Structure-based design and synthesis of C-1- and C-4-modified analogs of zanamivir as neuraminidase inhibitors.

In order to exploit the 430-cavity in the active sites of neuraminidases, 22 zanamivir analogs with C-1 and C-4 modification were synthesized, and their inhibitory activities against both group-1 (H5N1, H1N1) and group-2 neuraminidases (H3N2) were determined. Compound 9f exerts the most potency, with IC(50) value of 0.013, 0.001, and 0.09 µM against H3N2, H5N1, and H1N1, which is similar to that of zanamivir (H3N2 IC(50) = 0.0014 µM, H5N1 IC(50) = 0.012 µM, H1N1 IC(50) = 0.001 µM). Pharmacokinetic studies of compound 9f in rats showed a much longer plasma half-life (t(1/2)) than that of zanamivir following administration (po dose). Molecular modeling provided information about the binding model between the new inhibitors and neuraminidase, with the elongated groups at the C-1-position being projected toward the 430-loop region. This study may represent a novel starting point for the future development of improved antiflu agents.

Development of a novel class of B-Raf(V600E)-selective inhibitors through virtual screening and hierarchical hit optimization.

Oncogenic mutations in critical nodes of cellular signaling pathways have been associated with tumorigenesis and progression. The B-Raf protein kinase, a key hub in the canonical MAPK signaling cascade, is mutated in a broad range of human cancers and especially in malignant melanoma. The most prevalent B-Raf(V600E) mutant exhibits elevated kinase activity and results in constitutive activation of the MAPK pathway, thus making it a promising drug target for cancer therapy. Herein, we describe the development of novel B-Raf(V600E) selective inhibitors via multi-step virtual screening and hierarchical hit optimization. Nine hit compounds with low micromolar IC(50) values were identified as B-Raf(V600E) inhibitors through virtual screening. Subsequent scaffold-based analogue searching and medicinal chemistry efforts significantly improved both the inhibitor potency and oncogene selectivity. In particular, compounds 22f and 22q possess nanomolar IC(50) values with selectivity for B-Raf(V600E)in vitro and exclusive cytotoxicity against B-Raf(V600E) harboring cancer cells.

Recent advances in neuraminidase inhibitor development as anti-influenza drugs.

The recent emergence of the highly pathogenic H5N1 subtype of avian influenza virus (AIV) and of the new type of human influenza A (H1N1) have emphasized the need for the development of effective anti-influenza drugs. Presently, neuraminidase (NA) inhibitors are widely used in the treatment and prophylaxis of human influenza virus infection, and tremendous efforts have been made to develop more potent NA inhibitors to combat resistance and new influenza viruses. In this review, we discuss the structural characteristics of NA catalytic domains and the recent developments of new NA inhibitors using structure-based drug design strategies. These drugs include analogues of zanamivir, analogues of oseltamivir, analogues of peramivir, and analogues of aromatic carboxylic acid and present promising options for therapeutics or leads for further development of NA inhibitors that may be useful in the event of a future influenza pandemic.

Synthesis of C-4-modified zanamivir analogs as neuraminidase inhibitors and their anti-AIV activities.

With the introduction of bioisosteres of the guanidinium group together with scaffold hopping, 35 zanamivir analogs with C-4-modification were synthesized, and their inhibitory activities against both group-1 and group-2 neuraminidase (H5N1 and H3N2) were determined. Compound D26 exerts the most potency, with IC(50) values of 0.58 and 2.72 µM against N2 and N1, respectively. Further preliminary anti-avian influenza virus (AIV, H5N1) activities against infected MDCK cells were evaluated, and D5 exerts ∼58% protective against AIV infection, which was comparable to zanamivir (∼67%). In a rat pharmacokinetic study, compound D5 showed an increased plasma half-life (t(1/2)) compared to zanamivir following either intravenous or oral administration. This study may represent a new start point for the future development of improved anti-AIV agents.

Structural and functional analysis of laninamivir and its octanoate prodrug reveals group specific mechanisms for influenza NA inhibition.

