Alpha-peptide/beta-sulfonamidopeptide hybrids: analogs of the chemotactic agent for-Met-Leu-Phe-OMe

Rapid Access to Aliphatic Sulfonamides

Herein, we report a mild, rapid, straightforward method for visible-light-mediated sulfonamide ethylation to afford a diverse array of compounds with C(sp³)-sulfonamide skeletons. The method relies on inexpensive, abundant, commercially available primary, secondary, and tertiary alkyl carboxylic acids and alkyl iodides as substrates. The method has a broad substrate scope and potential utility for late-stage functionalization of natural products and synthetic medicines and can be expected to facilitate rapid structural diversification of bioactive molecules.

Synthesis of sulfonopeptides

Sulfonopeptides as the sulfur analogues of natural peptides have been widely used as enzyme inhibitors due to their tetrahedral sulfonamide moiety, which can mimic the transition-state analogues of hydrolysis of the ester and amide bonds. Synthetic methods of sulfonopeptides are reviewed. The synthetic methods of sulfonopeptides include the condensation of N-protected amino acid/peptide acids and 2-aminoalkanesulfonic acids, coupling of N-protected 2-aminoalkanesulfonyl chlorides and amino acid esters/peptide esters, sulfinylation of amino acid esters/peptide esters with N-protected 2-aminoalkanesulfinyl chlorides and subsequent oxidation, the alkylation of taurine-containing peptides, and the displacement of N-aminoacyl/peptidyl 2-aminoalkyl halides/methanesulfonates with sulfites. Hybrid sulfonophosphinopeptides are prepared through the Mannich-type reaction of N-protected 2-aminoalkanesulfonamides/peptidylsulfonamides, aldehydes, and aryldichlorophosphines/phosphorus trichloride followed by the aminolysis with amino acid/peptide esters or hydrolysis. The developed synthetic methods provide diverse synthetic routes for biologically important sulfonopeptides as the candidates of medicinal agents.

γ-AApeptides as a New Strategy for Therapeutic Development

A new class of peptidomimetics termed as "γ-AApeptides" was recently developed by our group. Similar to other peptidomimetics, γ-AApeptides are resistant to proteolytic degradation, and possess limitless potential to introduce chemically diverse functional groups. γ-AApeptides have shown great promise in biomedical applications. In this article, we will review a few examples of γ-AApeptides with biological potential. Certain γ-AApeptides can permeate cell membranes and therefore they can be used as potential drug carrier. γ-AApeptides can also bind to HIV RNA with high specificity and affinity, suggesting their potential application as anti-HIV agents. Moreover, they can mimic host-defense peptides and display potent and broad-spectrum activity towards a range of drug-resistant bacterial pathogens. They are also potential anti-cancer agents. For instance, they have shown great promise in targeted imaging of tumor in mouse model, and they are also capable of disrupting p53/DNA interactions, and thus antagonize STAT3 signaling pathway. Recently, from combinatorial screening, γ-AApeptides are identified to inhibit Aβ peptide aggregation, and thus they can be developed into potential anti- Alzheimer's disease agent.

Peptide-guided functionalization and macrocyclization of bioactive peptidosulfonamides by Pd(II)-catalyzed late-stage C-H activation

Peptides and peptidomimetics are emerging as an important class of clinic therapeutics. Here we report a peptide-guided method for the functionalization and macrocyclization of bioactive peptidosulfonamides by Pd(II)-catalyzed late-stage C-H activation. In this protocol, peptides act as internal directing groups and enable site-selective olefination of benzylsulfonamides and cyclization of benzosulfonamides to yield benzosultam-peptidomimetics. Our results provide an unusual example of benzosulfonamide cyclization with olefins through a sequential C-H activation, which involves the generation of a reactive palladium-peptide complex. Furthermore, this protocol allows facile self-guided macrocyclization of sulfonamide-containing peptides by intramolecular olefination with acrylates and unactivated alkenes, affording bioactive peptidosulfonamide macrocycles of various sizes. Together, our results highlight the utility of peptides as internal directing groups in facilitating transition metal-catalyzed functionalization of peptidomimetics.

