Ac4GlcNAcF3, an OGT-tolerated but OGA-resistant regulator for O-GlcNAcylation.

O-Linked N-acetylglucosamine (O-GlcNAc) is an abundant posttranslationalmonosaccaride-modification found on Ser or Thr residues of intracellular proteins in most eukaryotes. The dynamic nature of O-GlcNAc has enabled researchers to modulate the stoichiometry of O-GlcNAc on proteins in order to investigate its function. Cell permeable small moleculars have proven invaluable tools to increase O-GlcNAc levels. Herein, using in vitro substrate screening, we identified GlcNAcF3 as an OGT-accepted but OGA-resistant sugar mimic. Cellular experiments with cell-permeable peracetylated-GlcNAcF3 (Ac4GlcNAcF3) displayed that Ac4GlcNAcF3 was a potent tool to increase O-GlcNAc levels in several cell lines. Further, NIH3T3 cells interfered with OGT (siOGT) showed significant decreasing of O-GlcNAc levels with Ac4GlcNAcF3 treatment, indicating O-GlcNAcF3 was an OGT-dependent modification. In addition, cellular toxic assay confirmed O-GlcNAcF3 production has no significant effect on cell proliferation or viability. Thus, Ac4GlcNAcF3 represents a safe and dual regulator for both OGT and OGA, which will benefit the study of O-GlcNAc.

Synthesis and biological evaluation of N-arylated-lactam-type iminosugars as potential immunosuppressive agents.

Since the immunosuppressive agents currently used in clinics have significant side effects, it is very important to search for new effective and safe immunosuppressants. Iminosugars as a new class of immunosuppressants are less explored. In this report, 24 new N-arylated iminosugar derivatives, including d-talo and d-galacto epimers, were designed and synthesized, and their immunosuppressive effects were evaluated by MTT assay. The experimental data demonstrated that compound 20 showed the strongest inhibition effect (IC50 = 6.94 µM). Further studies revealed that the inhibitory effects on splenocyte proliferation may come from the suppression of both IFN-γ and IL-4 cytokines. The preliminary structure-activity relationship (SAR) analysis suggested that N-arylated d-galacto-type iminosugars showed better inhibitory activities than d-talo-type analogues. The SAR analysis also showed that the inhibition effect of iminosugars can be improved by decreasing the polarity or increasing the hydrophobicity. These results may be beneficial to the discovery of new iminosugar derivatives as immunosuppressive agents.

Indolo-quinoline boron difluoride dyes: synthesis and spectroscopic properties.

Novel indolo-quinoline compounds were efficiently prepared via a Povarov-type reaction, and the structures were further modified by a Suzuki coupling reaction. The corresponding BF2-rigidified complexes were prepared and their spectroscopic properties were characterized with large Stokes shifts (up to 211 nm) and up to near-infrared (NIR) wavelength (667 nm). The synthetic complexes could be used as new fluorescent dyes.

A new GLP-1 analogue with prolonged glucose-lowering activity in vivo via backbone-based modification at the N-terminus.

Glucagon-like peptide-1 (GLP-1) is an endogenous insulinotropic hormone with wonderful glucose-lowering activity. However, its clinical use in type II diabetes is limited due to its rapid degradation at the N-terminus by dipeptidyl peptidase IV (DPP-IV). Among the N-terminal modifications of GLP-1, backbone-based modification was rarely reported. Herein, we employed two backbone-based strategies to modify the N-terminus of tGLP-1. Firstly, the amide N-methylated analogues 2-6 were designed and synthesized to make a full screening of the N-terminal amide bonds, and the loss of GLP-1 receptor (GLP-1R) activation indicated the importance of amide H-bonds. Secondly, with retaining the N-terminal amide H-bonds, the ß-peptide replacement strategy was used and analogues 7-13 were synthesized. By two rounds of screening, analogue 10 was identified. Analogue 10 greatly improved the DPP-IV resistance with maintaining good GLP-1R activation in vitro, and showed approximately a 4-fold prolonged blood glucose-lowering activity in vivo in comparison with tGLP-1. This modification strategy will benefit the development of GLP-1-based anti-diabetic drugs.

