Fluorescence properties of the anti-tumour alkaloid luotonin A and new synthetic analogues: pH modulation as an approach to their fluorimetric quantitation in biological samples

► This is the first study on the fluorescence properties of luotonin A analogues. ► Fluorescence and NMR experiments showed complex prototropic equilibria for luotonin A derivatives. ► A good correlation between their acid-base behaviour and their structures has been found. ► Although they behave as very weak bases, they are able to bind protons at their two basic nitrogens. ► We took advantage of their fluorescence to develop an analytical method enabling their quantitation.