Miscellaneous Compounds

The chiral NMR solvating agent 1-(9-anthryl)-2,2,2-trifluoroethanol (TFAE) has been separated by a variety of chromatographic techniques and has became a reference compound for testing new optically active selectors. For example, a values of 2.02 and 2.34

Table 5 Enantioseparation of racemic Dns-amino acids with chiral mobile phases

Dns-Amino acid

hRF1

hRF2

ab

Eluent

Remarks

Abu

42(L)

47

1.22

C

Reversed-phase plates: 5 cm x 20 cm and 20 cm x 20 cm,

Ala

40(L)

47

1.33

G

KC18F, Whatman, USA. Development time 6-8 h.

Arg

55(L)

65

1.52

H

Eluents: acetonitrile-0.133mol L~1 £-CD, 25 : 75 (A);

Asn

60(L)

69

1.48

H

methanol-0.163mol L~1 ^-CD, 35 : 65 (B);

Asp

64(L)

70

1.31

A

acetonitrile-0.151 mol L~1 ^-CD, 30 : 70 (C);

Cit

54(L)

63

1.45

H

acetonitrile-0.133mol L~1 £-CD, 20 : 80 (D);

Cys

37(L)

42

1.23

I

methanol-0.151 mol L~1 ^-CD, 30 : 70 (E);

Gln

57(L)

66

1.46

H

acetonitrile-0.231 mol L~1 ^-CD, 35 : 65 (F);

Glu

65(L)

72

1.38

B

methanol-0.2 mol L~1 ^-CD, 35 : 65 (G);

His

58(L)

64

1.28

H

acetonitrile-0.2 mol L~1 ^-CD, 20 : 80 (H);

Ile

33(L)

40

1.35

L

methanol-0.2 mol L~1 ^-CD, 55 : 45 (I);

allo-Ile

30(L)

38

1.43

L

acetonitrile-0.2 mol L~1 ^-CD, 32 : 68 (L);

Leu

30(L)

35

1.25

C

methanol-saturated ^-CD, 60 : 40 (M);

Lys

35(L)

39

1.18

M

methanol-0.2 mol L~1 ^-CD, 50 : 50 (N).

Met

34(L)

38

1.19

C

Aqueous solutions of ^-CD also contain urea (saturated

Nle

24(L)

28

1.23

C

solution) and 3.5% sodium chloride.

Nva

32(L)

34

1.09

C

Visualization: UV254.

Orn

35(L)

40

1.23

M

Phe

35(L)

39

1.18

C

Pro

39(L)

41

1.08

N

Ser

41(L)

47

1.27

D

Thr

42(L)

51

1.43

E

Trp

43(L)

45

1.08

F

Tyr

23(L)

26

1.17

M

Val

36(L)

43

1.34

C

N-Methyl-Val

24(L)

28

1.23

N

Abu

34(L)

56

2.47

O

RP-18W/UV254 plates (Art. 811075, Macherey-Nagel).

Asp

68(D)

79

1.77

O

Migration distance 7 cm.

Glu

45(D)

65

2.27

O

Eluents: 5% BSA in 0.1 mol L~1 acetate buffer (O);

Leu

6(D)

15

2.76

P

5% BSA and 1 % NaCl in 0.5 mol L~1 acetic acid (P);

Met

32(L)

50

2.12

Q

6% BSA in 0.1 mol L~1 acetate buffer (Q);

Nle

38

50

1.63

Q

7% BSA in 0.5 mol L~1 acetic acid (R).

Nva

25(L)

73

8.13

O

Eluents also contain 2% isopropanol.

Phe

24(L)

45

2.59

Q

Visualization: UV254.

Ser

39(D)

46

1.33

R

Thr

34(L)

43

1.46

Q

25(D)

32

1.41

R

Trp

37(D)

62

2.77

O

Val

20(L)

33

1.97

O

were obtained, respectively, on OPTI-TAC F254 (Antec) plates eluted with ethanol-water 80 : 20 (v/v) and on SIL C18-50/UV254 layers using 6% BSA in 0.05 mol L_1 sodium tetraborate containing 20% isopropanol (pH 9.75) as mobile phase.

