hydrogen bonds generate R 2 (2)(8) loops, where the C-H donor group forms part of the oxirane ring. A second C-H⋯O inter-action arising from one of the C-H groups of the benzene ring links the dimers into [001] double chains.

Photochemistry of benzotriazoles: generation of 1,3-diradicals and intermolecular cycloaddition as a new route toward indoles and dihydropyrrolo[3,4-b]indoles

Irradiation of benzotriazoles 1a–e at λ = 254 nm in acetonitrile solution generated the corresponding 1,3-diradicals which underwent intermolecular cycloaddition with maleimides to afford the corresponding dihydropyrrolo[3,4-b]indoles and with acetylene derivatives to afford indoles as the major products. This offers an interesting and simple access to such ring systems of potential synthetic and biological interest. The structures of the photoproducts were established spectroscopically and by single crystal X-ray crystallography.

Design, Synthesis, and Biological Evaluation of PKD Inhibitors

Protein kinase D (PKD) belongs to a family of serine/threonine kinases that play an important role in basic cellular processes and are implicated in the pathogenesis of several diseases. Progress in our understanding of the biological functions of PKD has been limited due to the lack of a PKD-specific inhibitor. The benzoxoloazepinolone CID755673 was recently reported as the first potent and kinase-selective inhibitor for this enzyme. For structure-activity analysis purposes, a series of analogs was prepared and their in vitro inhibitory potency evaluated.

3,4-Dibromo-2,5-bis[(diethoxyphosphoryl)methyl]-1-phenylsulfonyl-1H-pyrrole

In the title compound, C₂₀H₂₉Br₂NO₈P₂S, the pyrrole ring is essentially planar, with a maximum deviation of 0.013 (3) Å for a C atom. The pyrrole ring is almost orthogonal to the sulfonyl-bound phenyl ring, with a dihedral angle 88.5 (2)°. Both P atoms exhibit distorted tetra­hedral configurations with O—P—O angles widened and O—P—C angles narrowed from the ideal tetra­hedral value. In the crystal, mol­ecules are linked into centrosymmetric dimers via C—H⋯O inter­actions, resulting in R₂²(10) graph-set motifs which are further consolidated by R₂²(13) graph-set ring motifs via C—H⋯O inter­actions, further resulting in chains of mol­ecules running parallel to the c axis; a phosphono O atom is involved in bifurcated hydrogen bonding. All the eth­oxy groups are disordered over two positions each with unequal site-occupancy factors.

Recent advances in the medicinal chemistry of the metabotropic glutamate receptor 1 (mGlu₁)

This Review summarizes the medicinal chemistry found in publications on both orthosteric and allosteric modulators of the metabotropic glutamate receptor 1 (mGlu(1)) from 2005 to the present. The time period covered by the scope of this current review has been particularly rich in mGlu(1)-related publications with numbers quadrupling when compared to the preceding five year period of 2000-2005. Publications in the field peaked in 2007 with over 35 articles appearing in the peer reviewed literature in the course of that year. Given that glutamate is one of the primary excitatory neurotransmitters in the mammalian central nervous system (CNS), it is unsurprising that it acts upon several receptors that are considered to be of potential therapeutic interest for many indications. Orthosteric and allosteric modulation of the receptor is possible, with a logical extrapolation to the chemotypes used for each strategy. The last five years of publications have yielded many mGlu(1) selective antagonist chemotypyes, most of which have shown efficacy in pain in vivo models. However, the primary impact of these compounds has been to highlight the mechanistic safety risks of mGlu(1) antagonism, independent of chemotype. As a review in medicinal chemistry, the primary focus of this paper will be on the design and, to a lesser degree, synthetic strategies for the delivery of subtype selective, CNS penetrant, druglike compounds through a "medchem" program, targeting modulators of the mGlu(1) receptor.

rac-Dimethyl 2-(1H-pyrrole-2-carboxamido)butanedioate

The title compound, C₁₁H₁₄N₂O₅, was synthesized by condensation of (RS)-2-amino­succinic acid dimethyl ester with 2-trichloro­acetyl­pyrrole at room temperature. The amide group is twisted by 7.4 (1)° from the plane of the pyrrole ring. In the crystal, mol­ecules are linked by inter­molecular N—H⋯O hydrogen bonds into chains extending along the c axis.

Methyl 2-(1H-indole-3-carboxamido)acetate

The title compound, C₁₂H₁₂N₂O₃, was synthesized by condensation of methyl amino­acetate with 3-trichloro­acetyl­indole. In the crystal, inter­molecular N—H⋯O hydrogen bonds link the mol­ecules into chains parallel to the b axis. The chains are further connected into a three-dimensional network by N—H⋯O hydrogen bonds involving the indole N atom. In the molecule, the indole skeleton is nearly planar [maximum deviation = 0.012 (1) Å] and the mean plane of the amido group is twisted from the mean plane of indole ring by 17.2 (1)°.

Synthesis and Structure-Activity Relationships of Benzothienothiazepinone Inhibitors of Protein Kinase D

Protein kinase D (PKD) is a member of a novel family of serine/threonine kinases that regulate fundamental cellular processes. PKD is implicated in the pathogenesis of several diseases, including cancer. Progress in understanding the biological functions and therapeutic potential of PKD has been hampered by the lack of specific inhibitors. The benzoxoloazepinolone CID755673 was recently identified as the first potent and selective PKD inhibitor. The study of structure-activity relationships (SAR) of this lead structure led to further improvements in PKD1 potency. We describe herein the synthesis and biological evaluation of novel benzothienothiazepinone analogs. We achieved a ten-fold increase in the in vitro PKD1 inhibitory potency for the second generation lead kb-NB142-70 and accomplished a transition to an almost equally potent novel pyrimidine scaffold, while maintaining excellent target selectivity. These promising results will guide the design of pharmacological tools to dissect PKD function and pave the way for the development of potential anti-cancer agents.

