Vol.:(0123456789) 1 3 International Journal of Peptide Research and Therapeutics https://doi.org/10.1007/s10989-020-10061-3 Synthesis, Antioxidant Activity, and Structure–Activity Relationship of SCAP1 Analogues Rani Maharani 1,2  · Ace Tatang Hidayat 1,2  · Irana Rahmawati Sabana 1  · Anastasya Firdausi 1  · Alifah Aqmarina 1  · Dessy Yulyani Kurnia 1  · Mufti Hanif Amrullah 1  · Achmad Zainuddin 1  · Desi Harneti 1  · Nurlelasari 1  · Unang Supratman 1,2 Accepted: 7 April 2020 © Springer Nature B.V. 2020 Abstract Nine analogues of antioxidant peptide SCAP1 were successfully synthesised using a solid-phase method on a 2-chlorotrytil resin. The compounds were obtained in a range of yields of 7.0–57.8%. The occurrence of aggregation during the synthesis is suspected to be responsible for the poor yields. All peptides were characterized by high-resolution time-of-fight mass spectrometry (HR-TOFMS) and nuclear magnetic resonance (NMR). The antioxidant activities of the SCAP1 analogues as well as SCAP1 were analysed utilising the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assay. The results revealed that all of the analysed peptides exhibited moderate antioxidant properties. Moreover, the evaluation of the structure–activity relationship showed that the Asn residue is an important requirement for the antioxidant activity of SCAP1. The replacement of Asn with other amino acid residues (Thr, Pro, Tyr, Trp and Phe) resulted in a decrease in the IC 50 values of the peptides. Notably, however, the replacement of the Lys residue with Val marginally increased the activity. Keywords SCAP1 · Antioxidant peptide · Solid-phase peptide synthesis · DPPH assay Introduction Antioxidant peptides have been found in numerous plant or animal protein hydrolysates (Nikoo et al. 2014; Daliri et al. 2017; Ye et al. 2018). SCAP1 is a hydrolysate obtained from the enzymatic hydrolysis of oyster protein (Saccos- trea cucullata). It has been demonstrated to exhibit anti- oxidant activity, with a percentage of the 2,2-diphenyl- 1-picryl-hydrazyl-hydrate (DPPH) radical scavenging of 83.79 ± 0.53% (Umayaparvathi et al. 2014). Structurally, the peptide consists of a sequence of leucine-alanine-aspar- agine-alanine-lysine amino acids, in which all of the residues are L-confgured. Notably, the successful synthesis of SCAP1 using a solid- phase method has been previously described by Sabana et al. (2019). However, the antioxidant activity of the synthetic SCAP1 product has not been evaluated. Thus, in order to establish the structure–activity relationship of the peptide, in the present study, several analogues of SCAP1 were designed and synthesised. The synthesis of the analogues involved a similar method to the one originally described for SCAP1. Furthermore, the antioxidant activity of SCAP1 and its analogues was assessed utilising the DPPH method. Experimental Reagent and Apparatus All reagents and solvents were used as supplied, with- out any further purification. Fmoc- L-amino acids, [bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5- b]pyridinium 3-oxide hexafluorophosphate (HATU), 1-hydroxy-7-azabenzotriazole (HOAt) and 2-chlorotrityl chloride resin were purchased from GL Biochem (Shanghai, China). Dichloromethane (DCM), N,N-dimethylformamide * Rani Maharani r.maharani@unpad.ac.id 1 Department of Chemistry, Universitas Padjadjaran, Jl. Raya Bandung-Sumedang Km 21 Jatinangor, 45363 Sumedang, West Java, Indonesia 2 Central Laboratory, Universitas Padjadjaran, Jl. Raya Bandung-Sumedang Km 21 Jatinangor, 45363 Sumedang, West Java, Indonesia