Crystal engineering of an nbo topology metal-organic framework for chemical fixation of CO2 under ambient conditions.

Crystal engineering of the nbo metal-organic framework (MOF) platform MOF-505 with a custom-designed azamacrocycle ligand (1,4,7,10-tetrazazcyclododecane-N,N',N'',N'''-tetra-p-methylbenzoic acid) leads to a high density of well-oriented Lewis active sites within the cuboctahedral cage in MMCF-2, [Cu2(Cu-tactmb)(H2O)3(NO3)2]. This MOF demonstrates high catalytic activity for the chemical fixation of CO2 into cyclic carbonates at room temperature under 1 atm pressure.

AApeptides as a new class of antimicrobial agents.

Antibiotic resistance is an increasing public health concern around the world, and is recognized as one of the greatest threats facing humankind in the 21(st) century. Natural antimicrobial peptides (AMPs) are small cationic amphiphilic peptides found in virtually all living organisms, and play a key role in the defense against bacterial infections. Compared with conventional antibiotics, which target specific metabolic processes, AMPs are able to adopt globally amphipathic conformations, and kill bacteria through disruption of their membranes. As such, AMPs do not readily induce drug-resistance. However, AMPs are associated with intrinsic drawbacks such as low-to-moderate activity, susceptibility to enzymatic degradation, and inconvenience for optimization. Recently, we have developed a new class of peptidomimetics termed "AApeptides". Such peptide mimics are highly resistant to protease degradation and are straightforward for chemical diversification and development. Our current studies show that AApeptides with globally amphipathic structures can mimic the bactericidal mechanism of AMPs, and display potent and broad-spectrum activity against both Gram-positive and -negative multi-drug-resistant bacteria. In this review, we summarize our current findings of antimicrobial AApeptides, and discuss potential future directions on the development of more potent and specific analogues.

Cellular translocation of a γ-AApeptide mimetic of Tat peptide.

Cell-penetrating peptides including the trans-activating transcriptional activator (Tat) from HIV-1 have been used as carriers for intracellular delivery of a myriad of cargoes including drugs, molecular probes, DNAs and nanoparticles. Utilizing fluorescence flow cytometry and confocal fluorescence microscopy, we demonstrate that a γ-AApeptide mimetic of Tat (48-57) can cross the cell membranes and enter the cytoplasm and nucleus of cells, with efficiency comparable to or better than that of Tat peptide (48-57). Deletion of the four side chains of the γ-AApeptide attenuates translocation capability. We also establish that the γ-AApeptide is even less toxic than the Tat peptide against mammalian cells. In addition to their low toxicity, γ-AApeptides are resistant to protease degradation, which may prove to be advantageous over α-peptides for further development of molecular transporters for intracellular delivery.

Cellular uptake of an α-AApeptide.

Some short and cationic peptides such as the Tat peptide can cross the cell membrane and function as vectors for intracellular delivery. Here we show that an α-AApeptide is able to penetrate the membranes of living cells from an extracellular environment and enter the endosome and cytoplasm of cells. The efficiency of the cellular uptake is comparable to a Tat peptide (48-57) of the same length and is unexpectedly superior to an α-peptide with identical functional groups. The mechanism of uptake is similar to that of the Tat peptide and is through endocytosis by an energy-dependent pathway. Due to the easy synthesis of the α-AApeptides, their resistance to proteolytic hydrolysis, and their low cytotoxicity, α-AApeptides represent a new class of transporters for the delivery of drugs.

Design, synthesis, and bioassay of 5-epi-aminoglycosides.

For the purpose of seeking new antibiotics, researchers usually modify the already-existing ones. However, this strategy has been extensively used and is close to its limits, especially in the case of aminoglycosides, and it is difficult to find a proper aminoglycoside antibiotic for novel modification. In this paper, we reported the design, synthesis, and evaluation of a series of 5-epi-neamine derivatives based on the structural information of bacterial 16S RNA A-site binding with aminoglycosides. Bioassay results showed that our design strategy was feasible. Our study offers a new way to search for structurally novel aminoglycosides. Meanwhile, our study provides valuable structure-activity relationship information, which will lead to better understanding and exploitation of the drug target, and improved development of new aminoglycoside antibiotics.

