Acta Pharm, Suecica 2, 357 (1965) Thin-layer chromatographic and thin-layer electro- phoretic analysis of ergot alkaloids.Relations between structure, RM value and electrophoretic mobility in the cle vine series STIG AGUREll DepartMent of PharmacOgnosy, Kunql, Farmaceuliska Insiitutei, StockhOLM, Sweden SUMMARY A thin-layer chromatographic and electrophoretic study of the ergot alkaloids has been made, to find rapid methods for the separation and identification of the known ergot alkaloids. The mobilities of ergot alkaloids in several useful chromatographic and electrophore- tic systems are recorded. Relations have been observed between structure and R" value in methanol-chloroform on Silica Gel G. A simple, rapid thin-layer electrophoretic technique has been de- vised for separation of ergot alkaloids, and a relation between structure and electrophoretic mobility is evident. Two-dimensional combinations of thin-layer chromatography and thin-layer electro- phoresis and chromatography are described. Numerous paper chromatographic procedures have been published for separation of the ergot alkaloids and their derivatives. Hofmann (1) and Genest & Farmilio (2) have recently listed these systems. The general advantages of thin-layer chromatography (TLC) over paper partition chromatography are well known: shorter time of equilibration and devel- opment, generally better resolution, smaller amounts of substance rc- quired, and wider choice of reagents. Several reports of TLC of ergot alkaloids have been published. In gene- ral, these investigations (2-6 and others) have dealt 'with limited groups of alkaloids, or with a specific problem involving at most a dozen of the 40 now known naturally occurring ergot alkaloids. Some paper chromate- .357 graphic systems using Iorrnamide-treated papers have also been adopted for thin-layer chromatographic use (7, 8). In our investigations on the biosynthesis of peptide-type ergot alkaloids (9), a number of alkaloidal metabolites of both the clavine type and the lysergic acid type could be expected. It was, therefore, necessary to collect a number of chromatographic data on known natural ergot alkaloids in suitable thin-layer chromatographic systems, to make it possible, in a rapid and predictable way, to separate and identify ergot alkaloids, deter- mine their purity or establish the association of radioactivity with a certain alkaloid. Preferably, this method should involve one basic chro- matographic system which, by combination with other systems, would achieve this aim. Since the clavine and the lysergic acid types of ergot alkaloids generally coexist in ergot, and also for other reasons, it would be of general interest to know the distribution of all ergot alkaloids in certain useful thin-layer chromatographic systems. Except for a paper chromatographic investigation by Yamatodani (10), including most ergot alkaloids, no such extensive survey has appeared. It was also decided to investigate whether a rapid, thin-layer electro- phoretic method, suitable for routine use, could be devised. Although it is a common method for analysis of e. g. peptides and proteins; thin- layer electrophoresis has seldom been used for the analysis of alkaloids. Since the clavine-type ergot alkaloids comprise a large group of closely related compounds, they are a suitable group in which to study the rela- tions between structure and chromatographic or electrophoretic mobility. The present study is divided into three parts: 1. Thin-layer chromatography of ergot alkaloids 2. Relations between structure and R" value in the clavine series 3. Thin-layer electrophoresis of ergot alkaloids. Relations between structure and electrophoretic mobility Experimental The ergot alkaloids- used in this investigation were obtained through the courtesy of other laboratories, or were isolated or synthesized by me, in which case, m. p., UV and IR spectra agreed with published data. Ergo- secaline and molliclavine, for which structures have been formulated (1, 11), were isolated in trace amounts by Abe et al, (11) but were no longer available, nor was isochanoclavine- (I), which was recently isolated as a trace alkaloid from rye ergot (12). Although 4-dimethylallyltrypto- ph an is an efficient precursor of the ergo line skeleton, it has not yet been identified as a normal metabolite (1, 11, 31). Nor-agroclavine is, so far, recognized only as a microbial metabolite of agroclavine (18), and the structure of fumigaclavine C has not yet been published. (For for- mulas, see refs. 1, 11-13, 18,24.) 1 Some alkaloids are available from e. g. Koch-Light Labs. Ltd., Colnbrook;Cal- biochem, Los Angeles, and Flulia AG, Buchs. 