Concluding with a third robust synthetic application of this strategy, the methodology demonstrates significant utility in the late-stage functionalization (LSF) of peptides on solid-phase, enabling the modification of complex peptides under mild conditions and obviating the need for tedious de-novo synthesis (Figure ). We initially commenced to develop a direct decarboxylative C1 homologation, beginning with N-Boc (L)-Proline, but we were met with failure to produce the desired product 3 (see Supporting Information, section 5.1). This result was linked to the noted sensitivity of aldehyde sulfonyl hydrazones to bases, which are indispensable to promote the decarboxylation process. Consequently, our investigation focused on the use of well-established N-(acyloxy)phthalimides (NHPI-based esters) as redox-active esters (RAEs) in an effort to sidestep the necessity for bases during the decarboxylative generation of nucleophilic carbon radicals. An exhaustive screening of all reaction parameters (see Supplementary Information, section 5.2) led us to discover that the targeted homologated product 3 could be obtained in excellent yields (Table , Entry 1, 90% yield) when a dichloromethane (0.1 M) solution composed of ethyl glyoxalate-derived 4-trifluoromethyl-phenyl sulfonyl hydrazone 2a (1.0 equiv.) as the radical acceptor, N-Boc (L)-Proline RAE 1a (1.0 equiv.) as the radical precursor, Hantzsch ester (HE, 1.5 equiv.) as the reductive quencher, and disodium Eosin Y (EYNa2, 10 mol%) as the photocatalyst was irradiated with blue LEDs (40W Kessil, 456 nm, PR160L) for 12 hours. The yield reflects the one obtained for the final product 3, achieved when the hydrazinyl intermediate was swiftly subjected to cleavage conditions in ethanol, according to our previous report. Evaluating a two-step one-pot procedure, with trifluorotoluene as the solvent, revealed diminished yields of 3, underscoring the pivotal role dichloromethane plays in the photocatalytic cycle (Table , Entry 2). Surprisingly, an excess of radical acceptor 2a did not markedly influence the reactivity (Table , Entry 3). Noteworthy is the underperformance of more expensive organophotoredox catalysts like 4CzIPN, 3DPA2FBN or the widely-used transition-metal based photocatalyst Ru(bpy)3PF6 (Table , Entries 4-6). HE played a major role in the transformation, as other reductive quenchers, such as DABCO, DIPEA, or tetramethylguanidine entirely inhibited the reaction (see Supplementary Information, Table ).