Introduction

In the synthesis of medicinal drugs and agrichemical fields, synthetic compounds with optical activity are continuing to gain more attentions. These compounds can show the same physical chemical properties, but show different biological activity.

It has been reported that using only one enantiomer of the optical isomer can enhance the medicinal effects and reduce the side effects when the biological activity varies between the enantiomers.

Our Methods Scouting System makes it simple for users to search and select the appropriate measurement conditions using various solvents and columns for both chiral and achiral separations.

Supercritical fluid chromatography (SFC) is well known for quick separations, easy solvent replacement, easy sample treatment after preparation, decreasing solvent cost over HPLC and simple scale-up from analytical to preparative.

In this article, method scouting of bupivacaine, used as local analgesic, with three modifiers which diethylamine (DEA) was added to for addition agent and six columns is carried out by using SFC system and Method Scouting Program.

SFC method scouting system

Experimental

Experimental Condition
Column:   CHIRALPAK IA, IB, IC, ID, IE and IF/SFC (i-CHIRAL 6), (4.6 mmI.D. x 150 mmL, 5 µm)
Eluent:   CO₂/modifier (75/25)
Modifier:  1) methanol + 0.4% diethylamine, 2) acetonitrile/ethanol (80/20) + 0.4% diethylamine, 3) methyl tert-butyl ether(MTBE)/ethanol (80/20) + 0.4% diethylamine
Flow rate:   3.0 mL/min
Column temp.:   40 ̊C
Wavelength:   UV: 220 nm, CD: 230 nm
Back pressure.:  15 MPa
Injection volume:   5 µL
Standard:   1.0 mg/mL bupivacaine in ethanol/acetic acid (90/10)

Structure

Schematic diagram

1: CO₂ Cylinder, 2: CO₂ pump, 3: Modifier solvents, 4: Solvent switch valve, 5: Modifier pump, 6: Stop valve, 7: Mixer, 8: Pre-heat coil, 9: Autosampler, 10: Column oven, 11: Switching valve, 12: Columns (i-CHIRAL 6), 13: PDA detector , 14: Circular dichroism detector, 15: Back pressure regulator, 16: Chromatography data system

Keywords

Bupivacaine, SFC, Method Scouting Program, i-CHIRAL 6, Chiral separation

Results

Figure 1 and 2 show the results of Method Scouting by UV (PDA) detector and CD detector. This view provides easy viewing of all screening conditions and quick determination of the best for further optimization if needed.

Figure 1. Result of Method Scouting (UV detector)

Figure 2 Result of Method Scouting (CD detector)

Table 1 shows the degree in separation of bupivacaine. As shown in the table, MTBE/ethanol with 0.4 % DEA and CHIRALPAK IA is suited to this measurement.

Table 1  Degree in separation

N.S.: Not Separated