Allosteric modulation of family C G-protein-coupled receptors: from molecular insights to therapeutic perspectives

Allosteric receptor modulation is an attractive concept in drug targeting because it offers important potential advantages over conventional orthosteric agonism or antagonism. Allosteric ligands modulate receptor function by binding to a site distinct from the recognition site for the endogenous agonist. They often have no effect on their own and therefore act only in conjunction with physiological receptor activation. This article reviews the current status of allosteric modulation at family C G-protein coupled receptors in the light of their specific structural features on the one hand and current concepts in receptor theory on the other hand. Family C G-protein-coupled receptors are characterized by a large extracellular domain containing the orthosteric agonist binding site known as the "venus flytrap module" because of its bilobal structure and the dynamics of its activation mechanism. Mutational analysis and chimeric constructs have revealed that allosteric modulators of the calcium-sensing, metabotropic glutamate and GABA(B) receptors bind to the seven transmembrane domain, through which they modify signal transduction after receptor activation. This is in contrast to taste-enhancing molecules, which bind to different parts of sweet and umami receptors. The complexity of interactions between orthosteric and allosteric ligands is revealed by a number of adequate biochemical and electrophysiological assay systems. Many allosteric family C GPCR modulators show in vivo efficacy in behavioral models for a variety of clinical indications. The positive allosteric calcium sensing receptor modulator cinacalcet is the first drug of this type to enter the market and therefore provides proof of principle in humans.

1-Benzyl-N-methyl-1H-pyrrole-2-carboxamide

The asymmetric unit of the title compound, C₁₃H₁₄N₂O, contains two independent mol­ecules, which differ in the twist of the phenyl ring: the N_pyrrole—C(H₂)—C—C torsion angles are −73.0 (3) and 17.1 (3)°. In the crystal structure, mol­ecules are linked through N—H⋯O hydrogen bonds into chains extending along the a axis.

Methyl 3-(1H-indole-3-carboxamido)propionate hemihydrate

The title compound, C₁₃H₁₄N₂O₃·0.5H₂O, was synthesized by the condensation of methyl 3-amino­propionate with 3-trichloro­acetyl­indole. The two organic mol­ecules in the asymmetric unit are both close to planar, with r.m.s. deviations from the best fit plane through all of the non-H atoms of 0.004 (2) Å for mol­ecule A and 0.006 (1) Å for mol­ecule B. Also, the five- and six-membered rings of the indole systems are inclined at 1.67 (8) and 1.50 (8)° in mol­ecules A and B, respectively. In the crystal structure, the organic molecules are connected by inter­molecular N—H⋯O hydrogen bonds, forming chains. O—H⋯O and N—H⋯O hydrogen-bond inter­actions involving the water molecules inter­link these chains, forming double chains approximately parallel to the a axis.

A class of 3S-2-aminoacyltetrahydro-beta-carboline-3-carboxylic acids: their facile synthesis, inhibition for platelet activation, and high in vivo anti-thrombotic potency

3S-Tetrahydro-beta-carboline-3-carboxylic acid (TCCA) effectively inhibits ADP-induced platelet activation. This paper used TCCA as a lead, modified its 2-position with amino acids, and provided 20 novel 3S-2-aminoacyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acids (5a-t). With the in vitro assay, it was demonstrated that this modification diminished the IC(50) values from 701 nM of TCCA to 10 nM of 5a-t. With the in vivo assay, it was demonstrated that this modification reduced the efficacious dose from 5.0 micromol/kg of TCCA to 0.1 micromol/kg of 5a-t. Comparing the Cerius based conformation of them with that of their analogues, the 3-position modified TCCA, it was suggested that the comparatively unfolded conformation was one of the important factors of enhancing the in vivo antithrombotic potency.

Methyl 3-[(1-butyl-1H-indol-3-yl)carbonyl-amino]propionate

In the title mol-ecule, C(17)H(22)N(2)O(3), the mean plane of the terminal (C=O)OMe fragment and the indole plane form a dihedral angle of 78.94 (3)°. Inter-molecular N-H⋯O hydrogen bonds link the mol-ecules into chains extended along the c axis. The crystal packing exhibits π-π inter-actions, indicated by the short distance of 3.472 (2) Å between the centroids of the five-membered heterocycles of neighbouring mol-ecules.

Rapid hit to lead evaluation of pyrazolo[3,4-d]pyrimidin-4-one as selective and orally bioavailable mGluR1 antagonists

Our HTS effort yielded a preferential mGluR1 pyrimidinone antagonist 1 with lead-like characteristics. Rapid hit to lead (HTL) study identified compounds with improved functional activity and selectivity such as 1b with little improvements in ADME properties. Addition of an aminosulfonyl group on the N-1 aromatic ring led to 2f, a compound with similar in vitro biochemical profiles as those of 1b but drastically improved in vitro ADME properties. These improvements were paralleled by rat PK study characterized by low clearance and quantitative bioavailability. Compound 2f represented a true lead-like molecule that is amenable for further lead optimization (LO) evaluation.