Table 1 Screening of 2-EBA 2a–t and compounds 4a–c for modification of YTSSSKNVVR 1aa.

From: N-Terminal selective modification of peptides and proteins using 2-ethynylbenzaldehydes

Entry

Reagent

Conversion (%)b

N-terminal selectivity of mono-modified peptided

Efficiency of N-terminal modificatione

Mono-modifiedc

Di-modified

Total

N-terminus

Lysine

1

2a

61

3

8

72

96:4

0.85

2

2b

64

2

6

71

98:2

0.90

3

2c

60

3

5

68

96:4

0.88

4

2d

73

-

13

86

>99:1

0.85

5

2e

58

2

7

67

96:4

0.87

6

2f

27

1

-

28

97:3

0.96

7

2g

39

1

1

41

98:2

0.95

8

2h

64

-

4

68

>99:1

0.94

9

2i

69

2

7

78

98:2

0.88

10

2j

46

1

2

49

97:3

0.94

11

2k

53

2

3

58

97:3

0.91

12

2l

64

3

5

72

95:5

0.89

13

2m

58

4

3

65

93:7

0.89

14

2n

52

2

3

57

96:4

0.91

15

2o

56

3

5

64

95:5

0.88

16

2p

4.7

0.4

–

5

93:7

0.94

17

2q

26

–

74

100

>99:1

0.26

18

2r

65

5

25

95

93:7

0.68

19

2s

–

–

–

–

–

–

20

4a

–

–

–

–

–

–

21

4b

–

–

–

–

–

–

22f

4c

55

20

25

100

73:28

0.55

23

2t

70

1

9

80

98:2

0.88

  1. aConditions: YTSSSKNVVR 1a (0.1 mM) and reagent (2 mM) in 50 mM PBS (pH 6.5)/DMSO (9:1) solution (100 μL), 37 °C, 16 h.
  2. bDetermined by total ion count (TIC) of LC–MS analysis.
  3. cConversion of N-terminal modified peptide (or lysine-modified peptide) is determined by the conversion of mono-modified peptide and N-terminal selectivity of mono-modified peptide.
  4. dN-terminal selectivity is obtained by ratio of mono-modified peptide at N-terminal α-amino group to lysine ε-amino group as determined by extracted ion chromatogram (EIC) of LC-MS analysis.
  5. eEfficiency of N-terminal modification is equal to the conversion of N-terminal modified peptide over the total conversion.
  6. fModification was conducted at room temperature for 15 min.
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