Regularities Of Adsorptive Separation And Purification Of Alkaloids

Alkaloids are a group of natural organic compounds containing mostly basic nitrogen atoms in a heterocyclic ring and most of them are alkaline. Alkaloids represent one of the most widespread classes of natural products, which derive from more than100botanical families including cryptogams, phanerogams, mono-and dicotyledons. Alkaloids exhibit a range of biological and pharmacological activities such as anti-tumor, anti-bacterial, pain-relief and antihypertensive; many of them are the main bioactive ingredients of medicinal plants and traditional Chinese medicine, and some of them have been directly used as natural medicines in several clinical applications. Nowadays, alkaloids are still the potential natural products in drug discovery, and extraction, effective separation and purification of alkaloids from natural resources remain important topics in natural products research and development. However, alkaloids generally exist in multicomponent mixtures with a very low concentration in natural resources. Furthermore, the structural diversity and alkalinity of alkaloids make their separation and purification directly from plant extracts a very challenging task.Adsorption is one of the most widely used and the most effective methods for alkaloids separation and purification. However, the existing separation processes of alkaloids on commercial adsorbents were mostly used for one or two alkaloids isolation or total alkaloids purification from natural plant extracts; these processes are only applied to a few limited plant resources, and high adsorption capacity and selectivity are two main problems of commercial adsorbents. Therefore, study on adsorption of alkaloids on different commercial adsorbents and development of effective adsorbents for purification of alkaloids from aqueous solutions are very important. Focus on the adsorption separation and purification of alkaloids, the research works were summarized as follows:1Extraction of total alkaloids from Eupatorium lindleyanum DCThrough single-factor experiment, the extraction process of total alkaloids from Eupatorium lindleyanum DC was studied, and the optimal conditions of extraction were obtained as follows:the concentration of ethanol90%, the concentration of acetic acid0.5%, the ratio of solvent to material8and extraction times2with1h per time. The yield of total alkaloids from Eupatorium lindleyanum DC was0.52%at those conditions.2Hypercrosslinked poly(styrene-co-divinylbenzene) resin as a specific polymeric adsorbent for purification of berberine hydrochloride from aqueous solutionsA hypercrosslinked poly(styrene-co-divinylbenzene) resin (TEPA) was synthesized, characterized and to be used as a specific polymeric adsorbent for separation of berberine hydrochloride as an alkaloid model compound from aqueous solutions. Three organic compounds of different molecular sizes (2-naphthol, berberine hydrochloride and Congo red) were chosen as target molecules to elucidate the molecular sieving effect of the TEPA resin. The adsorption capacity of2-naphthol on TEPA was the largest, the adsorption capacity of berberine hydrochloride was much smaller while that of Congo red was the smallest among the three adsorbates, suggesting a potential molecular sieving effect of the TEPA resin. The adsorption kinetic data indicated that the adsorption of2-naphthol on the TEPA resin was the fastest, adsorption of berberine hydrochloride was much slower while that of Congo red was the slowest. The separation capability of the TEPA adsorbent for purification of berberine hydrochloride was well demonstrated in a dynamic adsorption experiment, and the purity of berberine hydrochloride increased from66.7%to99.4%.3Separation and purification of alkaloids on macroporous resinsThe adsorption properties (equilibrium, kinetics and column breakthrough) of five alkaloid model compounds (quinine, berberine hydrochloride, ligustrazine hydrochloride, colchicine and matrine) on26macroporous resins were studied. Generally, the resins with a low polarity and a high surface area offered high adsorption capacities for all alkaloids, while the pore size of the resins should also be considered during the selection of proper resins for certain alkaloids. Among all the resins, non-polar (HPD100B and HPD300) or weakly polar (AB-8and HPD722) resins were suitable for the adsorption of all the five alkaloid compounds. In dynamic adsorption experiment on HPD300, a competitive adsorption phenomenon happened between the five alkaloids in the mixture solution.4Ordered mesoporous carbon as a superior adsorbent for purification of alkaloids in aqueous solutionsAn ordered mesoporous carbon was synthesized, characterized, and used as an effective adsorbent for purification of alkaloid compounds from aqneous solutions for the first time. Berberine hydrochloride, colchicine and matrine were selected as the model compounds to evaluate the adsorption properties of the ordered mesoporous carbon for alkaloids. The ordered mesoporous carbon displayed a great adsorption capacity of the alkaloids (berberine hydrochloride, colchicine and matrine) which were more than double the adsorption capacities of these compounds on two commonly used commercial resins (HPD300and HPD100B) at a similar condition, and the adsorption equilibrium could be achieved in a very short time. Great adsorption capacity and high adsorption rate indicated the ordered mesoporous carbon to be a promising adsorbent for adsorption and purification of different alkaloids from plant extracts.