Taylor / Robinson Indole Alkaloids

An Introduction to the Enamine Chemistry of Natural Products
1. Auflage 2013
ISBN: 978-1-4832-2174-8
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 162 Seiten

A Course in Organic Chemistry Advanced Section, Volume 27: Indole Alkaloids: An Introduction to the Enamine Chemistry of Natural Products describes the chemistry of selected alkaloids that contain indolic or closely related nuclei. Some five hundred of these compounds have been obtained from about three hundred plants mostly of the family Apocynaceae. This book is composed of 12 chapters that specifically cover the chemistry of the complex indoles. The introductory chapters deal with the origin, isolation, characterization, basic chemistry, and simple derivatives of indole alkaloids. The remaining chapters examine the biogenesis, basic chemistry, stereochemistry, and structure of selected complex alkaloids of various origins. These chapters include tetrahydro-?-carboline, strychnos, iboga, picralima, and eburnamine alkaloids, cinchonamine, quinamine, and ajmaline-sarpagine bases. This text is of great value to organic chemists and researchers.

Autoren/Hrsg.

Taylor, W. I.

Robinson, Robert

Inhaltsverzeichnis

1;Front Cover;1
2;Indole Alkaloids: An Introduction to the Enamine Chemistry of Natural Products;4
3;Copyright Page;5
4;Table of Contents;8
5;Dedication;6
6;NOTE BY EDITOR;7
7;CHARTS;10
8;PREFACE;12
9;INTRODUCTION;14
10;CHAPTER I. SOLATION AND CHARACTERIZATION OF INDOLE ALKALOIDS;18
10.1;GENERAL REFERENCES;21
11;CHAPTER II. THE ORIGIN OF INDOLE ALKALOIDS;22
11.1;SUGGESTED READING;29
12;CHAPTER III. BASIC CHEMICAL CONSIDERATIONS;30
13;CHAPTER IV. SIMPLE DERIVATIVES OF TRYPTOPHAN;42
13.1;The Tryptamines;43
13.2;Physostigmine;46
13.3;The Harmala Bases;50
13.4;Rutaecarpine;55
13.5;Calycanthine;56
13.6;The Ergolines;61
13.7;SUGGESTED READING;64
14;CHAPTER V. THE COMPLEX TETRAHYDRO-ß-CARBOLINE ALKALOIDS;65
14.1;The Yohimbanes;65
14.2;The Yohimbines;73
14.3;C-3 Stereochemistry;73
14.4;The seco Compounds;75
14.5;Burnamicine;77
14.6;Ring . Oxygen Heterocycles;81
14.7;SUGGESTED READING;85
15;CHAPTER VI. THE STRYCHNOS ALKALOIDS;86
15.1;STRYCHNINE;88
15.2;AKUAMMICINE;97
15.3;SUGGESTED READING;99
16;CHAPTER VII. CINCHONAMINE AND QUINAMINE;100
16.1;Cinchonamine;100
16.2;Quinamine;103
16.3;SUGGESTED READING;105
17;CHAPTER VIII. THE AJMALINE-SARPAGINE BASES;106
17.1;Ajmaline;106
17.2;Sarpagine;113
17.3;Vobasine;113
17.4;Voachalotine;114
17.5;SUGGESTED READING;117
18;CHAPTER IX. THE IBOGA ALKALOIDS;118
18.1;Ibogaine;119
18.2;Voacangine;124
18.3;Catharanthine and Cleayamine;124
19;CHAPTER .. THE EBURNAMINE ALKALOIDS;130
19.1;Canthin-6-ones;130
19.2;Eburnamonine;133
19.3;Eburnamine;136
19.4;Vincamine;137
19.5;Schizozygine;138
19.6;SUGGESTED READING;140
20;CHAPTER XI. ASPIDOSPERMA BASES;141
20.1;Aspidospermine;143
20.2;The Mass Spectrum of Aspidospermine;145
20.3;Kopsine;147
20.4;SUGGESTED READING;149
21;CHAPTER XII. PICRALIMA ALKALOIDS;150
21.1;Picraline;154
21.2;EPILOGUE;157
22;INDEX OF PLANT NAMES;158
23;INDEX OF CHEMICALCOMPOUNDS, ETC.;159

