# Computational NMR Study of Cryptolepis Alkaloids: Could the Structural Misassignment of Cryptospirolepine Have Been Avoided?

## TL;DR

This paper shows how computational methods can detect and correct structural errors in complex molecules like cryptospirolepine using NMR data.

## Contribution

The study demonstrates that computational NMR methods can effectively identify and correct structural misassignments in complex alkaloids.

## Key findings

- Computational methods achieved high correlation with experimental NMR chemical shifts for thirteen Cryptolepis alkaloids.
- The corrected mean absolute error for proton and carbon shifts was 0.13 ppm and 1.5 ppm, respectively.
- The study suggests spectral reassignments and predicts missing chemical shifts for some compounds.

## Abstract

It is demonstrated that by using modern computational methods, it is possible to identify potential structural misassignments for even molecules as complex as cryptospirolepine. While methods that rely on anisotropic nuclear magnetic resonance (NMR) methods can also be used to offer a powerful orthogonal means of structure elucidation and verification, the present computational study should be feasible in most chemistry departments with access to sophisticated computational facilities. From the overall correlations calculated against experimental 1H and 13C NMR chemical shifts in the series of thirteen Cryptolepis alkaloids, it follows that, generally, they provide a very high level of correlation. The corrected mean absolute error (CMAE) is found to be at the level of 0.13 and 1.5 ppm for, proton and carbon chemical shifts, respectively, which is only about 2 and 1% of their ranges. Based on the performed calculations, some spectral reassignments are suggested, and a number of missing (unknown) experimental chemical shifts are predicted.