The 2009 H1N1 influenza pandemic (pH1N1) led to record sales of neuraminidase (NA) inhibitors, which has contributed significantly to the recent increase in oseltamivir-resistant viruses. Therefore, development and careful evaluation of novel NA inhibitors is of great interest. Recently, a highly potent NA inhibitor, laninamivir, has been approved for use in Japan. Laninamivir is effective using a single inhaled dose via its octanoate prodrug (CS-8958) and has been demonstrated to be effective against oseltamivir-resistant NA in vitro. However, effectiveness of laninamivir octanoate prodrug against oseltamivir-resistant influenza infection in adults has not been demonstrated. NA is classified into 2 groups based upon phylogenetic analysis and it is becoming clear that each group has some distinct structural features. Recently, we found that pH1N1 N1 NA (p09N1) is an atypical group 1 NA with some group 2-like features in its active site (lack of a 150-cavity). Furthermore, it has been reported that certain oseltamivir-resistant substitutions in the NA active site are group 1 specific. In order to comprehensively evaluate the effectiveness of laninamivir, we utilized recombinant N5 (typical group 1), p09N1 (atypical group 1) and N2 from the 1957 pandemic H2N2 (p57N2) (typical group 2) to carry out in vitro inhibition assays. We found that laninamivir and its octanoate prodrug display group specific preferences to different influenza NAs and provide the structural basis of their specific action based upon their novel complex crystal structures. Our results indicate that laninamivir and zanamivir are more effective against group 1 NA with a 150-cavity than group 2 NA with no 150-cavity. Furthermore, we have found that the laninamivir octanoate prodrug has a unique binding mode in p09N1 that is different from that of group 2 p57N2, but with some similarities to NA-oseltamivir binding, which provides additional insight into group specific differences of oseltamivir binding and resistance.

Design and synthesis of small molecule RhoA inhibitors: a new promising therapy for cardiovascular diseases?

RhoA is a member of Rho GTPases, a subgroup of the Ras superfamily of small GTP-binding proteins. RhoA, as an important regulator of diverse cellular signaling pathways, plays significant roles in cytoskeletal organization, transcription, and cell-cycle progression. The RhoA/ROCK inhibitors have emerged as a new promising treatment for cardiovascular diseases. However, to date, RhoA inhibitors are macromolecules, and to our knowledge, small molecular-based inhibitors have not been reported. In this study, a series of first-in-class small molecular RhoA inhibitors have been discovered by using structure-based virtual screening in conjunction with chemical synthesis and bioassay. Virtual screening of ∼200,000 compounds, followed by SPR-based binding affinity assays resulted in three compounds with binding affinities to RhoA at the micromolar level (compounds 1-3). Compound 1 was selected for further structure modifications in considering binding activity and synthesis ease. Fourty-one new compounds (1, 12a-v, 13a-h, and 14a-j) were designed and synthesized accordingly. It was found that eight (12a, 12j, 14a, 14b, 14d, 14e, 14 g, and 14h) showed high RhoA inhibition activities with IC(50) values of 1.24 to 3.00 µM. A pharmacological assay indicated that two compounds (14g and 14 h) demonstrated noticeable vasorelaxation effects against PE-induced contraction in thoracic aorta artery rings and served as good leads for developing more potent cardiovascular agents.

A nonproton ligand sensor in the acid-sensing ion channel.

Acid-sensing ion channels (ASICs) have long been considered as extracellular proton (H(+))-gated cation channels, and peripheral ASIC3 channels seem to be a natural sensor of acidic pain. Here, we report the identification of a nonproton sensor on ASIC3. We show first that 2-guanidine-4-methylquinazoline (GMQ) causes persistent ASIC3 channel activation at the normal pH. Using GMQ as a probe and combining mutagenesis and covalent modification analysis, we then uncovered a ligand sensor lined by residues around E423 and E79 of the extracellular "palm" domain of the ASIC3 channel that is crucial for activation by nonproton activators. Furthermore, we show that GMQ activates sensory neurons and causes pain-related behaviors in an ASIC3-dependent manner, indicating the functional significance of ASIC activation by nonproton ligands. Thus, natural ligands beyond protons may activate ASICs under physiological and pathological conditions through the nonproton ligand sensor, serving for channel activation independent of abrupt and marked acidosis.

The 2009 pandemic H1N1 neuraminidase N1 lacks the 150-cavity in its active site.

Influenza A virus neuraminidase can be classified into groups 1 and 2 on the basis of its primary structure. The main structural feature of group 1 neuraminidase is an extra cavity in the active site, the 150-cavity. Here we present the crystal structure of neuraminidase from the 2009 pandemic H1N1 influenza strain. In contrast to other characterized N1 neuraminidases, which are all members of group 1, 2009 H1N1 neuraminidase does not have a 150-cavity.

