A . F.REECHAW
3262 [ C O N T R I n U T I O N FROM 'I'IIE
CFIEMIC.41,
79
DIVISIONO F IUDUSTRIAL CHEMISTRY, COMMOXlVEALTII SCIENTIFIC INDUSTRIAL RESEARCH ORGASIZATION]
P H Y S I C S SECTION, ASD
Tosyl-a-amino Acids.
Val,
11. The Use of the Acid Chlorides for Peptide Synthesis in the Presence of Aqueous Alkali BY A. F. B E E C I L ~ RECEIVED OCTOBER 15, 1956
Degradation of those tosyl-a-amino acid chlorides in which the side chain is strongly electroii-releasing proceeds inore rapidly than peptide formation (with glycine) in strong aqueous alkali. To inhibit degrarlntion, the alkalinity milst h e reduced t o n level at which coupling is slow. Hydrolysis OF the acid chloride then interferes.
tained in soyo yield. When solid tosyl-DiAanyl chloride was added to a solution of glycine in aqueous sodium hydroxide, efferverscetice was apparent as the chloride dissolved and the odor of acetaldehyde became evident, but the coupling product was, tos.SHCRR'COCI OH- --+tos.SHa + RR'CO $- CO C1again isolated in 8OyOyield. TosyI-~-leucylchloride is 99(;7, degraded by cold Evidence was presented'" consistent with the postuRl.'henthis compound lates that, for such decomposition to occur, the aqueous sodium hydroxide. tosylated acid chlorides must be capable of forming was substituted for tosyl-DL-alanyl chloride under a sulfonamido anion, tos.\;CRR'COCl, and must either of the foregoing conditions, a different result carry an electron-releasing side chain a t the a- was obtained. Effervescence was more pronoucced carbon atom. It was apparent that this reaction and no coupling product could be isolated. Tosylwould need to be taken into account if the suscepti- m-valyl chloride, which is also 9 9 5 degraded b y ble compounds were to be used for peptide synthe- cold aqueous sodium hydroxide, la reacted similarly ses in basic aqueous media. Some experiments de- to the leucyl compound. Addition of tosyl-DL signed to test the extent of interference with the valyl chloride to the solution of glycine in aqueous peptide forming reaction mere, therefore, carried sodium hydroxide resulted in evolution of 60% of the theoretical quantity of carbon monoxide m c l p out. It was shown readily that where the tosylamino toluenesulfonamide was isolated from the solution. These results may be interpreted as folIows. A s acid chloride is not degraded, coupling with a second amino acid dissolved in aqueous alkali pro- already has been shown. when tosyl-a-amino acid ceeds smoothly. IJrhen tosyl-L-prolyl chloride chlorides capable of sulfonamido anion formation was caused to react with L-hydroxyproline under are treated with aqueous alkali, both hydrolysis these conditions, the tosylated dipeptide was ob- and degradation occur. Degradation predomitained in excellent yield. In tosyl-L-prolyl chloride nates where the a-carbon atom bears an electronthe nitrogeh is tertiary so t h a t sulfonaniide salt releasing side chain and predominates increasingly formation is not possible.2 Under similar condi- as the inductive power of the side chain increases. tions tosylglycyl-L-proline was prepared, with tosyl- R'hen the aqueous alkali contains ;i secon,d aii~iiio glycyl chloride as the acylating agent. Although acid, a third reaction competes, namely, attack on this chloride is capable of conversion to the sulfon- the acid chloride function by the amino group to amido anion, no side chain is present and degrada- form a peptide bond, Gnder strongly alkaline conditions, t h e second amino acid is almost wholly tion is slight.'" Tosyl-Dt-alanyl chloride is degraded by cold in the anionic form and coupling proceeds more rapl aqueous sodium hydroxide to the extent of %yoas idly than hydrolysis. It-ith t o s y l - ~ ~ - a l a n ychlomeasured by the amount of carbon monoxide ride, whose methyl side chain is only weakly elecevolved. ': This compound in the L-form was used tron releasing, coupling is also faster than degradaby Schonheimer3 for peptide synthesis, his tech- tion ; but with tosyl-~-leucyl and toSyl-DL-valyI nique being to shake a benzene solution of the chlorides, which carry the more strongly inductive chloride with a solution of the second amino acid in isobutyl and isopropyl side chains. resjwctivcly, aqueous sodium hydroxide. In the present work, degradation is again the main reaction. ;-Z comparison of the proportions of reagents retosyl-DL-alanyl chloride and glycine were coupled by this method. n'ith the reagents in the propor- quired by the coupling reaction with those recortlcd tions required by the equation, the peptide was o h - by Schonheimerg is interesting. 'To prepare tosylL-alanyl-L-leucine he used tosyl-~-alanylchloride ( 1 tos.SHCHRCOC1 XH2CH2COOH + PSaOH + parts) and sodium hydroxide tos.SHCHRCOSHCH2COOSa SnCl part), Id-leucine (I .i (2.2 parts), b u t for tosyl-~~-leucylglycine hc em(1) (a! 4 . I? Beecham, Clzerni?lry % I n d ? i s l i , y , 1120 ( 1 5 5 5 ) : THIS ployed tosyl-DL-leucyl chloride (1 part), glycine (2.5 J O U R N A L , 79 32.57 (19.57); ( b ) R H. \T'iley, H. L. Davis. D . l i parts) and sodium hydroxide (O.% p a r t ) . EviGensheimer and S R. Smith, ihid , 7 4 , 936 ( I K 2 ) ; 11. H . \Vile? a n d dently in the second case he found a reduction in alI
