# Bioorganometallic tagging of N-acetylhistamine with an Fe(CO)3 unit: synthesis, X-ray structure, and protonation behavior

## TL;DR

This paper describes a new way to label a histamine derivative with an iron carbonyl complex for potential use in bioorganometallic chemistry and imaging.

## Contribution

The study introduces a novel organometallic labeling strategy for biomolecules using an Fe(CO)3 unit with confirmed stereochemistry and stability.

## Key findings

- The Fe(CO)3 unit was successfully coupled with N-acetylhistamine in a regio- and stereoselective manner.
- X-ray analysis confirmed a rigid and well-defined structure with exo stereochemistry.
- The complex remains stable in aqueous solutions between pH 5 and 8 with increased basicity compared to the free ligand.

## Abstract

This study highlights the potential of organometallic carbonyl complexes as selective markers for biomolecules, enabling sensitive infrared (IR) detection. The regio- and stereoselective coupling of N-acetylhistamine, a histidine analogue, with the precursor complex 1 [Fe(CO)3(1,4-η5-N-pyridiniocyclohexa-1,3-diene)] BF4 affords the labeled complex 3 [Fe(CO)3(1,4-η5-N-acetylhistaminocyclohexa-1,3-diene)]. X-ray diffraction (XRD) confirms the exo stereochemistry and reveals a rigid, well-defined architecture. IR and 1H nuclear magnetic resonance spectroscopic studies combined with IR-monitored acid–base titration demonstrate the complex’s stability in aqueous media between pH 5 and 8, alongside a modest increase in basicity relative to the free ligand. These findings establish the Fe(CO)3 moiety as a robust platform for selective labeling of peptides and proteins, paving the way for targeted applications in bioorganometallic chemistry and spectroscopic imaging.