# A Vibrational Analysis of Pyridoxal 5′-Phosphate Derivatives: Pyridoxal 5′-Phosphate-isopropylamine and Pyridoxal 5′-Phosphate‑(S)‑1-phenylethylamine

## TL;DR

This paper explores how vibrational spectroscopy can study PLP-dependent reactions by analyzing two external aldimines.

## Contribution

The study introduces a new method using vibrational spectroscopy to probe PLP's role in transamination reactions.

## Key findings

- Vibrational spectroscopy successfully identified functional group contributions in PLP-aldimines.
- DFT calculations and neutron scattering validated vibrational characteristics of noncrystalline PLP-aldimines.
- The findings establish a platform for monitoring PLP-dependent transamination processes using Raman spectroscopy.

## Abstract

The external aldimine, a pivotal Schiff base intermediate
in pyridoxal
5′-phosphate (PLP)-dependent enzyme-catalyzed reactions, plays
a central mechanistic role in the ω-transamination pathway used
for the synthesis of chiral amines in pharmaceutical production. To
investigate the potential of vibrational spectroscopy to probe molecular
interactions relevant to PLP’s role as a cofactor in transamination
reactions, two external aldimines, pyridoxal 5′-phosphate-isopropylamine
(PLP-IPAm) and pyridoxal 5′-phosphate-(S)-1-phenylethylamine
(PLP-PEA), are synthesized and analyzed by vibrational spectroscopy.
Single-molecule DFT calculations are employed to predict the vibrational
characteristics of both compounds. Inelastic neutron scattering measurements
validate the single-molecule DFT calculations for the noncrystalline
PLP-aldimines. The computational data sets guide the assignment of
ATR-IR and FT-Raman spectra of both external aldimines over the 400–4000
cm–1 range, enabling the identification of vibrational
bands from functional groups that may contribute to the transamination
mechanism. The characterization of discrete vibrational modes for
each external aldimine defines a platform by which vibrational spectroscopy
(e.g., Raman spectroscopy) could potentially be used to monitor PLP-dependent
transamination processes.