358 All solvents used were of analytical reagent grade. Chloroform con- tained 1 % ethanol as stabilizer. Mean RF values and, for electrophoresis, relative mobilities (1\1) com- pared with elymoclavine (M = 1.00) were obtained from 5-6 runs of each compound on different plates, and are listed in the tables. The stan- dard deviations were calculated from the individual data. R" = log(1/RF - 1) (20). Thin-layer chromatography Glass plates (20X20 cm) were covered with a 0.25 mm thick layer of Silica Gel G or Aluminium oxide G for thin-layer chromatography (E. Merck AG, Darmstadt) by spreading a well-stirred mixture of 30 g of the adsorbent and 60 ml of destilled water with an applicator (C. Desaga GmbH, Heidelberg). After drying in air for one hour, the plates were activated at 1100 for 30 min, and then stored in a desiccator over silica gel for not more than two days. Cellulose-coated plates were prepared similarly, by spreading a homo- genized mixture of 15 g of Cellulose MN 300 for thin-layer chromato- graphy (Machery, Nagel & Co., Duren, D. B. R.) and 90 ml of destilled 0 water, and drying for 10 min at 105 • Solvents were mixed immediately before use, and 100 ml of the solvent poured on the bottom of the filter paper lined tank (7 X 23 X 23 em). The tank was shaken, and then allowed to equilibrate for 15 min at 25 ± 0.50 before the plates were quickly inserted. Alkaloids were dissolved in suitable organic solvents to contain 0.5-0.7 p,g of alkaloid in the applied 2-3 p,l of solvent, and were spotted 1.5 ern from the lower edge of the plate. Fifteen cm above the origin, a frontline was drawn through the silica layer. For two-dimensional chromatography, a sample was spotted in a corner of a Silica Gel G plate 1.5 em from each side. The chromatogram was developed 15 em, first in solvent MC and, after air-drying for 5 min, in the second direction in solvent DC(Fig. 5) . Solvent systeMs MC. Silica Gel G plates. Methanol-chloroform (2 : 8 by vol.) (4, 9) DC. Silica Gel G plates. Diethylamine-chloroform (1 : 9) (9) L11CA. Silica Gel G plates. Methanol-chloroform-cone, NH3 (20 : 80 : 0.2) EC. Aluminium oxide G plates. Ethanol-chloroform (4 : 96)(4) CBAc. Aluminium oxide G plates. Chloroform-benzene-glacial acetic acid (45 : 45 : 10) (13 ) CM Ac. Silica Gel G plates. Chloroform-metanol-glacial acetic acid (4 : 3 : 3) FEHD. Cellulose plates were impregnated with a solution of 15 % forma- mide and 1 % cone. NH3 in acetone and, after air-drying for 15 min, were 3591 dried in an ovan at 1000 for 90 sec. Solvent: ethyl acetate-n-h eptane- dimethylforrnarnide (250 : 300 : 1) (7). Detection of alkaloids and documentation Fluorescent alkaloids (Table 1) were detected under short wavelength (254 111ft) UV light. A 4 % solution of p-dimethylaminobenzaldehyde in conc. HCI was used to locate all alkaloids. The use of other suitable colour reagents has recently been discussed by Reio (16), and the mecha- nism underlying this colour reaction by Durkee & Sirois (17). The dry chromatogram was sprayed with Neatan Xeu (Merck ) , air-dried, and then taken up on adhesive tape. Thin-layer electrophoresis The high-voltage electrophoresis apparatus and the technique used were similar to those described by Honegger (J ,1). For further details regarding the apparatus, see Samuels son (15). A pyridine-acetic acid buffer (25 1111 pyridine and 7 ml conc. acetic acid in 2 I water, pH 5.6) was used. Alka- loids were spotted 5 ern from the anode side on a Silica Gel G plate, 20)( 20 cm. Since the migration of compounds decreased close to the edges, only the central 12 em of the plate was used. Elyrnoclavine was run as a reference, and electrophoretic mobilities determined relative to ely- moclavine (M = 1.00). The plate was then sprayed with buffer until it became semi-transparent, with a shining surface. A buffer-soaked filter paper wick (Whatman 3 MM) was inserted into each buffer compartment. Contact between the wicks and the thin-layer plate was made with buffer- saturated filter paper strips (Whatrnan No.1). These "were separated from the wicks, dipping into the buffer compartments, hy cellophane, to minimize solution flow (15). On the other two sides of the plate, paper strips were applied to the same thickness as the wicks. On the top, a second glass plate was placed, thus forming a narrow moist chamber. Electrophoresis was carried out at HiOO volts (ca 50 mAl for 45 min, during which time the alkaloids migrated at most 90-100 mm. After 0 drying for 10 min at 100 , the alkaloids were located as previously described. Combined thin-layer electro plioresis and chromatography In a two-dimensional procedure, thin-layer electrophoresis and thin-layer chromatography 'were combined. The sample mixture was spotted i) em from the anode side and 4 cm from the lower edge of a Silica Gel G plate, and sorne known references, e. g. agroclavine and elyrnoclavinc, were spotted 4 em from the upper edge of the plate. After applying buffer pH 5.6, the plate was subjected to electrophoresis for 45 min. The plate was then carefully dried with a fan for a f ew minutes.