Leseproben

CHAPTER I

ISOLATION AND CHARACTERIZATION OF INDOLE ALKALOIDS

Publisher Summary

This chapter discusses the isolation and characterization of indole alkaloids. Many precipitation and chromogenic methods were developed by classical chemist for the isolation of alkaloids. They either depended on the water insolubility and color of complex acid salts or the generation of characteristic colors with oxidizing agents under defined conditions. For indole alkaloids, some color reactions are specific to a particular indolic system and in a very crude mixture, such a test is often more useful than attempting to measure and interpret an ultraviolet absorption spectrum. Once the crude alkaloids have been obtained, separation methods are applied that take advantage of previous experience and modern methodology, such as column, partition, or ion exchange chromatography; countercurrent distribution; and the like. The results of the fractionation can be followed by all or as many of the physical methods as need be brought to bear to the problem. The isolated pure base can be characterized via its melting point, via its optical rotation, via its ultimate analyses, and by the formation of derivatives. The ultraviolet absorption spectrum defines the chromophoric moiety and the infrared spectrum, besides fingerprinting the molecule by its wealth of bands, detects various functionalities, in particular carbonyl groups and hydrogen attached to nitrogen or oxygen. Nuclear magnetic resonance spectroscopy yields information from which the proton topography can be deduced. There is also the mass spectrum; the interpretation of whose line-rich spectrum often allows the entire structure of the alkaloid to be deduced. With the structure of the indole alkaloid largely defined by the use of the above methods, the chemist can operate more meaningfully with small amounts of material to complete the structure proof.

The following remarks, although written specifically with indole alkaloids in mind, are good for alkaloids in general and basically true for any isolation problem. At some time during the workup of a plant extract advantage is taken of that property of the looked for substance(s) which will enable its separation from the other products. For an alkaloid one normally takes advantage of its basicity unless some other incidental property can be effectively used. In its simplest form an extract of the plant in a water immiscible solvent is washed with aqueous acid which upon subsequent basification affords the alkaloids.

This simple and direct method has possible liabilities since the strong acid which may have to be used to get out the weak bases may induce undesirable changes in the alkaloid mixture (e.g. eburnamine, p. 123). Also extraction of the plant with the water immiscible solvent probably would have left behind the quaternary bases, N-oxides, amino acids and perhaps even phenolic bases.

A useful and systematic approach is to make an extraction with petroleum ether to remove fats and waxes keeping in mind that some bases can be extracted with such a solvent and to follow this up with wet benzene. The benzene solution should contain the tertiary bases and washing it with buffered solutions of decreasing pH will yield crude alkaloids divided roughly into groups of similar basic strengths. The aqueous phase resulting from the wet benzene extraction would be expected to contain any alkaloid salts, the N-oxides, quaternary bases, amino acids and perhaps phenolic bases.

A simple version of this scheme of commercial importance is illustrated by obtention of reserpine (p 6·06) from the roots of The ground roots are extracted with benzene which is washed with aqueous acetic acid to remove the strong bases, and concentrated whereupon the reserpine crystallizes out.

Occasionally isolation of a particular alkaloid is facilitated by forming a water insoluble salt, nitric, perchloric, sulphuric and oxalic acids have often been used for this purpose but this does not form part of any systematic procedure except for the removal of water soluble bases from aqueous solution. Thus for quaternary salts picric acid and reinecke salts have been widely used. N-oxides also form water insoluble derivatives with many acids but this problem can usually be dealt with by reduction back to the parent tertiary base which is then soluble in organic solvents.