γ-AApeptides bind to RNA by mimicking RNA-binding proteins.

The interactions between proteins and RNAs are of vital importance for many cellular processes, including transcription and processing of RNA, translation, and viral infections. Here we report an γ-AApeptide that can mimic HIV-1 Tat protein and bind to TAR RNAs of HIV and BIV with nanomolar affinity, comparable to that of the RNA-binding fragment of Tat (amino acids 49-58). The interaction is resistant to the presence of a large excess of tRNA. With resistance to proteolytic hydrolysis and limitless potential for diversification, γ-AApeptides may emerge as a new class of peptidomimetics to modulate RNA-protein interactions.

Synthesis and biological evaluation of bergenin derivatives as new immunosuppressants.

Bergenin, which is isolated from Bergenia species, exhibits various pharmacological properties. In the search for new types of immunosuppressants, a series of bergenin derivatives were designed and synthesized, and their immunosuppressive effects were evaluated by the CCK-8 assay. The experimental data demonstrated that compounds 7 and 13 showed the strongest inhibition effects on mouse splenocyte proliferation (IC50 = 3.52 and 5.39 µM, respectively). Further studies revealed that the inhibitory effect may come from the suppression of both IFN-γ and IL-4 cytokines. Alkylated derivatives of bergenin with n-hexyl and n-heptyl on the two phenolic hydroxyl groups showed better inhibitory activities. The hydrophobicity of bergenin derivatives, the configuration of the 4-OH in bergenin, and the ability to form hydrogen bonds of the substituents on the C-4 position are important to the immunosuppressive activity. This work proved that the modifications of bergenin may represent a new route to the discovery of a new class of immunosuppressive agents.

Synthesis of N-Substituted Iminosugar Derivatives and Evaluation of Their Immunosuppressive Activities.

It is important to find more effective and safer immunosuppressants, because clinically used immunosuppressive agents have significant side effects. A series of N-substituted iminosugar derivatives were designed and synthesized, and their immunosuppressive effects were evaluated by the CCK-8 assay. The results revealed that iminosugars 10 e and 10 i, that is, (3R,4S)-1-(4-heptyloxylphenylethyl)pyrrolidine-3,4-diol and (3R,4S)-1-[2-(2-chloro-4-(p-tolylthio)-phenyl-1-yl)ethyl]pyrrolidine-3,4-diol, respectively, exhibited the strongest inhibitory effects on mouse splenocyte proliferation (IC50 =2.16 and 2.48 µm, respectively), whereas the iminosugars containing an amide group near the hydrophilic head (compounds 10 j-n) exhibited no inhibitory effects. Further studies revealed that the inhibitory effects on splenocyte proliferation may have come from the suppression of both IFN-γ and IL-4 cytokines. Our results suggest that synthetic iminosugars, especially compounds 10 e and 10 i, hold potential as immunosuppressive agents.

Rational Design of Dimeric Lysine N-Alkylamides as Potent and Broad-Spectrum Antibacterial Agents.

Antibiotic resistance is one of the biggest threats to public health, and new antibacterial agents hence are in an urgent need to combat infectious diseases caused by multidrug-resistant (MDR) pathogens. Utilizing dimerization strategy, we rationally designed and efficiently synthesized a new series of small molecule dimeric lysine alkylamides as mimics of AMPs. Evaluation of these mimics against a panel of Gram-positive and Gram-negative bacteria including MDR strains was performed, and a broad-spectrum and potent compound 3d was identified. This compound displayed high specificity toward bacteria over mammalian cell. Time-kill kinetics and mechanistic studies suggest that compound 3d quickly eliminated bacteria in a bactericidal mode by disrupting bacterial cell membrane. In addition, lead compound 3d could inhibit biofilm formation and did not develop drug resistance in S. aureus and E. coli over 14 passages. These results suggested that dimeric lysine nonylamide has immense potential as a new type of novel small molecular agent to combat antibiotic resistance.

General Approach to Five-Membered Nitrogen Heteroaryl C-Glycosides Using a Palladium/Copper Cocatalyzed C-H Functionalization Strategy.

