CHEMISTRY I23 



Emil Fischer enumerated nineteen amino-acids which were to be regarded as the chief 

 hydrolytic cleavage products of the proteins (see E. B. i, 153 et seq., article "Albumin")/ 

 One of these amino-acids, viz. histidine, which in 1907 had not been built up in the 

 laboratory, has now been synthesised (Pyman, /. Chem. Soc., 1911, 99, 1386), and the 

 racemic compound obtained in the synthesis has been resolved into the optically active 

 isomerides. 



Fischer and his pupils have combined amino-acids in a great variety of ways, and 

 have thus prepared a large number of synthetic products, termed polypeptides, the 

 simpler ones being similar to peptones, the more complex ones resembling proteins. 

 The study of these polypeptides, moreover, has led to improved methods of isolating 

 and detecting decomposition products of the proteins. In this direction much work 

 is being done by Abderhalden, who finds that for the purpose of distinguishing proteins 

 partial hydrolysis is preferable to total hydrolysis. The latter treatment applied to 

 different proteins may yield the same amino-acids in equal quantities, without throwing 

 any light on the different ways in which these amino-acids were linked together in the 

 proteins. Partial hydrolysis, however, leaves the amino-acids still associated to some 

 extent. From silk fibroin, for instance, three dipeptides and a tetrapeptide have been 

 successfully isolated in this way (Zeitsch. Physiol. Chem., 1909, 58, 334; 63, 401). 



The constitution of the alkaloids has in some instances been settled by a complete 

 synthesis; as, for example, in the case of laudanosine, the first opium alkaloid to be 

 completely synthesised (Pictet and Finkelstein, Compt. rend., 1909, 148, 925), papaver- 

 ine (Pictet and Gams, ibid., 149, 210), narcotine (Perkin and Robinson, J. Chem. Soc., 

 1911, 99, 775), and berberine (Pictet and Gams, Compt. rend., 1911, 153, 386). The 

 structure of other alkaloids which have not yet been completely synthesised is being 

 gradually elucidated (see, for instance, Perkin and Robinson, J. Chem. Soc., 1910, 97, 

 305; 1912, 101, 1775; Rabe, Ann., 1910, 373, 85; Ber., 1911,44, 2088; Pschorr and 

 KnofHer, Ann., 1911, 382, 50; Wieland and Kappelmeier, Ann., 1911, 382, 306; Pyman, 

 /. Chem. Soc., 1911, 99, 668; Pschorr, Ber., 1912, 45, 2212). 



The hydrolysis of tannin with sulphuric acid indicates that it is a compound of one 

 molecule of dextrose with five molecules of digallic acid, and in confirmation of this result 

 substances resembling tannin in all respects have been prepared synthetically (Fischer 

 and Freudenberg, Ber., 1912, 45, 915). 



Recent research confirms the existence of a close relationship between chlorophyll 

 and haematin (from oxyhaemoglobin). The amorphous natural chlorophyll is the 

 ester of a tricarboxylic acid, termed chlorophyllin, in which two carboxyl groups are 

 esterified by methyl alcohol and phytol respectively, the third probably remaining free 

 (Willstatter and others, Ann., 1910, 378, i, 18; 1911, 380, 148, 154, .177; 1912,300, 269). 

 Reduction of chlorophyll derivatives yields haemopyrrol, w0-haemopyrrol, and phyl- 

 'opyrrol, and it is noteworthy that these compounds result also from the reduction of 

 haematin (Willstatter and Asahima, Ann., 1911, 385, 188. See also Piloty, ibid., 1910, 



377, 3i4)- 



The remarkable progress made in the synthesis of the terpenes (see E. B. xxvi, 

 647 et seq.) bears witness to the value of the Grignard reaction. The synthesis of 

 terpineol has been followed up by the preparation of the d- and /- isomerides. Attempts 

 to convert these active terpineols into the corresponding active limonenes have been 

 unsuccessful; apparently during the elimination of water from terpineol a migration of 

 the double linking occurs and the optical activity disappears (see Chou and Perkin, 

 J. Chem. Soc., 1911, 99, 526). 



The great majority of the naturally occurring members of the terpene group are 

 derivatives of ^-cymene, but all the theoretically possible menthenols and menthadienes 

 of the ortho-series have been synthesised, with the exception of the A 2 -isomerides. 

 All the possible inactive w-menthenols and w-menthadienes of the type of terpineol 

 and dipentene have been prepared synthetically, including sylvestrene (Perkin and 

 others, /. Chem. Soc., 1907, 91, 480; 1908, 93, 1876; Proc. Chem. Soc., 1910, 26, 97). 



Certain menthadienes are found to be characterised by an abnormally high boiling 



