Table 1 Optimization of the VTT-promoted thioacid esterification conditionsa

From: Rapid vinyl thianthrenium tetrafluoroborate-promoted thioacid-based native chemical ligation and its applications in chemical protein synthesis

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Entry

VTT [eq.]

Solvent

pH

Temp. [oC]

Time

[h]

Yield

[%]b

1

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

2.0

25

4 (2)

>90 (88)

2

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

3.0

25

4 (2)

>90 (89)

3

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

4.0

25

4 (2)

>90 (89)

4

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

5.0

25

4 (2)

90 (87)

5

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

6.0

25

4 (2)

39 (52)c

6

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

7.0

25

4 (2)

9 (20)c

7

1.1

6.0 M Gn·HCl, 0.2 M Na2HPO4

5.0

25

4 (2)

88 (85)

8

1.3

6.0 M Gn·HCl, 0.2 M Na2HPO4

5.0

25

4 (2)

>90 (89)

9

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4

5.0

37

4 (2)

64 (75)d

10

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 10% DMF

5.0

25

2

92

11

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 20% DMF

5.0

25

2

>95

12

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 30% DMF

5.0

25

2

90

13

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 50% DMF

5.0

25

2

86

14

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 10% ACN

5.0

25

2

88

15

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 20% ACN

5.0

25

2

87

16

1.2

6.0 M Gn·HCl, 0.2 M Na2HPO4, 30% ACN

5.0

25

2

87

  1. aAll reactions were conducted on a 2.0 mM scale.
  2. bYield was determined by integrated areas of RP-HPLC peaks at λ = 214 nm.
  3. cByproduct (MW = 452, rt = 18.4 min) resulted in low yield.
  4. dByproduct (MW = 452, rt = 18.4 min) and byproduct (rt = 26.4 min) resulted in low yield; For more details, refer to the supplementary information.
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