A general approach to the synthesis of diverse heteroaryl-C-Δ1,2-glycosides has been developed by employing the Pd(OAc)2/CuI cocatalyzed direct cross-coupling of five-membered nitrogen heterocycles with 1-iodoglycals in a C-H activation manner. Using this method, 27 examples of heteroaryl-C-Δ1,2-glycosides, containing indoles, thiazoles, benzothiazoles, imidazoles, benzimidazoles, and benzoxazoles as aglycones were obtained in 43-99% yield.

Ligand-Controlled Monoselective C-Aryl Glycoside Synthesis via Palladium-Catalyzed C-H Functionalization of N-Quinolyl Benzamides with 1-Iodoglycals.

A monoselective synthesis of aryl-C-Δ(1,2)-glycosides from 1-iodoglycals via palladium-catalyzed ortho-C-H activation of N-quinolyl benzamides has been developed. An amino acid derivative was used as a crucial ligand to improve the yield and monoselectivity of the coupling reaction. The utility of this protocol was demonstrated by a concise synthesis of key moieties of some natural products.

Highly Substituted Cyclopentane-CMP Conjugates as Potent Sialyltransferase Inhibitors.

Sialylconjugates on cell surfaces are involved in many biological events such as cellular recognition, signal transduction, and immune response. It has been reported that aberrant sialylation at the nonreducing end of glycoconjugates and overexpression of sialyltransferases (STs) in cells are correlated with the malignance, invasion, and metastasis of tumors. Therefore, inhibitors of STs would provide valuable leads for the discovery of antitumor drugs. On the basis of the transition state of the enzyme-catalyzed sialylation reaction, we proposed that the cyclopentane skeleton in its two puckered conformations might mimic the planar structure of the donor (CMP-Neu5Ac) in the transition state. A series of cyclopentane-containing compounds were designed and synthesized by coupling different cyclopentane α-hydroxyphosphonates with cytidine phosphoramidite. Their inhibitory activities against recombinant human ST6Gal-I were assayed, and a potent inhibitor 48l with a Ki of 0.028 ± 0.006 µM was identified. The results show that the cyclopentanoid-type compounds could become a new type of sialyltransferase inhibitors as biological probes or drug leads.

γ-AApeptide-based small-molecule ligands that inhibit Aß aggregation.

We report the design, synthesis, characterization and evaluation of a novel class of γ-AApeptide one-bead-one-compound (OBOC) library, from which a small γ-AApeptide was identified to effectively prevent and disassemble Aß aggregation.

Synthesis of AApeptides.

The creation and development of nonnatural peptidomimetics has become an area of increasing significance in bioorganic and chemical biology. A wide range of new peptide mimics with novel structures and functions are urgently needed to be explored in order to identify potential drug candidates and targeted probes, and to study protein functions. AApeptides are a new class of peptide mimics based on chiral PNA backbone. They are resistant to proteolytic degradation and have limitless potential for diversification. They have been found to have a wide variety of biological applications including cellular translocation, disruption of protein-protein interactions, formation of nanostructures, antimicrobial activity, etc. The synthesis of AApeptides is modular and straightforward. In this chapter, methods for the synthesis of AApeptides (including different subclasses) are described.

Polymyxin derivatives: a patent evaluation (WO2012168820).

The patent application WO201268820 claims a new class of polymyxin derivatives with potent antibacterial activity, especially toward Gram-negative pathogens. Compared to parent polymyxin B (PMB), the new derivatives have more potent antibacterial activity, as well as reduced cytotoxicity against human renal cells.

Recent development of small antimicrobial peptidomimetics.

Antimicrobial peptides (AMPs) hold promise to circumvent the emergence of drug resistance occurring in the treatment of bacteria using many conventional antibiotics. Antimicrobial peptidomimetics, which mimic bactericidal mechanisms of AMPs, may overcome the disadvantages of AMPs and become the new generation of antibiotic therapeutics. In this review, some recent examples in the development of antimicrobial peptidomimetics are highlighted. The potential of antimicrobial agents has been demonstrated for therapeutic uses. Meanwhile, perspectives on their further development and applications are also presented.