Cent. Eur. J. Chem. • 10(3) • 2012 • 802-835 DOI: 10.2478/s11532-012-0037-y Central European Journal of Chemistry Analysis of alkaloids from different chemical groups by different liquid chromatography methods Review Article Anna Petruczynik Department of Inorganic Chemistry, Medical University of Lublin, 20-093 Lublin, Poland Received 29 October 2011; Accepted 27 January 2012 Abstract: Alkaloids are biologically active compounds widely used as pharmaceuticals and synthesised as secondary methabolites in plants. Many of these compounds are strongly toxic. Therefore, they are often subject of scientific interests and analysis. Since alkaloids - basic compounds appear in aqueous solutions as ionized and unionized forms, they are difficult for chromatographic separation for peak tailing, poor systems efficiency, poor separation and poor column-to-column reproducibility. For this reason it is necessity searching of more suitable chromatographic systems for analysis of the compounds. In this article we present an overview on the separation of selected alkaloids from different chemical groups by liquid chromatography thus indicating the range of useful methods now available for alkaloid analysis. Different selectivity, system efficiency and peaks shape may be achieved in different LC methods separations by use of alternative stationary phases: silica, alumina, chemically bonded stationary phases, cation exchange phases, or by varying nonaqueous or aqueous mobile phase (containing different modifier, different buffers at different pH, ion-pairing or silanol blocker reagents). Developments in TLC (NP and RP systems), HPLC (NP, RP, HILIC, ion-exchange) are presented and the advantages of each method for alkaloids analysis are discussed. Keywords: Alkaloids • Thin layer chromatography • High performance liquid chromatography • Normal phase system • Reversed phase system © Versita Sp. z o.o. 1. Introduction they are often subject of scientific interests andanalysis. Since alkaloids are basic compounds that appear in Most of naturally occurring substances in their structure aqueous solutions as ionized and unionized forms, they have one or more acidic or basic groups. Such are difficult for chromatographic separation for peak compounds appear widely in different areas, such as the tailing, they have poor system efficiency, poor separation environment, food, plant extracts, biological fluids, and and poor column-to-column reproducibility. Reversed- drugs [1,2]. Therefore, it is of crucial importance to develop phase (RP) chromatography continues to dominate efficient methods for the analysis of these compounds applications of high-performance liquid chromatography in several domains such as clinical analysis, quality (HPLC). The majority of silica based stationary phases control, therapeutic monitoring, toxicological analysis, are produced by reacting porous silica particles with an and metabolism studies. Among these compounds appropriate silane. Silanol groups (-Si-OH) on the silica are alkaloids, which are weak organic bases. Alkaloids gel surface are bonded in this reaction but steric effects are pharmacologically active compounds widely used prevent the reaction of only part of all the silanols. Further as pharmaceuticals and synthesised as secondary reaction with a short silane (endcapping) eliminates metabolites in plants. Many of these compounds are the most accessible silanol groups remaining from the strongly toxic. For diagnosis and prognosis of such initial bonding but typically does not substantially alter poisonings, analytical methods for detection and the total concentration of unreacted silanols. These quantification of the respective toxic alkaloids are residual silanols can then interact with basic compounds, required in clinical and forensic toxicology. Therefore, frequently leading to inferior separations, peak symmetry * E-mail: [email protected] 802 A. Petruczynik Analysis of alkaloids from different chemical groups by different liquid chromatography methods and systems efficiency [3]. Protonated basic compounds are regarded as rich sources of tropane alkaloids. The can interact with residual silanol groups of the stationary principal alkaloids of medicinal interest in this group are phase, as shown in the equation: scopolamine and hyoscyamine which are anticholinergic agents in parasympathetic nervous system and they are XH+ + SiO-Na+ ↔ Na+ + SiO-XH+ (1) used as mydriatics and spasmolytics. Phenethylamine alkaloid group is derived Because of that ionic analytes’ retention mechanism biosynthetically from the amino acids tyrosine and is mixed and composed of ion-exchange mechanism with phenylalanine. Alkaloids belonging to phenethylamine the show kinetics and mass transfer and hydrophobic derivatives