78 THE SYNTHESIS OF FATS 



Two molecules of acetic aldehyde then undergo an aldol 

 condensation — 



CH3CHO + CH3CHO = CH 3 CHOHCH 2 CHO 



and the resulting aldol by molecular rearrangement gives 

 butyric acid — 



CH3CHOH CHXHO -> CH 3 CH 2 CHXOOH. 



The conception of making use of aldol condensations for 

 the successive building up of more and more complex aldols 

 by the serial addition of two atoms of carbon was developed 

 by Magnus Levy * and subsequently by Leathes.f Thus the 

 formation of an eight-carbon fatty acid can be explained by 

 the following changes : — ■ 



4CH3CHO = CH3CHOH CH 2 CHOH CHXHOH CHXHO 



which, by loss of four molecules of water, would give the un- 

 saturated aldehyde CH 3 . CH : CH . CH : CH . CH : CH . CHO, 

 from which, by the addition of six atoms of hydrogen and 

 one of oxygen, would be obtained the eight-carbon atom fatty 

 acid CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 COOH, octoic or caprylic 

 acid. An extension of this suggestion is that due to Smedley 

 and Lubrzynska J according to whom pyruvic acid produced 

 by the decomposition of carbohydrate is the starting-point 

 for the formation of fatty acids ; pyruvic acid is known 

 to yield acetic aldehyde by the action of the enzyme car- 

 boxylase, and the aldol condensation of this acetic aldehyde 

 with another molecule of pyruvic acid would yield a five- 

 carbon compound according to the following equations : — 



(1) CH3CO COOH = CH3CHO + C0 2 



Pyruvic acid Acetaldehyde 



(2) CH3CHO + CH 3 CO COOH = CH3CHOH CHXO COOH. 



The latter substance by loss of water would give an un- 

 saturated ketonic acid 



CH 3 CH : CH CO COOH 



which could react in either of the two following ways to give a 

 four-carbon compound. 



♦Magnus Levy: " Engelmann's Archiv," 1902, 365. 



f Leathes : "Problems in Animal Metabolism," London, 1906. 



X Smedley and Lubrzynska: ''Biochem. Journ.," 1913, 7, 364. 



