A method for preparing a biomaterial to which a compound represented by formula 2 is coupled, comprising a step of reacting a compound represented by formula 1 and a biomaterial containing tyrosine present on the surface in an aqueous solution in the presence of a compound represented by formula 3: (In formula 1, A is nonsubstituted or substituted C 6-14 arylene or 5-20 membered nonsubstituted or substituted heteroarylene containing one or more hetero atoms selected from the group consisting of N, O and S, wherein the substituted arylene and heteroarylene can be substituted with one or more selected from the group consisting of halogen, straight or branched C 1-5 alkyl, straight or branched C 1-5 alkoxy, =O and -OH; L is any one selected from the group consisting of S, O, NR 3, -NHC (=O) -, -C (=O) NH- and straight or branched C 1-10 alkylene, or a combination thereof, and R 3 is hydrogen or straight or branched C 1-3 alkyl; and B is a compound for imparting functionality to a biomaterial, wherein B is any one selected from the group consisting of alkoxy or hydroxypolyalkyleneoxide having a weight average molecular weight of 100 to 50000, poly(2-alkyl methacryloyloxyethyl phosphorylcholine) having a weight average molecular weight of 100 to 50000, poly(alkyl methacylate) having a weight average molecular weight of 100 to 50000, and peptide polymers having a weight average molecular weight of 100 to 50000, wherein alkoxy is straight or branched C 1-10 alkoxy, alkylene is straight or branched C 1-10 alkylene, and alkyl is straight or branched C 1-10 alkyl); (In formula 2, A, L and B are as defined in formula 1.); (In formula 3, X is N; and R a, R b, R c, R d and R e are independently hydrogen or straight or branched C 1-5 alkyl, R a and R e can form 5-8 membered heterocycloalkenyl along with N to which they are attached, and R b and R c can form 5-8 membered heterocycloalkyl along with N and X to which they are attached). A is nonsubstituted or substituted C 6-14 arylene or 5-20 membered nonsubstituted or substituted heteroarylene containing one or more hetero atoms selected from the group consisting of N, O and S, wherein the substituted arylene and heteroarylene can be substituted with one or more selected from the group consisting of halogen, straight or branched C 1-5 alkyl, straight or branched C 1-5 alkoxy, =O and -OH; L is any one selected from the group consisting of S, O, NR 3, -NHC (=O) -, -C (=O) NH- and straight or branched C 1-10 alkylene, or a combination thereof, and R 3 is hydrogen or straight or branched C 1-3 alkyl; and B is a compound for imparting functionality to a biomaterial, wherein B is any one selected from the group consisting of alkoxy or hydroxypolyalkyleneoxide having a weight average molecular weight of 100 to 50000, poly(2-alkyl methacryloyloxyethyl phosphorylcholine) having a weight average molecular weight of 100 to 50000, poly(alkyl methacylate) having a weight average molecular weight of 100 to 50000, and peptide polymers having a weight average molecular weight of 100 to 50000, wherein alkoxy is straight or branched C 1-10 alkoxy, alkylene is straight or branched C 1-10 alkylene, and alkyl is straight or branched C 1-10 alkyl); (In formula 2, A, L and B are as defined in formula 1.); (In formula 3, X is N; and R a, R b, R c, R d and R e are independently hydrogen or straight or branched C 1-5 alkyl, R a and R e can form 5-8 membered heterocycloalkenyl along with N to which they are attached, and R b and R c can form 5-8 membered heterocycloalkyl along with N and X to which they are attached). A, L and B are as defined in formula 1.); (In formula 3, X is N; and R a, R b, R c, R d and R e are independently hydrogen or straight or branched C 1-5 alkyl, R a and R e can form 5-8 membered heterocycloalkenyl along with N to which they are attached, and R b and R c can form 5-8 membered heterocycloalkyl along with N and X to which they are attached). X is N; and R a, R b, R c, R d and R e are independently hydrogen or straight or branched C 1-5 alkyl, R a and R e can form 5-8 membered heterocycloalkenyl along with N to which they are attached, and R b and R c can form 5-8 membered heterocycloalkyl along with N and X to which they are attached).