γ-AApeptides: Design, Structure, and Applications

The development of sequence-specific peptidomimetics has led to a variety of fascinating discoveries in chemical biology. Many peptidomimetics can mimic primary, secondary, and even tertiary structure of peptides and proteins, and because of their unnatural backbones, they also possess significantly enhanced resistance to enzymatic hydrolysis, improved bioavailability, and chemodiversity. It is known that peptide nucleic acids (PNAs) are peptidic sequences developed for the mimicry of nucleic acids; however, their unique backbone as the molecular scaffold of peptidomimetics to mimic structure and function of bioactive peptides has not been investigated systematically. As such, we recently developed a new class of peptidomimetics, "γ-AApeptides", based on the chiral γ-PNA backbone. They are termed γ-AApeptides because they are the oligomers of γ-substituted-N-acylated-N-aminoethyl amino acids. Similar to other classes of peptidomimetics, γ-AApeptides are also resistant to proteolytic degradation and possess the potential to enhance chemodiversity. Moreover, in our scientific journey on the exploration of this class of peptidomimetics, we have discovered some intriguing structures and functions of γ-AApeptides. In this Account, we summarize the current development and application of γ-AApeptides with biological potential. Briefly, both linear and cyclic (either through head-to-tail or head-to-side-chain cyclization) γ-AApeptides with diverse functional groups can be synthesized easily on the solid phase using the synthetic protocol we developed. γ-AApeptides could mimic the primary structure of peptides, as they project the same number of side chains as peptides of the same lengths. For instance, they could mimic the Tat peptide to permeate cell membranes and bind to HIV RNA with high specificity and affinity. Certain γ-AApeptides show similar activity to the RGD peptide and target integrin specifically on the cell surface. γ-AApeptides with function akin to fMLF peptides are also identified. More importantly, we found that γ-AApeptides can fold into discrete secondary structures, such as helical and β-turn-like structures. Therefore, they could be rationally designed for a range of biological applications. For instance, γ-AApeptides can mimic host-defense peptides and display potent and broad-spectrum activity toward a panel of drug-resistant bacterial pathogens. Meanwhile, because of their stability against proteolysis and their chemodiversity, γ-AApeptides are also amenable for combinatorial screening. We demonstrate that, through combinatorial selection, certain γ-AApeptides are identified to inhibit Aβ40 peptide aggregation, suggesting their potential use as a molecular probe to intervene in Alzheimer's disease. In addition, a few γ-AApeptides identified from the γ-AApeptide library have been shown to bind to the DNA-binding domain of STAT3 and antagonize STAT3/DNA interactions. Our studies suggest that, with further studies and exploration on both structures and functions, γ-AApeptides may emerge to be a new class of peptidomimetics that play an important role in chemical biology and biomedical sciences.

Design, synthesis and characterization of fMLF-mimicking AApeptides

The tripeptide N-formyl-Met-Leu-Phe (fMLF) is a potent neutrophil chemoattractant and the reference agonist for the G protein-coupled N-formylpeptide receptor (FPR). As it plays a very important role in host defense and inflammation, there has been considerable interest in the development of fMLF analogues in the hope of identifying potential therapeutic agents. Herein we report the design, synthesis, and evaluation of AApeptides that mimic the structure and function of fMLF. The lead AApeptides induced calcium mobilization and mitogen-activated protein kinase (MAPK) signal transduction pathways in FPR-transfected rat basophilic leukemic (RBL) cells. More intriguingly, at high concentrations, certain AApeptides were more effective than fMLF in the induction of calcium mobilization. Their agonistic activity is further supported by their ability to stimulate chemotaxis and the production of superoxide in HL-60 cells. Similarly to fMLF, these AApeptides are much more selective towards FPR1 than FPR2. These results suggest that the fMLF-mimicking AApeptides might emerge as a new class of therapeutic agents that target FPRs.

Synthesis and activity of endomorphin-2 and morphiceptin analogues with proline surrogates in position 2

The opioid agonists endomorphins (Tyr-Pro-Trp-Phe-NH(2); EM1 and Tyr-Pro-Phe-Phe-NH(2); EM2) and morphiceptin (Tyr-Pro-Phe-Pro-NH(2)) exhibit an extremely high selectivity for mu-opioid receptor. Here a series of novel EM2 and morphiceptin analogues containing in place of the proline at position 2 the S and R residues of beta-homologues of proline (HPro), of 2-pyrrolidinemethanesulphonic acid (HPrs) and of 3-pyrrolidinesulphonic acid (betaPrs) have been synthesized and their binding affinity and functional activity have been investigated. The highest micro-receptor affinity is shown by [(S)betaPrs(2)]EM2 analogue (6e) which represents the first example of a beta-sulphonamido analogue in the field of opioid peptides.