Hhe Synthesis of Compounds Related to Colchicine A thesis submitted for the degree of Doctor of Philosophy at the University of Glasgow George. 1. Buchanan, B.Sc, Department of Chemistry University of Glasgow. July 1954. ProQuest Number: 13838739 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13838739 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 Preface. The author wishes to express his gratitude to Professor J. W. Cook, P.P.S., and Dr. J. D. Loudon, for their guidance, and advice in the work described. He is also indebted to the Carnegie Trust for the Universities of Scotland, for the award of a Research Scholarship. Because of war-time demands, this scholarship was held for only one year, and covers Part 1 of this thesis. There is an interval of about four years between the work described in Parts I and II, and this has necessitated a somewhat lengthy Historical Introduction to Part II. The micro-analyses, unless otherwise acknowledged were carried out by Mr. JVM . L. Cameron and his staff to whom the author is also grateful. (iii} IHDEX page PART I . Attempts to synthesise. De amino- colchinol Methyl Ether .... 1 Historical Introduction ......... 2 Theoretical Discussion .... 14 Experimental .... -...... 24 PART II. Investigations of rings B and C in Colchicine ...... 38 Historical Introduction ........ 39 Theoretical Discussion ....... 52 Experimental ..... 63 PART: III. Iso—tropolones ..... 81 Historical Introduction ........ 82 Theoretical Discussion ........ 95 Experimental ...... 109 Publications • ............................ „ 125 Bibliography ...................... 126 PART I Attempts to s3r1.1tb.esise DeamLinocolchin.ol Methyl Ether. Historical Introduction The seeds and corms. of the Autumn Crocus, or Meadow Saffron. (Colchicum Autumnale, Linn.) yield an alkaloid Colchicine, together with a number of related substances (X). Although known from earliest times as a specific for gout, later interest in colchicine centred on its property of arresting cell-division, and recent chemical interest in the alkaloid has been stimulated by the claim (2) that it caused regression of tumours in mice. Colchicine, originally isolated in 1820, (3) was only obtained in a, pure state in 1915, by Clewer, Green and Tutin (4). More recently, chromatography has been used (5) to obtain the pure alkaloid of m.p* 15?°, [a]*7 , - 120.7°. The chemical investigation of colchicine was begun by Zeisel (6), who showed that it had the molecular formula C22H2,-0gM, anE 011 ® i U hydrolysis, it lost methanol, yielding an acidic product - Colchiceine - of formula C ^ E ^ O G21H2205M^00E35 — > c 21h 22o 5u (o h ) 5 In. contrast to .colchicine, this hydrolysis product gives a green colouration .with aqueous ferric chloride, and forms a copper salt (7). Hydrolysis of colchiceine under less mild conditions gives acetic acid, and an amphoteric substance — trimethyl colehicinic acid - C19H21° j-He Zeisel was able to show by exhaustive methylation of this latter product, that the nitrogen was present as a primary amino group, and formulated the second hydrolysis step as follows, 0 ^ 0 4 . (Off) CHHOOCHj) ------ ClgH1804 (0H)(HH2) Analysis showed also the presence of three methoxyl groups, and these observations led Zeisel to assume that colchicine was the methyl ester of an aeetamido acid. This allocation of the oxygen atoms was apparently supported by the fact that neither colchicine nor its .hydrolysis products gave carbonyl derivatives. A ketonic derivative, oxy-colchicine was obtained (14) by oxidation of the alkaloid and revealed the presence of a methylene group in the molecule, whose partial structure was apparently I (CH50)5.C14H7 .(c h 2)(e e .o o c h ^)(c o o c h ^) I This formulation was re-examined and modified by Windaus (8), in a series of investigations (9) which eventually led him to propose the following structure for the alkaloid. o He; showed that trimethyl eolchicinic acid could readily he acylated, yielding 0,H—diacyl derivatives. This, he pointed out, was indicative of an enol rather than a carboxyl structure, and this concept is supported by the green colouration shown by colchiceine and trimethyl colchicinic acid with aqueous ferric chloride. Yfindaus therefore postulated a tautomeric a,ldehyde hydroxy— methylene structure to account for the acid oxygen function of colchiceine, and supported it with three pieces of evidence:- a) On treatment with bromine water (10) colchiceine is converted into an acid with the same number of carbon atoms 020H22°5E * (GH°) * G20®l9Br3*05^* (G02H ^ The 0 ,F—dibenzene- sulphonyl derivative of trimethyl colchicinic acid exists in two distinct forms. This cannot be explained on a carboxylic acid formula, but may be readily accommodated in a hydroxy—methylene formula, where two. stereo­ isomers II may be expected. H 0*S0o»Ph \ y \ y 2 js = c a = 0 \x0S02*Ph ^ ^SI II c) Colchiciene reacts with iodine and caustic potash, to give a phenolic product, F—acetyl iodocolchino1, in which the —GEO group is replaced by iodine C20E22°5.3Sr* ^GE°) — > c 20h 2205n i b This reaction may he compared with that of hydroxy- methylene camphor with bromine and KOH (ll) or iodine and KOH (12). In these latter cases, the hydroxy- meth.yl.ene group is removed, and a halogenated camphor is obtained. Windaus showed moreover (13) that under identical conditions, 2-hydroxy~l-naphthaldehyde III, (but not m-hydroxy aldehydes) gave the iodophenol IT These analogies, led Windaus. to postulate for colchiceine the phenol-aldehyde, hydroxymethylene-fcetone formula T, although he appreciated its shortcomings. T In particular, it does, not account for the absence of carbonyl properties in colchicine or its. hydrolysis products;. The FLndaus partial Y may be re-written as Ya, in the light of Zeisel!s work, and it therefore (c h 3o )3 ^ Va E = IT; R'= CHO - CB Vb E = H; R'= X •2 CHjCOHS - ^ CgH To E = CH^; E '= X Yd E = OE^;R'= H Vi XX J follows, that IT—acetyl iodocolchinol is represented by Y b , and its methyl ether by Yc. This latter substance, may be reduced to UF—acetyl, colchino 1 methyl ether Yd. The structure' of E—acetyl iodocolchinol methyl ether was supported by its oxidation to an iodomethoxy phthalic acid (1.6) , which Grewe (15) subsequently identified as: YI. The oxidation of colchicine to YII (16) served to; locate: the remaining three methoxy groups, and revealed the presence of another ring. 8 When the oxidation of colchicine is preceded by alkali- fusion, two non—methoxylated acids VIII and IX are obtained, and although open to re—interpretation in the light of the modern tropolone formula, this was taken by Windaus as evidence of a third, central, ring in the colchicine molecule. He was also able to show (9) that the tricyclic ring system was of the phenanthrene type. Hoffmann deamination of coldhinol methyl ether gave a tetramethoxylated hydrocarbon, deamino colchinol methyl ether, which on demethylation and zinc dust distillation yielded 9~methyl phenanthrene X (17)• Prom its degradation to X, Windaus, assumed a partial formula XI for colchiceine and XII for colchicine with the proviso that the substituents of ring C may require to be interchanged. Orientation of the Cttofs o remaining substituents was accompanied (9) in the following manner:- a) From the oxidation of IT—acetyl colchinol methyl ether, 4-methoxy phthalimide XIII was isolated. This demonstrated that the nitrogen atom was situated adjacent to ring C. b) Since Zeisel (14) had previously demonstrated the presence of a methylene group in the molecule, the methyl group was assumed to be located on the same carbon atom as the nitrogen. c) Careful oxidation of F-benzoyl trimethyl colchicinic acid gave two degradation products whose compos­ itions indicated that only 3 carbon atoms had been lost, and whose properties suggested a lactone and an anhydride respectively. They were formulated as XIV (F-benzoyl colchide) and XV 10 (H-benzoyl colchinic anhydride) in the light of structure XII. This orientation of the methoxy groups follows from a further degradation of the anhydride XT. Reduction of the olefinic double bond, and simultaneous hydrolysis of the anhydride, • gave a dicarboxylic acid (Cg^Hg^OgH) which on d&methylation with HI lost one molecule of 00^, and yielded a lactone. The formation of a lactone in such a molecule is only possible y/hen both groups are in the peri—positions (18) , and Yfindaus accordingly formulated the lactone as XYI. With the orientation of the substituents now complete, Windaus was able; to formulate colchicine as XTII or XTIII, and colchiceine as XIX or XX. It followed therefore ■NViOoW O XVI] VvTd ; £ * 5oT : that K-acetyl iodocolchinol methyl ether, must he represented by XXI, colchinol methyl ether by XXII, and deaminocolchinol methyl ether by XXIII. N.XH1 Concluding his notable examination of the alkaloid Windaus investigated its reduction. The product, erroneously described by him as an octahydro-derivative, was later shown by Bursian (19) to be a hexahydrocolchicine retaining a resistant double bond. In contrast to colchicine, this substance contained no readily hydrolysabl methoxy group, and although this provided no direct support for the Windaus formula, it was compatible with it* Windaus was nevertheless dissatisfied with this colchicine formula for a number of reasons (9). These may be summarised as follows a) It does not readily account for the formation of oxalic and succinic acids in certain oxidations (9)* h) Neither colchicine nor colchiceine gives carbonyl derivatives and colchiceine (XIX or XX) which should readily isomerise to a phenolic aldehyde, can be reconverted (6) by methylation, to the readily hydrolysed methyl ether (colchicine).