constitute an important class of natural interactions with much faster kinetics and mass transfer. products due to their structural similarity to many It gives rise to peak tailing [4]. For this reason, it is neurotransmitters. Alkaloids from the group act as necessary to search for more suitable chromatographic stimulants (ephedrine) or hallucinogens (mescaline). systems for analysis of theses compounds. A great Ephedra alkaloids are generally not used alone, but variety of analytical techniques have been applied rather as part of herbal formulas, and are known to the determination of different alkaloids, and liquid to induce pharmacological effects beyond their chromatography is the most frequently used method sympathomimetic activities such as anti-inflammatory, nowadays. The so-called silanol effect on silica based anti-anaphylactic, anti-microbial, anti-histaminic, and stationary phases has still been one of the major topics hypoglycemic effects. Ergot alkaloids are secondary of chromatographic studies even after the development metabolites produced by fungi of the species Claviceps. of advanced stationary phases that were supposed to Toxic effects after consumption of contaminated grains provide symmetrical peaks for basic compounds. have been described since mediaeval times. Colchicine is currently being investigated for potential use as an anti-cancer drug. 2. Occurrence and medical Isoquinoline alkaloids, biogenetically derived from significance of some alkaloids tyrosine, represent a manifold class of alkaloids within the plant kingdom. Isoquinoline alkaloids are spread Indole is an aromatic heterocyclic organic compound. It mainly in the Papaverales, Rutales, Ranunculales, has a bicyclic structure, consisting of a six-membered Geraniales, Plumboginales, Myrtiflore and Rosales benzene ring fused to a five-membered nitrogen- species. Among them benzylisoquinoline alkaloids form containing pyrrole ring. Indole alkaloids are biogenetically an important group with different potent pharmacological derived from tryptophan. These alkaloids contain two activity, including analgesic compounds of morphine, nitrogen atoms, one of which is contained within the antitussives of codeine and noscapine and anti-infective five-membered part of indole nucleus. agents of berberine, palmatine, and magnoflorine. Indole alkaloids constitute an important class of Papaverine serves as muscle relaxant. Thebain is natural products which include a large number of worked up by pharmaceuthical industry to produce biologically important substances such as antitumor semi synthetic compounds such as the analgesic alkaloids (vinblastine, vincristine, ajmaline and oxycodone and the opiate antagonists naloxone and reserpine), cardioarrithmic alkaloid (ajmalicine) the naltrexone. Opium containing isoquinoline alkaloids: blood pressure lowering substances (reserpine), and morphine, codeine, noscapine, papaverine, tebaine, hallucinatory lysergic acid and its derivatives. Some laudanozine, retykuline has strong narcotic properties indole alkaloids are strongly toxic (strychnine), or are and demonstrates analgesic, spasmolytic, antitussive psychoactive substances (psylocibine, bufotenin). and obstructive properties. Tropane alkaloids are an important class of Quinoline alkaloids are based on a bicyclic system in structurally related compounds having in common the with benzene and a pyridine ring are fused together. Most azabicyclo[3.2.1]octane-3-ol skeleton, with usually of them occur in the plant family Rutaceae, especially are estrified with various organic acids: (-)-S-tropic, rute. Quinoline alkaloids have also been identified in apotropic, cinnamic, tiglic, angelic, isovaleric and members of Malvaceae, Acanthaceae, Saxifragaceae α-truxillic. and Zygophyllaceae families. Cinchonidine and quinine Tropane alkaloids mainly occurs in Solanacae, from the bark of the cinchona tree (Cinchona officinalis) Erythroxylacae and Convolvulacae plant families, but are well known for their antimalarial properties. they occur also sporadically in a number of other families The structures of pyridine alkaloids contain a e.g. Proteaceae, Rhizophoraceae plants. Genuses pyridine ring together with a pyrrolidine ring (in nicotine) Atropa, Datura, Duboisia, Hyoscyamus and Scopolia or a piperidine unit (in anabasine), the latter rings arising 803 804 A. Petruczynik Analysis of alkaloids from different chemical groups by different liquid chromatography methods from ornithine and lysine respectively. The alkaloids are salts. Samples containing a large number of water naturally occurring in the solanaceous family. Nicotine, soluble compounds (e.g. phenols, tannines) should be the main alkaloid in the group, in small doses can act as extracted with organic