Mostly pure 4-(azidomethyl)benzoic acid NHS ester

I'm at a small biotech startup and we've been making azido-NHS esters ourselves since chemical suppliers charge such a huge markup for them. This particular compound is interesting because I could find very few direct references in the literature.

This paper uses it, and claims it was made following a previous literature procedure:

The cited paper has no mention of the synthesis of said compound. They claim it was made following a previous procedure:

The final paper also has no mention of the synthesis in the paper or the SI, only the parent (4-azidomethyl)benzoic acid in the SI. The authors seem to have materialized the compound into existence out of thin air! 😂