Cis aconitic anhydride

α-Methoxy-ω-amino poly(ethylene glycol) (MeO-PEG-NH₂) (M_w = 12,000 g mol⁻¹) was purchased from NOF CORPORATION (Tokyo, Japan). ξ-Trifluoroacetyl-l-lysine N-carboxyanhydride (Lys-(TFA)-NCA) was purchased from Chuo Kaseihin Co. Inc. (Tokyo, Japan). N,N-dimethylformamide (DMF) (purity > 99.5%) and methanol (purity > 99.5%) were purchased from Fujifilm Wako Pure Chemical, Co., Inc., (Tokyo, Japan). Diethyl ether (purity > 95%), cis-aconitic anhydride (CAA; purity > 95%), dextran sulfate (M_r ~40,000), and 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (1.0 M), Dulbecco’s phosphate-buffered saline (D-PBS), fetal bovine serum (FBS), penicillin-streptomycin and RPMI-1640 medium were purchased from Sigma-Aldrich (St. Louis, MO, USA). Oxalyl Chloride (purity > 98%) and anhydrous dichloromethane (purity > 98%) were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). The CT26 cells were obtained from Riken BioResource Center (Tsukuba, Japan).