General Description

Fmoc-N-Me-Arg(pbf)-OH, a versatile building block, finds applications in solid-phase peptide synthesis for bioorthogonal conjugation, PET imaging of NTS1-positive tumors, and synthesizing peptide antagonists targeting α4β7 integrin. It enables efficient peptide labeling, selective tumor imaging with high affinity and stability, and precise synthesis of antagonists with enhanced properties. The compound's compatibility with Fmoc-strategy synthesis, bioorthogonality, and ability to facilitate diverse peptide modifications make it a valuable tool in research and therapeutic contexts. Overall, Fmoc-N-Me-Arg(pbf)-OH shows significant potential in advancing peptide chemistry for various biological applications, including imaging and drug discovery.

Figure 1. Fmoc-N-Me-Arg(pbf)-OH

Applications in Solid-Phase Synthesis

Fmoc-N-Me-Arg(pbf)-OH, an alkyne-functionalized arginine derivative, represents a significant advancement in solid-phase peptide synthesis, particularly for enabling "bioorthogonal" peptide conjugation. Traditionally, amino-functionalized Nω-carbamoylated arginines have been utilized as arginine surrogates for peptide labeling. However, this method faces limitations when peptides also contain lysine or cysteine residues. This novel building block overcomes such challenges by offering compatibility with Fmoc-strategy solid-phase peptide synthesis. The incorporation of the alkynylated arginine into various peptides, including biologically active linear hexapeptides and cyclic pentapeptides, has been demonstrated successfully. One of the key applications of Fmoc-N-Me-Arg(pbf)-OH lies in facilitating peptide conjugation to azido-functionalized fluorescent dyes through "click" chemistry. This process allows for efficient and selective labeling of peptides, enhancing their utility in various biological applications. Notably, the "bioorthogonal" nature of this approach enables peptide conjugation even in the presence of lysine residues within the peptide sequence. This feature ensures minimal interference with biological systems, making Fmoc-N-Me-Arg(pbf)-OH a valuable tool for peptide modification and functionalization in both research and therapeutic contexts. ¹

Applications in PET Imaging of Tumors

Fmoc-N-Me-Arg(pbf)-OH, a derivative of neurotensin (NT) analogs, has emerged as a promising agent for positron emission tomography (PET) imaging of NTS1-positive tumors. Neurotensin receptors of subtype-1 (NTS1) are abundantly expressed in various malignant tumors, including pancreatic adenocarcinoma, colorectal, and prostate carcinoma, making them attractive targets for tumor imaging and therapy. In previous approaches, NT peptide analogs used for PET imaging were modified and extended at the N-terminus. However, in this study, researchers focused on modifying specific arginine residues, namely Arg8 or Arg9, through Nω-carbamoylation and subsequent fluoroglycosylation. This strategy proved effective in developing NT analogs with high affinity for NTS1 receptors, retaining affinity in the one-digit nanomolar range and exhibiting high metabolic stability in vitro. The radioligand [18F]Nα-methyl-(Nω-{N-[4-(3-{1-[6-deoxy-6-fluoro-β-D-glucopyranosyl]-1H-1,2,3-triazol-4 -yl}propanoyl)aminobutyl]aminocarbonyl})Arg-Arg-Pro-Tyr-2-tert-butyl-Gly-Leu-OH tris(hydrotrifluoroacetate) demonstrated promising biokinetics in tumor-bearing mice. Fmoc-N-Me-Arg(pbf)-OH exhibited high tumor uptake and retention, predominantly renal clearance, and rapid wash-out from non-target tissues and blood. Overall, Fmoc-N-Me-Arg(pbf)-OH holds significant potential as a molecular probe for PET imaging of NTS1-expressing tumors. Its high affinity, metabolic stability, and favorable biokinetics make it a promising candidate for further development in tumor imaging and potentially for targeted therapy. ²

Applications in Synthesizing Peptide Antagonists

Fmoc-N-Me-Arg(pbf)-OH plays a crucial role in synthesizing peptide antagonists targeting α4β7 integrin. The methods involve both solid-phase and solution-phase approaches, as well as the condensation of smaller peptide fragments. One significant aspect is the incorporation of penicillamine residues into the peptide sequences, which enhances their antagonist properties. The synthesis of α4β7 peptide antagonists by Fmoc-N-Me-Arg(pbf)-OH typically includes steps such as cyclization to form disulfide bonds and conjugation of peptide dimers via linkers. In particular, a invention provides methods for synthesizing both monomeric and dimeric peptide antagonists with precise control over their structure and functionality. Additionally, the invention encompasses the use of pseudoproline penicillamine derivatives in peptide synthesis, further expanding the scope of potential antagonists that can be generated. Overall, Fmoc-N-Me-Arg(pbf)-OH enables the efficient and versatile synthesis of α4β7 peptide antagonists, offering promising opportunities for drug discovery and development in the field of integrin-targeted therapies. ³

Reference

1. Spinnler K, von Krüchten L, Konieczny A, Schindler L, Bernhardt G, Keller M. An Alkyne-functionalized Arginine for Solid-Phase Synthesis Enabling "Bioorthogonal" Peptide Conjugation. ACS Med Chem Lett. 2019; 11(3): 334-339.

2. Schindler L, Wohlfahrt K, Gluhacevic von Krüchten L, Prante O, Keller M, Maschauer S. Neurotensin analogs by fluoroglycosylation at Nω-carbamoylated arginines for PET imaging of NTS1-positive tumors. Sci Rep. 2022; 12(1): 15028.

3. Bhandari A, Manthati SK, Mehrotra MM. Methods for synthesizing α4β7 peptide antagonists. 2017; Patent Number: WO2017165676.