C. RIMINGTON 



this suggestion in the reaction mechanism studied by W. Siedel and 

 F. Winkler 12 during the war. These workers discovered a new 

 method for porphyrin synthesis based upon the great reactivity of 

 pyrroles bearing as a-substituents a carbinol and a carboxyl group. 

 Four such units combined, even on standing in neutral methanolic 

 solution, to form a porphyrin, the a-carboxyl groups being simul- 

 taneously eliminated as C0 2 thus : 



H a C- 



Hooc'-'.- 



N 

 H 



H 



N 



'C-jHs H a O' 



•CH^.OHHOOC 



• CjHj C 2 H 5 H 3 C 



h,c-/ ^ /^"X ,/>c,: 



CH 2 OH; 



N 

 H 



H 



N 



OT 2 C 



CH, H 6 C,^ — ^CH, 



<^r 'V? 



>H 2 C 



v-400 a .-4H»0, \ fj 



N 



H 4 C, 



CH, — * H 6 Q 



ALtioporphyrinogen I 



C»H t | HjC 



H,c/\ / CH \ Ac, Hl 



/~N N^v 



/ H \ 



HC CH 



X N N 



H.C,</\ /\>CH S 



CH 



JZtioporphyrin J 



Some combination also took place in such a way as to lead to 

 formation of the series II isomer but, from the point of view of the 

 present discussion, the important fact is that here we have an example 

 of the spontaneous elaboration of a simple pyrrole carboxylic acid 

 into a porphyrin in which the carboxyl carbon, though necessary to 

 the reaction, does not itself appear. 



One might postulate from the present evidence that the glycine 

 first combines with materials in such a way as to give rise to an 

 hydroxymethyl pyrrole carboxylic acid, a porphyrin being subse- 

 quently formed with loss of C0 2 . Whether the [3 side chains are fully 

 elaborated before or after the latter step we do not know but the way 

 seems open to examine these points experimentally. In my laboratory 

 we are endeavouring to obtain confirmation of the elimination of 

 CO 2 from carboxyl-labelled glycine during the biological synthesis. 



248 



