Capillary zone electrophoresis

Capillary electrophoresis is suitable for use to separate a wide spectrum of both large and small biological molecules. This method was used for analysis of opium alkaloids such as thebanine, codeine, morphine, papaverine and narcotine.

2.9.4. Choice of method and confidence

There exists a long list of different methods of quinolizidine alkaloid analysis (Table 21). These methods are of a chemical and biological nature. The development of methods of alkaloid analysis has been a long and difficult process.

Table 21 General characteristics of the methods and techniques of quinolizidine alkaloid analysis

Table 21 General characteristics of the methods and techniques of quinolizidine alkaloid analysis

Method of Technique

Nature of Method

Kind of Measurements

Sensitivity

Iodine

ch

qual

y/n, c

Taster

bio

qual

y/n, nc

Seed colour

bio

qual

y/n,nc

DRG

ch

qual

y/n, nc

Fluorescence

ph, ch

qual, quant

y/n, nc

Calorimetry

ph, ch

qual, quant

1 Mg, c

Photometry

ph, ch

qual, quant

1-50 Mg

Electrophotometry

ph, ch

qual, quant

1-50 Mg

Spectrophotometry

ph, ch

qual, quant

1-50 Mg

PC

ph, ch

qual, quant

y/n, ±1 mg

GLC

ch

qual, quant

1 Mg, c

GLC/MS

ch

qual, quant

1 Mg, c

HPLC

ch

qual, quant

1 Mg, c

NMR

ph, ch

qual, quant

±0.017%

X-Ray, RTG

ph, ch

qual, quant

±0.04%

ELISA

bio

qual, quant

y/n, 0.001%

RIA

bio, ph

qual, quant

y/n, 0.001%

SPA

bio, ph

qual, quant

y/n, 0.001%

Abbreviations: ch - chemical; bio - biological; ph - physical; qual - qualitative; quant - quantitative; y - yes alkaloid exists; n - no alkaloid absent; c - confident; nc - non-confident.

Abbreviations: ch - chemical; bio - biological; ph - physical; qual - qualitative; quant - quantitative; y - yes alkaloid exists; n - no alkaloid absent; c - confident; nc - non-confident.

Each method has its drawbacks. The various methods for the determination of alkaloids are very diverse, and the results of measurements are not comparable. This is a particular problem when plant material is being compared.

A problem of great importance is the isolation of alkaloids. Traditionally, very strong solvents have been used. This presents some difficulties connected with the confidence with which the results can be treated. The isolation of all alkaloids from the sample, and the purity of this isolation, is also a significant problem.

A further problem which must be resolved is the resistance of quinolizidine alkaloids to other amines and nitrogen compounds during the analysis. The general conclusion is that a perfect method of alkaloid analysis does not exist. Therefore, the explanation of results in the light of the above-mentioned factors is vital in each case.

The history of the use and development of methods of analysing quino-lizidine alkaloids shows a move away from the deployment of iodine towards the use of complicated biological processes, such as antialkaloid antibody and enzymatic processes. It seems to be necessary to incorporate biological methods of alkaloid analysis into the system of analytic-chemical monitoring used in modern laboratories.

2.9.5. Chemical modification of alkaloids

Chemical modification is a process in the change of the structure, skeleton, configuration, moiety groups, biosynthetic ability or form of a compound. Modification is connected with structural changes, including the changes in bioactivity of alkaloids214. By chemical modification, many medicines may be developed for the pharmacological market.

Modification of alkaloids can be considered in three aspects: chemical, biochemical and molbiological. Mechanical changes (chemical) cover structural alterations in all possible parts of compounds. Biochemical changes are connected with the modifications of enzyme activity, while molbiological changes cover biofactor manipulation inside the alkaloid. The latter is a new approach to the modification of alkaloids. The modification of an enzyme and its transfer to an alkaloid molecule is currently a growing research area. Such a modification can be achieved by changes in alkaloids directly, or by changes in their precursors, postcursors or connected proteins. These changes remain possible, but very challenging in alkaloid research. He et al.298 and Teng et al.299 300 have reported on chemical modification of tryptophan enzymes, which also have potential significance for alkaloid research and modifications. Similar studies have also been carried out by Masuda et al.301 in Japan and by Januszewski et al.302 in the USA. Phenylalanine enzymes have been modified as well 303. Moreover, some solvent-stabilized Pt (2.3-2.8 nm) and Pd (83.7-3.8 nm) nanoparticles can accelerate and modify alkaloids, as in the case of Cinchona alkaloids304. Krasnov et al.305 have reported on chemical modification of plant alkaloids, and especially the reaction of cotarnine with bifunctional NH- and CH-acids. In this research, substituted 1,2,3,4-tetrahydroisoquinoline systems were prepared by the reaction of cotarnine with the NH- and CH-acids methyl- and acyl derivatives of pyrazole and 1,3-dicarbonyl reagents. According to Krasnov et al.305, bifunctional pyrazole nucleophiles can deliver substitution products in the N atom, methyl or acyl group, depending on the structure and reaction conditions.

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