( ± )-1-(9-Fluorenyl)ethanol an analogue of TFAE, was also resolved on home-made MCTA plates elut-ing with 2-propanol-water 80 : 20 (v/v) (a = 2.24).

The separation of chiral compounds with restricted rotation, as in the case of binaphthyl type of substances, can be effected both on CSPs and with CMPs. The first technique requires the use of MCTA plates to resolve ( + )-1,1'-binaphthyl-2,2'-diamine (a = 1.99) while the latter involves chiral mobile phases containing BSA for the separation of ( +)-1,1'-bi-2-naphthol (a = 2.15) and ( + )-binaphthyl-2,2'-diyl-hydrogen phosphate (a = 4.65).

The enantiomeric separations of synthetic pyreth-roids, such as alfamethrin and fenpropathrin, on home-made MCTA plates with ethanol-water 80 : 20 (a = 1.37 and 1.20, respectively) should be noted since their optical antipodes have different rates of degradation and biological activity towards animals and plants.

The resolution of racemic fenoxaprop-ethyl on the above-mentioned CSP (a = 1.52, isopropanol-water 80 : 20) in interesting since chlorophenoxyalkyl car-boxylic acids and esters are widely used herbicides.

Table 6 Enantioseparation of derivatized amino acids by chiral TLC

Derivative

hRF,a

hRF2

rjb

Rsc

Plate

Eluent'

Fmoc-Ala

89(L)

37

1.43

1.1

SIL C18-50/UV254

A

Fmoc-Chad

17(L)

30

2.09

2.3

SIL C18-50/UV254

B

Fmoc-Leu

29(L)

36

1.37

1.3

SIL C18-50/UV254

C

Fmoc-Met

20(D)

28

1.55

1.1

SIL C18-50/UV254

D

Fmoc-Nle

18(L)

27

1.68

1.4

SIL C18-50/UV254

B

Fmoc-Nva

19(L)

27

1.57

1.6

SIL C18-50/UV254

B

Fmoc-Phe

41(L)

50

1.43

1.2

SIL C18-50/UV254

C

Fmoc-Pro

47(D)

77

3.78

1.6

SIL C18-50/UV254

B

34(D)

40

1.29

2.0

MCTA

E

Fmoc-Trp

20(D)

41

2.79

2.7

SIL C18-50/UV254

D

Fmoc-Val

36(L)

43

1.35

2.3

SIL C18-50/UV254

C

DNP-Abu

59

89

5.75

4.0

RP-18W/UV254

F

DNP-Cit

34

41

1.35

1.7

RP-18W/UV254

G

DNP-Eth

45

61

1.94

2.0

RP-18W/UV254

G

DNP-Eth(O2)

26

35

1.53

2.0

RP-18W/UV254

H

DNP-Leu

28(L)

54

3.02

3.6

RP-18W/UV254

I

24(D)

31

1.42

1.8

SIL C18-50/UV254

L

DNP-Met

28

61

4.02

3.3

RP-18W/UV254

M

DNP-Met(O2)

44(D)

50

1.27

2.0

RP-18W/UV254

N

DNP-Met(O)

27

34

1.39

2.3

RP-18W/UV254

N

DNP-Nle

31

63

3.78

5.1

RP-18W/UV254

I

DNP-Nva

40

89

12.19

5.0

RP-18W/UV254

O

DNP-Pip

45

56

1.56

1.3

RP-18W/UV254

F

DNPy-Ala

47

53

1.27

1.6

RP-18W/UV254

H

DNPy-Leu

45

70

2.85

4.0

RP-18W/UV254

N

38

43

1.23

1.5

SIL C18-50/UV254

L

23

31

1.50

2.5

SIL C18-50/UV254

P

DNPy-Met

31

56

2.61

4.2

RP-18W/UV254

Q

DNPy-Nle

25

63

5.11

5.7

RP-18W/UV254

N

DNPy-Nva

21

31

1.69

2.3

RP-18W/UV254

H

DNPy-Phe

28

61

4.02

5.0

RP-18W/UV254

Q

47

51

1.17

1.2

SIL C18-50/UV254

L

18

26

1.60

2.0

SIL C18-50/UV254

P

DNPy-Trp

30

49

2.24

5.0

SIL C18-50/UV254

L

DNB-Leu

34(L)

