Philip G. Williams, University of Hawai‘i at Ma̅noa, Honolulu, USA, and colleagues have isolated leptazolines—natural products with an oxazoline core (example pictured)—from cyanobacteria and used NMR spectroscopy to assign the compounds’ structures. To make the assignments, the measured NMR shifts were compared to shifts of the proposed structures, which were calculated using density functional theory (DFT).
When the team tried to replicate the calculated NMR shifts, they made a surprising discovery: The resulting shifts were different on computers with different operating systems, even though the same procedure was used. The researchers found the cause in software that is often used to calculate NMR shifts: the so-called “Willoughby–Hoye” scripts .
These scripts use results from two different types of output files of DFT calculations to find the NMR shifts. As it turns out, they depend on the operating system to sort these two types of files in the same manner so that the correct files are paired. However, this is not a given. Linux, for example, can sort files in a directory completely differently than Windows—depending on the configuration of the system. The team tested the scripts on Ubuntu 16 (a Linux operating system), Windows 10, and two different versions of macOS. They found incorrect results for Ubuntu and one of the macOS versions.
The researchers have amended the scripts so that they sort the files correctly and alert the user to potential problems. They point out that a significant number of published research articles could be affected and the operating system used is seldom stated. Thus, the team calls for other researchers to check their results.
- Characterization of Leptazolines A–D, Polar Oxazolines from the Cyanobacterium Leptolyngbya sp., Reveals a Glitch with the “Willoughby–Hoye” Scripts for Calculating NMR Chemical Shifts,
Jayanti Bhandari Neupane, Ram P. Neupane, Yuheng Luo, Wesley Y. Yoshida, Rui Sun, Philip G. Williams,
Org. Lett. 2019.
-  A guide to small-molecule structure assignment through computation of (1H and 13C) NMR chemical shifts,
Patrick H. Willoughby, Matthew J. Jansma, Thomas R. Hoye,
Nat. Protoc. 2014, 9, 643–660.