Was IPTG intentionally first synthesized as an analogue of lactose through substrate engineering? Or, was it previously synthesized and was stumbled upon as being an inducer of the lac operon?
IPTG is an analog of allolactose (a lactose metabolite) that is able to induce the transcription of the Lac operon and is not degraded inside the cell by its Sulfur atom.
IPTG was first characterised as lactose-like metabolite and then was determined that it could act over the Lac operon as an inducer as lactose without its degradation.