51

2.02

3.0

RP-18W/UV254

N

DNB-PhenylGly

30(L)

67

4.75

7.3

RP-18W/F254S

N

MTH-Pro

12

16

1.39

1.3

RP-18W/UV254

R

33

37

1.19

1.0

MCTA

E

MTH-Phe

43

49

1.27

1.7

MCTA

S

MTH-Tyr

42

45

1.13

1.0

MCTA

E

PTH-Pro

13

25

2.23

2.5

MCTA

E

N-[1-(1-Naphthyl)ethyl]phthalamic acid

54(R)

58

1.17

1.6

MCTA

T

N-Benzylproline ethyl ester

19(D)

22

1.20

1.0

MCTA

U

Amethopterin

9(L)

19

2.34

2.3

RP-18W/UV254

V

N-Acetyl-5-methyl-Trp

33

76

6.44

3.0

RP-18W/UV254

M

N-CBZ-Trp

44(D)

88

9.33

3.0

RP-18W/UV254

Z

W-i-BOC-Trp

16(L)

23

1.57

1.2

RP-18W/UV254

V

«-i-BOC-p-nitro-Phe

20(D)

30

1.71

2.3

SIL C18-50/UV254

W

Ala-8-NA

68(L)

76

1.49

1.5

SIL C18-50/UV254

Y

59

66

1.35

-

KC18F

J

Leu-8-NA

54(L)

64

1.50

2.0

SIL C18-50/UV254

L

Met-8-NA

45(L)

55

1.50

2.3

SIL C18-50/UV254

L

Ala-p-NA

12(L)

14

1.19

0.4

RP-18W/UV254

K

Leu-p-NA

4(L)

7

1.81

1.2

RP-18W/UV254

K1

19(L)

23

1.27

1.0

SIL C18-50/UV254

K2

56(L)

63

1.33

1.7

SIL C18-50/UV254

cRs = 2x (distance between the centres of two adjacent spots)/(sum of the width of the two spots in the direction of development). tha = ^-Cyclohexylalanine.