In order to follow the course of an alkaloid isolation the classical chemist developed many precipitation and chromogenic methods. They either depended on the water insolubility and colour of complex acid salts or the generation of characteristic colours with oxidizing agents under defined conditions. For indole alkaloids some colour reactions are specific to a particular indolic system and in a very crude mixture such a test is often more useful than attempting to measure and interpret an ultraviolet absorption spectrum. Useful colours are generated by ceric sulphate, or in sulphuric acid containing a trace of an oxidizing agent, e.g. ferric chloride (Keller), sodium nitrite (Arnold-Vitali), sodium molybdate (Fröhde) and potassium dichromate (Otto).

For precipitations the most well known reagents are Mayer’s (potassium mercury iodide), Sonnenschein’s (phospho-molybdic acid) and occasionally picric acid. Today these reagents have a new use as detectors in paper and thin layer chromatography.

Once the crude alkaloids have been obtained separation methods are applied which take advantage of previous experience and modern methodology such as column, partition or ion exchange chromatography, countercurrent distribution and the like. The results of the fractionation can be followed by all or as many of the physical methods as need be brought to bear to the problem.

The isolated pure base can be characterized via its melting point, optical rotation (or optical rotatory dispersion curve), ultimate analyses and by the formation of derivatives. All of these measurements were very important up to about 1950 since these were the only means available for comparing compounds. Today many of these pointer readings have diminished in value because more accurate comparisons can be made by a multiplicity of physical methods which sometimes result in a complete proof of structure. The ultraviolet absorption spectrum defines the chromophoric moiety and the infrared spectrum besides “fingerprinting the molecule” by its wealth of bands, detects various functionalities in particular, carbonyl groups and hydrogen attached to nitrogen or oxygen. Nuclear magnetic resonance spectroscopy yields information from which the proton topography can be deduced. Then there is the mass spectrum the interpretation of whose line rich spectrum often allows the entire structure of the alkaloid to be deduced.

With the advent of computers it has become possible to reduce the interpretation of the X-ray diffraction data of a single crystal containing a heavy atom (e.g. the alkaloid iodide, bromide, brosylate) to a routine. This method is absolute and requires no assumptions as to the structure and it will eventually be used by the chemist as naturally as he has accepted all the other aids which have come his way. It has already enriched our knowledge by solving problems for which there was either no chemical method available or simply not enough material for a chemical examination.

With the structure of the indole alkaloid largely defined by use of the above methods the chemist can operate more meaningfully with small amounts of material to complete the structure proof. This can take the form of either partial degradation to or partial synthesis from a known base, which at the same time settle the absolute stereochemistry.

With the structure, stereochemistry and conformation now relatively easy to determine and the degradative process eliminated there remains the challenge of synthesis and it must be by a rapid, high yielding stereospecific (or selective) route. There are as yet few landmarks in this area but it is one to which an increasing amount of attention is being paid.

GENERAL REFERENCES

BUDZIKIEWICZ, H., DJERASSI, C., WILLIAMS, D.H. Structure Elucidation of Natural Products by Mass Spectrometry; I. Alkaloids, Holden-Day, San Francisco, 1964.

DJERASSI, C.Optical Rotatory Dispersion: Applications to Organic Chemistry. New York: McGraw-Hill, 1960.

HAMERSLAG, F.E.The Technology and Chemistry of Alkaloids. New York: Nostrand, 1950.

HESSE, M.Indolalkaloide in Tabellen. Heidelberg: Springer-Verlag, 1964.

JACKMAN, L.M.Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry. London: Pergamon Press, 1959.

MACEK, K., HAIS, I. M., GASPARIC, J., KOPECKY, J., and RABEK, V., , Publishing House of Czechoslovak Academy of Sciences, Prague, 1962.

MATTHIEU, J.P., JANOT, M.-M.Selected Constants IV, Optical Rotatory Power and Alkaloids. London: Pergamon Press, 1961.

NAKANISHI, K.Infrared Absorption Spectroscopy—Practical. San Francisco: Holden-Day, 1962.

NEUSS, N.Physical Data of Indole and Dihydroindole Alkaloids. Indianapolis, Indiana: Eli Lilly and Company, 1961.

NYBURG, S.X-ray Analysis of Organic Structures. New York: Academic Press, 1961.

SCOTT, A.I.Interpretation of the...