Keisuke Aihara

Application of N–C- or C–N-directed sequential native chemical ligation to the preparation of CXCL14 analogs and their biological evaluation

CXCL14 is a chemokine that exhibits chemoattractant activity for activated macrophages, immature dendric cells, natural killer cells, and epithelial tumor cells. Its potential role as a metabolic regulator has recently been disclosed. However, a complete understanding of its physiological roles remains elusive. This is partly due to the lack of appropriate CXCL14-based molecular probes to explore the biological functions of CXCL14. In this context, we have developed synthetic protocols that provide access to a wide variety of CXCL14 analogs. Two sequential native chemical ligation (NCL) protocols, which proceed in opposite directions, have been used to assemble CXCL14 analogs from peptide fragments. The first involved a conventional C-N-directed sequential NCL, and afforded wild-type CXCL14. The other used peptide thioacids in N-C-directed elongation, and yielded CXCL14 analogs with molecular diversity at the C-terminal fragment. The CXCL14 analogs prepared showed biological activity on human monocytic leukemia-derived THP-1 cells that was comparable to that of wild-type CXCL14.

One-Pot/Sequential Native Chemical Ligation Using Photocaged Crypto-thioester

A practical and efficient methodology for the chemical synthesis of peptides/proteins using a one-pot/sequential ligation is described. It features the use of photocleavable S-protection on an N-sulfanylethylaniline moiety. Removal of the S-protecting ligated materials under UV irradiation provides a readily usable mixture for subsequent native chemical ligation.

Identification of SNAIL1 Peptide-Based Irreversible Lysine-Specific Demethylase 1-Selective Inactivators

Inhibition of lysine-specific demethylase 1 (LSD1), a flavin-dependent histone demethylase, has recently emerged as a new strategy for treating cancer and other diseases. LSD1 interacts physically with SNAIL1, a member of the SNAIL/SCRATCH family of transcription factors. This study describes the discovery of SNAIL1 peptide-based inactivators of LSD1. We designed and prepared SNAIL1 peptides bearing a propargyl amine, hydrazine, or phenylcyclopropane moiety. Among them, peptide 3, bearing hydrazine, displayed the most potent LSD1-inhibitory activity in enzyme assays. Kinetic study and mass spectrometric analysis indicated that peptide 3 is a mechanism-based LSD1 inhibitor. Furthermore, peptides 37 and 38, which consist of cell-membrane-permeable oligoarginine conjugated with peptide 3, induced a dose-dependent increase of dimethylated Lys4 of histone H3 in HeLa cells, suggesting that they are likely to exhibit LSD1-inhibitory activity intracellularly. In addition, peptide 37 decreased the viability of HeLa cells. We believe this new approach for targeting LSD1 provides a basis for development of potent selective inhibitors and biological probes for LSD1.

Liquid-Phase Synthesis of Bridged Peptides Using Olefin Metathesis of a Protected Peptide with a Long Aliphatic Chain Anchor

Bridged peptides including stapled peptides are attractive tools for regulating protein-protein interactions (PPIs). An effective synthetic methodology in a heterogeneous system for the preparation of these peptides using olefin metathesis and hydrogenation of protected peptides with a long aliphatic chain anchor is reported.

Stapled BIG3 helical peptide ERAP potentiates anti-tumour activity for breast cancer therapeutics

Estradiol (E2) and the oestrogen receptor-alpha (ERα) signalling pathway play pivotal roles in the proliferative activity of breast cancer cells. Recent findings show that the brefeldin A-inhibited guanine nucleotide-exchange protein 3-prohibitin 2 (BIG3-PHB2) complex plays a crucial role in E2/ERα signalling modulation in breast cancer cells. Moreover, specific inhibition of the BIG3-PHB2 interaction using the ERα activity-regulator synthetic peptide (ERAP: 165–177 amino acids), derived from α-helical BIG3 sequence, resulted in a significant anti-tumour effect. However, the duration of this effect was very short for viable clinical application. We developed the chemically modified ERAP using stapling methods (stapledERAP) to improve the duration of its antitumour effects. The stapledERAP specifically inhibited the BIG3-PHB2 interaction and exhibited long-lasting suppressive activity. Its intracellular localization without the membrane-permeable polyarginine sequence was possible via the formation of a stable α-helix structure by stapling. Tumour bearing-mice treated daily or weekly with stapledERAP effectively prevented the BIG3-PHB2 interaction, leading to complete regression of E2-dependent tumours in vivo. Most importantly, combination of stapledERAP with tamoxifen, fulvestrant, and everolimus caused synergistic inhibitory effects on growth of breast cancer cells. Our findings suggested that the stapled ERAP may be a promising anti-tumour drug to suppress luminal-type breast cancer growth.

Development of an Intein-Inspired Amide Cleavage Chemical Device

A photoresponsive amide cleavage device was developed based on the asparagine imidation-mediated cleavage of peptide bonds during intein-mediated protein splicing. The chemical environment of the protein splicing process was mimicked by the incorporation of geminal dimethyl groups and a secondary amine unit in asparagine scaffold. Furthermore, the resulting photoresponsive device could induce the phototriggered cleavage of an amide bond by the protection of the secondary amine unit with an o-nitrobenzyloxycarbonyl group.

A Recyclable Hydrophobic Anchor-Tagged Asymmetric Amino Thiourea Catalyst

A novel, recyclable, thiourea‐based asymmetric organocatalyst containing a hydrophobic anchor has been developed. The chemical nature of the hydrophobic anchor contributes to the desirable characteristics of the recyclable catalyst. The hydrophobic anchor‐tagged thiourea catalyst is highly soluble in less polar solvents, which is compatible with amino thiourea catalyst‐mediated asymmetric reaction conditions, but sparingly soluble in polar solvents used for the recycle process. This asymmetric catalyst delivers a catalytic performance comparable to that of a parent catalyst and can be readily recycled from reactions.

Facile Preparation of Peptides with C-Terminal N-Alkylamide via Radical-Initiated Dethiocarboxylation

A new synthetic method has been developed to prepare peptides bearing a C-terminal N-alkylamide from peptide thioacids via a radical-initiated dethiocarboxylation process. This method enables the introduction of various alkyl groups to C-terminal amides simply by replacing the amino acid building block. Its application to the preparation of anti-cancer drug ABT-510 is also reported.