Beside head-to-side-chain macrocyclization, head-to-tail cyclization starting from EBX on the N-terminus was also possible (products 13k-t). Ser (13l), Met (13n), Asp (13p), Gln (13q), His (13r) were well-tolerated under the reaction conditions. The commercially available peptide FLEEV, a synthetic substrate of the enzyme -glutamyl carboxylase (GGCX), can be also cyclized in an efficient way to give 13o. Free Tyr and Trp, which can be easily oxidized under photoredox condition, are not compatible with the cyclization. Peptide sequences, containing free Lys and Arg, were also tested under our conditions. The corresponding cyclic peptides (13s, 13t) were formed in lower yield accompanied with more by-products. Up to now, we had demonstrated the potential of our method for the synthesis of new macrocycles by diversifying both the incorporated amino acids and the ring size. As a next step, we wondered if the method could also be applied to the synthesis of synthetic analogues of known macrocyclic natural products. As a first target, we selected Sanguinamide A ( ), a natural product extracted from Hexabranchus sanguineus that has been shown to have high membrane permeability and oral absorption. We targeted the thioazole moiety to be replaced by the phenylacetylenyl motif, as this led to an easy-to-synthesize natural amino acid sequence. The macrocyclization step gave 13p in 41% yield and 13:1 diastereoselectivity. An advantage of the alkyne group is that the shape of the macrocycle can be easily changed by reducing the triple bond to either alkene 15 or alkane 16, leading to completely different conformations. As a second target, we selected Asperflosamide (17), recently isolated from a marine sponge-derived fungus. In this case, replaced the potentially labile ester group in the macrocycle by the rigid and stable phenylalkyne linker. The desired macrocycle 13q could be obtained in 28% isolated yield and 4.5: 1 dr. The reactions were performed using peptide-EBX (0.01 mmol, 1 equiv.), 30 mol% 4CzIPN and 10 equiv. of K2HPO4 (2 M in milliQ water) in DMA (10 mM) at room temperature under blue LEDs for 30 min. Yields of isolated products are given. a dr was determined based on 1 H-NMR of isolated product. b dr was not determined. The dr was determined from the HPLC-UV ratio (210 nm) of the reaction crude mixture. d (30 mol%) 4Cl-CzIPN was used as photocatalyst. e Diastereoisomers separable by RP-HPLC. f The yield was reported based the HPLC-UV ratio of cyclic peptides and byproducts.