Acidic and Basic Drugs

The enantiomers of basic ^-blocking drugs can be separated on HPTLC DIOL F254 plates (Merck) with N-CBZ-Gly-l-Pro (or similar chiral agents) in the mobile phase, while the separation of the same drugs, derivatized with (R)-( — )-1-(1-naphthyl)ethyl isocyanate in dichloromethane, has been performed on HPTLC-NH2 F254 plates chemically bonded with N-(3,5-dinitrobenzoyl)-.R-( — )-a-phenylglycine (DNBPG) and eluted with different mixtures of n-hexane/isopropanol.

Interesting separations of racemates with a fi-aminoalcohol structure (i.e. ephedrine and norephedrine, and ^-blockers) can be achieved on MCTA plates after their cyclization with phosgene to form 5-substituted oxazolidinones.

Table 4 Enantiomeric separation of /V-alkyi, A/-carbamyl and A/-formyl amino acids and of dipeptides on Chiralplates

Racemate

hRfia

hRF2

Eluent

Remarks

N-Formyl-t-Leu

48( + )

61( —)

A

A = methanol-water-acetic acid 50 : 50 : 200 (v/v/v).

A/-Methyl-Abu

65

73

D

B = methanol-water-acetic acid 50 : 50 : 30 (v/v/v).

N-Ethyl-Abu

69

72

D

D = acetone-methanol-water 10:2:2 (v/v/v).

N-Methyl-Ala

64

70

D

M = 1 mmol L~ copper (II) acetate, 5% methanol (pH 5.8).

N-Methyl-Asp

58(L)

67(D)

B

Migration distance 13 cm; chamber saturation.

N-Methyl-Leu

49(L)

57(D)

A

Visualization; Ehrlich's reagent for N-carbamylTrp, iodine for

N-Methyl-Nle

68

77

D

N,N-dimethyl-Phe, and ninhydrin for the others.

N-Methyl-Nva

67

76

D

N-Ethyl-Nva

70

74

D

N-Methyl-Phe

50(D)

61(L)

A

N,N-Dimethyl-Phe

55(D)

61(L)

B

N-Methyl-m-Tyr

36

52

B

N-Methyl-Val

65(L)

70(D)

B

N-Carbamyl-Trp

44(L)

55(D)

M

Gly-Phe

57(L)

63(D)

B

Gly-Leu

53(L)

60(D)

B

Gly-Ile

54(L)

61(D)

B

Gly-Val

58(L)

62(D)

B

Gly-Trp

48(L)

55(D)

B

Leu-Leu

19(D, L)

26(L, D)

A

48(D, L)

57(L, D)

B

Ala-Phe

21(D, L)

26(L, D)

A

59(D, L)

65(L, D)

B

Met-Met

29(D, L)

33(L, D)

A

64(D, L)

71(L, D)

B

Asp-Phe-OCH3

50(L, L)

62(D, D)

A

50(L, D)

62(D, L)

A

Many acidic drugs (Figure 2) are resolved as 3,5-dinitroanilyl (DNAn) derivatives on precoated HPTLC-NH2 F254 plates derivatized with R-( - )-1-(1-naphthyl)ethyl isocyanate (Table 8). Although the naphthylethyl chromophore has a high UV adsorptiv-ity, the detection problems found on plates bonded with DNBPG were not observed.

High selectivity coefficients are obtained for un-derivatized acidic drugs on MCTA and diphenyl-F plates eluted with aqueous-organic solutions containing, in the latter case, a chiral macrocyclic antibiotic (vancomycin).

Other pharmaceuticals resolved include bendro-flumethiazide, coumachlor, mephenytoin, oxindanac benzyl ester, warfarin, chlorowarfarin, hexobarbital, oxazepan, lorazepan, norphenylephedrine, hyos-cyamine and colchicine.

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