"Eluents: A = 6% BSA, 23% 2-propanol, 0.1 mol L"1 acetate buffer; B = 5% BSA, 23% 2-propanol, 0.1 mol L"1 acetate buffer; C = 5% BSA, 36% 2-propanol, 0.1 mol L"1 acetate buffer; D = 6% BSA, 12% 2-propanol, 0.1 mol L"1 acetate buffer; E = 2-propanol/water 60 : 40 (v/v); F = 4% BSA, 2% 2-propanol, 0.1 mol L"1 acetate buffer (10°C); G = 6% BSA, 2% 2-propanol, 0.1 mol L"1 acetate buffer; H = 4% BSA, 1% NaCl, 2% 2-propanol, 0.5 mol L"1 acetic acid (10°C); I = 4% BSA, 2% 2-propanol, 0.05 mol L"1 phosphate buffer; L = 0.15 mol L"1 j8-CD in a water-acetonitrile solution (80 : 20, v/v) containing 26% urea and 3% NaCl; M = 3% BSA, 2% 2-propanol, 0.05 mol L"1 phosphate buffer; N = 5% BSA, 2% 2-propanol, 0.1 mol L"1 acetate buffer; O = 4% BSA, 2% 2-propanol, 0.1 mol L"1 acetate buffer; P = Hydroxypropyl-^-CD (13.8 g) in water-acetonitrile-aceticacid (45 : 4 : 1, v/v/v, 100 mL); Q = 2% BSA, 2% 2-propanol, 0.1 mol L"1 acetate buffer; R = 9% BSA, 2% 2-propanol, 0.1 mol L"1 acetate buffer; S = 2-propanol-water80 : 20 (v/v); T = ethanol-water70 : 30 (v/v); U = 2-propanol-water40 : 60 (v/v); V = 8% BSA, 2% 2-propanol, 0.5 mol L"1 acetic acid; Z = 5% BSA, 2% 2-propanol, 0.5 mol L"1 acetic acid; W = 6% BSA, 6% 2-propanol, 0.05 mol L"1 NaHCO3 + 0.05 mol L"1 Na2CO3; Y = 0.1 mol L"1,8-CD in a water-acetonitrile solution (80 : 20, v/v) containing 20% urea and 3% NaCl; J = 0.163 mol L"1 ,8-CD in a water-methanol solution (65 : 35, v/v) containing 3.5% NaCl and saturated with urea; K = 8% BSA, 3% 2-propanol, 0.1 mol L"1 acetate buffer; K1 = 6% BSA, 8% 2-propanol, 0.1 mol L"1 acetate buffer; K2 = 8% BSA, 20% 2-propanol, 0.1 mol L"1 acetate buffer.

Table 7 Separation of enantiomeric a-hydroxycarboxylic acids on HPTLC-CHIR platesa

Racemate hRF

hRF:

Eluent"

Mandelic acid 4-Bromo-mandelic acid 4-Chloro-mandelic acid

3-Hydroxy-mandelic acid

4-Hydroxy-mandelic acid 3,4-Dihydroxy-mandelic acid 4-Hydroxy-3-methoxy-

mandelic acid 2-Hydroxy-2-phenyl-

propanoic acid 2-Hydroxy-3-phenyl-propanoic acid Lactic acid 2-Hydroxy-butanoic acid 2-Hydroxy-3-methoxy-

butanoic acid 2-Hydroxy-4-methylthio-

butanoic acid 2-Hydroxy-pentanoic acid 2-Hydroxy-3-methyl-

pentanoic acid 2-Hydroxy-4-methyl-

pentanoic acid 2-Hydroxy-hexanoic acid 2-Hydroxy-octanoic acid 2-Hydroxy-tetradecanoic acid

2-Hydroxy-hexadecanoic acid 2-Hydroxy-docosahexanoic acid

36 33 35 47 45 33

36 34

48 44 42 59 57

44 33

50 49

1.44

1.62

1.99

1.99

^Migration distance, measured from concentrating zone, 13 cm; visualization: (a) the plates were dipped in MnCl2-sulfuric acid heating up to 120°C for 30 min for aromatic a-hydroxycarboxylic acids; (b) the plates were dipped for 2 s in vanadium (V)-sulfuric acid solution and dried at room temperature for c. 45 min for aromatic and aliphatic a-hydroxycarboxylic acids.

dEluents: A = dichloromethane/methanol 45:5 (v/v); B =

KH2PO4

a methanol-acetonitrile-water

50 : 50 : 200 (v/v/v) mixture; C = 0.1 mol L~1 LiCl in a dichloro-methane-ethanol 85:15 (v/v) mixture; D = acetonitrile-water 3: 2 (v/v).

The use of mobile phases containing ^-CD seems to be particularly appropriate for the resolution of racemic S-(1-ferrocenyl-2-methylpropyl)thioethanol and S-(1-ferrocenylethyl)thioethanol (a = 1.43 and 1.18, respectively).

Many noncharged solutes with a carbonyl group close to the stereogenic centre can be resolved on MCTA plates (benzoin, benzoin methyl ether, 2-phenylbutyrophenone, 2- and 3-methylindanone, 2-phyenylcyclohexanone, 2-phenylcycloheptanone and 2-oxazolidone derivatives).

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