General procedure for the synthesis of 2,2',2'',2''-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra)tetraacetamide from 2-bromoacetamide and rotenone: In a 100 mL round-bottomed flask fitted with a reflux condenser and stirring bar, 1.4696 g of rotenone (8.5 mmol) was added. A mixture of 5.44 g 2-bromoacetamide (39.4 mmol, 4.6 eq.) and 4.5748 g triethylamine (44.9 mmol, 5.3 eq.) dissolved in 30 mL of anhydrous ethanol was subsequently added. The reaction mixture was refluxed at 80 °C for 4 h. A white precipitate gradually formed in the flask during the reaction. Upon completion of the reaction, the reaction was cooled to room temperature, the precipitate was decanted and transferred to a 250 mL round bottom flask. The precipitate was dissolved in 200 mL of hot 80% ethanol/20% water solvent mixture. The volume of the solution was concentrated to approximately 30% of the original volume using a rotary evaporator and the concentrate was subsequently placed in a refrigerator overnight to precipitate white crystals. The crystals were separated by filtration, transferred to a 50 mL round bottom flask and dried under vacuum on a Schlenk line for several hours to give the target product in 66% yield. The product was characterized by ESI-MS and NMR (1H NMR and 13C NMR): ESI-MS: m/z = 401.3 (100%), 402.3 (15%) [M + H]+; 423.4 (25%), 424.4 (<10%) [M + Na]+. 1H NMR (500 MHz, D2O), δ (ppm): 3.02 (s, amide side chain CH2, 8H), 2.57 (s, rotary tannin ring CH2, 16H).13C NMR (125 MHz, D2O), δ (ppm): 174.07 (carbonyl carbon), 55.86 (amide CH2), 50.42 (cyclic CH2).
