Chemistry 167 



direct oxidation ol ring C - consistently lead to the conclusion that 

 ring B ol colchicine is T-nienibered. 



6.9-9; ^'"i( ^'- ^t will now be evident that the enolone projjerties 

 ol colchiceine derive trom the third ring, namely ring C, and that the 

 structure to be assigned to this ring must also interpret the conversion 

 ol colchiceine into A^-acetyliodocolchinol. This transformation is 

 empirically expressed by 



C,,,H.,;A;N + I ^ C:.OH,,0,NI + [CHO] 



and die colchinol derivative so produced may be formulated as (XIX) 

 which is in harmony with the observation that its methyl ether yields 

 4-iodo-5-methoxyj)hthalic acid on oxidation.'^ •'- Two further links 

 between the structure of the alkaloid and that ol colchinol are known. 

 Cecil and Santaxy-^-^ obtained iV-acetylcolchinol directly by oxidizing 

 colchiceine with alkaline hydrogen peroxide. Again, colchicine (but 



MeO 



Mao's 



/ 



NHAc 



MeO 



')on 



( XIX) 



NH.Vc 



MeO 



MeO 



C02Me 



(XX) 



not colchiceine) is isomeri/cd when heated with sodium methoxide 

 in methanol (Santavy;-^^ Fernholz'''') forming the methyl ester {(lUo- 

 colchicine) of a carboxylic acid (c///ocolchiceine) ; and Fcrnholz^-^ 

 conxerted this acid into A'-acetylcolchinol l)y the standard procedure: 

 RCOTi-^RNH. -^ ROH. The structure of aJJocoUhlnuc is there- 

 fore sec urely fixed as (XX) . 



