July 20, 1960
3787
COMMUNICATIONS TO THE EDITOR TABLE I
7
VALUESOF OLEPISIC PROTON IN trans
AND
czs (IVITH RESPECT To -CHI A X D - C 0 2 R ) AND
TRISUBSTITUTED OLEFIXICACIDS
ESTERS“
CHa-C-H
CH3-c--H
II
II
lvans
X-C-COIR
cis
Rod-C--X
CHI-‘2-H
3.03
/I
CHI-C-H
3.82
I1 I1
CHI-C-C0zH CHI-C-H
3.28
1
HO~C-C-CHI CHo-C-H
4.03
11
CHJ-C-CO2Me CH3-C-Hb
3.00
Me02C C-CHs CH3-C-Hb
3.82
3.3
H02C-C-CzHj CHj-C-Hd
3.70
I1
CqHj-C-COzH CHa-C-Hc
11
il
11
(CHd)2CH-C-CO&Ie
HO~C-C-CH~--C--CO~H
11
CHa CH3-C-He
I!
3.2
MeO2C-CH2-C--C0~hIe
CH3-C-1%
3.95
[I
MeO~C-C-CH~-C-C02Me
It
CHz Dimethyl integerrinecate
3.21
Dimethyl senecate 3.99 Dimethyl riddellate 3.96 Dimethyl seneciphyllate 3.90 a XI1 spectra were determined on a Varian high resolution spectrometer a t 60 Mc. per second. lye are thankful to h l r . T . Van -1uken for providing the spectra of tiglic and angelic acids and their esters (run in CClr). -111 other spectra were obtained in CDC13 using tetramethplsilane as a n internal standard. X-alues are expressed in parts per million on the “7 scale” as defined by Tiers ( J . Phys. Chem., 6 2 , 1151 (1958)). The peaks due t o the single proton appeared in all case as quartets and the values are reported for the center of each quartet. XI1 the compounds studied except cu-ethylisocrotonic acid were isomerically pure. The sample of a-ethylisocrotonic acid available was a mixture of cis and trens compounds and eonsequently had quartets at 3.00 and 3.82 corresponding t o cis and trens protons. \&’e are grateful t o Professor T . A. Geissman for a gift of senecic acid and t o the -1.P. Sloan Foundation for a grant which made this investigation possible. * E. Blaise and P. Bagard, Ann. Chim., 11, 111 (1907). R . A d a m and B . L. Van Duuren, THISJOURNAL, 74, 5349 (1952). Ref. 1. e M. C. Kloetzel, ibid.,70,3571 (1948).
shift occurs in the T value of the olefinic proton on changing the substituent X from -CH3 to -CzHb to -CH(CH3)2, etc. (4) The close agreement bebetween the values of the olefinic proton in methyl tiglate, methyl isopropylcrotonate, dimethyl ethylidenesuccinate and dimethyl integerrinecate indicates that in all these cases the proton is oriented cis to the carbomethoxyl groups. Similarly, the values for methyl angelate, dimethyl senecate, dimethyl a-methylene-a’-ethylideneglutarate (obtained from riddellic acid), dimethyl riddellate, and dimethyl seneciphyllate all have the same arrangement of groups about the double bond. ( 5 ) A small shift of the 7 value of the olefin proton toward higher field side is observed in the ester of an acid.5 The sensitivity of this correlation of the cis and trans isomers is apparent by comparing the difference of the values of the ethylidenic protons in the cis-tram pair dimethyl senecate and dimethyl integerrinecate with the differences of the values of the pairs methyl angelate and methyl tiglate, and a-ethylcrotonic acid and a-ethylisocrotonic acid. Thus orientation of groups about the olefin linkage in the necic acids, assigned on the basis of ultraviolet spectra and melting points, is confirmed. The shielding values of the methyl protons also could be used4 for determining the stereochemistry of the double bond, but the single proton values are to be preferred due to their larger sensitivity to environmental changes. Between the cis and trans compounds the shift in the methyl proton ( 8 ) N. J. Leonard in ” T h e Alkaloids,” edited b y R . H . F. Ivfanske, Vol. VI, Chapter 3, Academic Press, New York, h’. Y . , 1960.
values is about 0.2 p.p.rn. whereas the shift in the olefinic proton values is about 0.8 p.p.m. There is some evidence also that n.m .r. spectroscopy provides a valuable tool for determining the compositions of mixtures of cis and trans trisubstituted olefinic acids. SOYES CHEMICAL LABORATORY USIVERSITVOF ILLISOIS URBANA, ILLINOIS RECEIVED J U N E 8, 1960
hI. D SAIR ROGER ADAMS
T H E DEPENDENCE O F T H E CONFORMATIONS OF SYNTHETIC POLYPEPTIDES ON AMINO ACID
Sir: Several years ago the a helix3 was demonstrated by X-ray diffraction in a few synthetic polypeptides4m5I6and recently has been shown to be a basic (1) T h i s is Polypeptides. X X X . F o r t h e preceding paper in this series see E . Katchalski, G. D. F a s m a n , E . Simons, E . R . Blout, F . R . S . Gurd a n d W. L. K o l t u n . Avch. Biochenz. Biofihys.. 88, 361 (1960). Alternate address lor E. R. Blout, Chemical Research Laboratory, Polaroid Corporation, Cambridge 3 9 , Massachusetts. (2) T h i s work was supported in p a r t b y U. S. Public Health Ser\.ice G r a n t A2558 and by t h e Department of t h e Army, Office of t h e Surgeon Geneial. (3) L. Pauling. R . R . Carey a n d H . R . Branson, Pvoc. .\-all. .Icad. Sci., 1;. S . , 37, 205 (1951), e t seq. (4) C. H . B a m f o r d , U’. E . H a n b y a n d F. H a p p e y , Pvoc. K o y . Soc. ( L o n d o w ) ,206A,30(1951); C . H . Bamford, L. B r o q n , A. Elliott, W. E. H a n b y and I. F . T r o t t e r , ibid., 141B,49 (1953); C. H . Bamford, L. Brown, A. Elliott, UT.E . H a n b y and I. F. T r o t t e r , S a t w e , 175, 27 (1954). ( 5 ) Ivf. F. P e r u t z , ibid.,167, 1053 ( 1 ~ 5 1 ) . (6) H . L. Yakel, A d a Cvysl., 6, 724 (1953).
37%
Yol. 52
C O L i , ? I U S I C . \ T I O N S TO T I I E E D I T O R
hfOLECCL-4R AS11 ISFRARED Polypeptide
?*ll/c"
-
SPECTRAL
TABLE I PROPERTIES O F
-I f ienna," Pergamon Press, London, 1QX4, Vol. I X , p. 8.
July 20, 1960
COMMUNICATIONS TO THE EDITOR
3789
suggestion is supported by preliminary data obtained with copolypeptides of helix-forming and @forming amino a c i d ~ . ~ ~ (14) R. K. Kulkarni, G. D . > a s m a n a n d E. R. Blout, t o be published.
THECHILDREN'S CANCER RESEARCHFOUNDATIOS A S D HARVARD MEDICAL SCHOOL BOSTON15, MASSACHUSETTS RECEIVED JUNE 27, 1960
E. I