Regioselective synthesis of 3-benzazepinones and unexpected 5-bromo-3-benzazepinones.

A regioselective hydroamidation of 2-(1-alkynyl)phenylacetamides with Au(PPh(3))Cl/AgSbF(6) as the catalyst proceeded by a 7-endo-dig pathway to afford 3-benzazepinones. This method accommodates a broad range of alkyl and aryl alkynyl substitutes in moderate to high yields (63-91%). Moreover, unexpectedly, we also discovered a gold-mediated transformation from 2-(1-alkynyl)phenylacetamides to 5-bromo-3-benzazepinones, and AuBr(3) was found to not only play an activation role but also act as a reactant in the reaction for the first time.

Highly alpha-selective synthesis of sialyl spirohydantoins by regiospecific domino condensation/O-->N acyl migration/N-sialylation of carbodiimides with peracetylated sialic acid.

A novel and efficient process for the synthesis of alpha-sialyl spirohydantoin analogues via one-pot sequential reaction involving various carbodiimides and peracetylated Neu5Ac is reported. BF(3) x Et(2)O mediating intramolecular N-sialylation with excellent alpha-selectivity is first demonstrated.

Gold(I)-catalyzed tandem transformation: a simple approach for the synthesis of pyrrolo/pyrido[2,1-a][1,3]benzoxazinones and pyrrolo/pyrido[2,1-a]quinazolinones.

We have developed a simple method for the synthesis of pyrrolo/pyrido[2,1-a][1,3]benzoxazinones and pyrrolo/pyrido[2,1-a]quinazolinones from 2-amino benzoic acids and 2-amino benzamides via a gold(I)-catalyzed tandem coupling/cyclization process. The tricyclic or polycyclic molecular architectures were constructed in one pot with the formation of three new bonds.

Metal-free synthesis of 2-substituted (N, O, C) benzothiazoles via an intramolecular C-S bond formation.

An efficient, economical, and convenient method was developed for the preparation of 2-substituted (N, O, C) benzothiazoles from N'-substituted-N-(2-halophenyl)thioureas, O'-substituted-N-(2-halophenyl) carbamothioates, or N-(2-halophenyl) thioamides via a base-promoted cyclization in dioxane without any transition metal. A one-pot variant combining the synthesis of the thiourea and the cyclization was also demonstrated. High yields were obtained, and a variety of functional groups were tolerated under these conditions. Transition-metal-free, mild reactive conditions, wide application scope, and shorter reaction times make this method superior to the reported methods for the synthesis of 2-substituted benzothiazoles and suitable for combinatorial format.

Gold-catalyzed one-pot cascade construction of highly functionalized pyrrolo[1,2-a]quinolin-1(2H)-ones.

An efficient protocol was developed for the synthesis of fused heterocyclic multiring compounds pyrrolo[1,2-a]quinolin-1(2H)-ones via a AuBr(3)/AgSbF(6)-catalyzed cascade transformation. Significantly, the strategy affords a straightforward and efficient approach to construction of tricyclic lactam molecular architectures in which two new C-C bonds and one new C-N bond are formed in a one-pot synthetic operation from simple starting materials. Moreover, a broad spectrum of substrates can participate in the process effectively to produce the desired products in good yields and with excellent regio- and chemoselectivities.

Copper(I)-catalyzed one-pot synthesis of 2H-1,4-benzoxazin-3-(4H)-ones from o-halophenols and 2-chloroacetamides.

We developed an efficient and convenient method for preparing N-substituted 2H-1,4-benzoxazin-3-(4H)-ones from 2-halophenols via a nucleophilic substitution with 2-chloroacetamides followed by a CuI-catalyzed coupling cyclization. A broad spectrum of substrates can be effectively employed to afford the desired products in good yields. Since this method involves simple reaction conditions, a short reaction time, and a broad substrate scope, it is particularly attractive for the efficient preparation of biologically and medicinally interesting molecules.

Efficient dehydrative sialylation of C-4-aminated sialyl-hemiketal donors with Ph2SO/Tf2O.

An efficient approach to the dehydrative sialylation of various substrates with C-4-aminated sialyl-hemiketal donors by using the reagent combination of diphenyl sulfoxide and triflic anhydride is reported. By using a C-4-hindered non-nucleophilic amine auxiliary, excellent yields and high alpha-stereoselectivities were obtained for coupling with a wide range of primary and secondary acceptors.