Fig. 4

Synthetic scheme of a near-infrared-emitting pH probe conjugatable to proteins. Reagents: a Ag₂SO₄/1,4-dioxane, H₂O, reflux, y. 51%; b t-BuOH, H₂SO₄, Mg₂SO₄/CH₂Cl₂, r.t., y. 51%; c (i) s-BuLi/THF, – 78 °C, (ii) IGe-xanthone/THF, – 78 °C to r.t., (iii) 2 N HCl, r.t., (iv) TFA, r.t., y. 52%; d NHS, WSCD/DMF, r.t., y. 48%