AbstractIn 1980 the C‐terminal pentapeptide LGLAR (C3a 73–77) was described (Caporale, L. H. et al. J. Biol. Chem. 1980. 255: 10758) as the minimal sequence inducing a C3a‐specific activity. We have synthesized C3a‐analogue peptides connected to non‐peptidic acyl residues known to potentiate biological activity. Starting from the acylated hexapeptide fluorenylmethoxycarbonyl(Fmoc)‐aminohexanoyl(Ahx)‐ALGLAR, a related series of shorter peptides was synthesized. C3a‐specific activity was measured as ATP release from guinea pig platelets. Even the tripeptide LAR, acylated with Fmoc‐Ahx, exhibited C3a‐specific activity. With 0.34% C3a activity, it was even more potent than the native LGLAR sequence which has 0.01% activity. N‐terminal extension of the acylated tripeptide LAR by adding one to three alanines increased activity tenfold up to 3.26% (Fmoc‐Ahx‐AAALAR), while N‐terminal addition of three glycine residues (Fmoc‐Ahx‐GGGLAR) only increased activity to 0.83% of native C3a. Furthermore, a stimulus‐specific desensitization could be observed. Fmoc‐Ahx‐R and Fmoc‐Ahx‐AR exhibited neither activity nor desensitizing capacity, but the addition of four alanines to the dipeptide AR led to a sequence (Fmoc‐Ahx‐AAAAAR) with a C3a‐specific activity of 0.14%. Even arginine prolonged N‐terminally with five glycines (Fmoc‐Ahx‐GGGGGR) exhibited some C3a‐specific activity so that for biological activity only the appropriate presentation of arginine seems to be essential.