The circular dichroism (CD) spectra of N-acetyl amino monosaccharides and some of their methoxy derivatives, N-acetyl disaccharides, the chitin series of oligosaccharides (disaccharide through hexasaccharide), and a glycopeptide linkage compound 2-acetamido-I-N-P-L-aspartyl-2-deoxy-P-D-glucopyranosylamine (GlcNAc-Asn) were measured in order to determine which structural features are influential in determining the CD in the 190-220 nm region. The CD of the (Y anomers of 2-acetamido-2-deoxy-D-glucose and -galactose (GlcNAc and GaiNAc, respectively) are identical to those of the corresponding equilibrium mixture whereas, for 2-acetamido-2-deoxy-o-mannose, the a! anomer has a significantly more positive CD in the n-w* (208-210 nm) region than does the p anomer. The CD of the o-and P-methoxy glycosides of GlcNAc and GalNAc show negative CD bands of comparable magnitude in the n-n* region (209 nm) and positive CD bands of differing magnitudes in the T-Z-* (190 nm) region. The CD spectra of p-1-4 and p-l-6 linked 2,2'-diacetamido-2,2'-dideoxyglucosyl glucoses both show a negative CD band in the n-p* region and a positive band in the QT-?r* region. The CD curves of the chitin series of oligosaccharides all exhibit a negative CD band at about 210 nm, followed by a positive band at about 192 nm. A small progressive increase in molar ellipticity per sugar residue for both the positive and negative bands with an increase in chain length is observed. The CD spectra of GlcNAc-Asn at three different pH's differ greatly from those of N-acetyl mono-and disaccharides. The CD spectrum of GlcNAc-Asn indicates a strong interaction of the exciton type between chromophores It is concluded from the CD data that the n-r* band for these compounds is not very sensitive to anomeric configuration or to disaccharide linkage of the l-4 and 1-6 types. In contrast, the CD in the n-r* region does show variation with anomeric configuration, substituent position, and linkage position. In particular, substituents at the 3 position lead to a small negative CD at 190 nm while substituents at the 4 position lead to enhanced positive CD at 190 nm.
In the past decade several papers describing ultraviolet Cotton effects of N-acetyl amino sugars have appeared. Beychok and Kabat (1) first proposed that the n-r* transition of the amide function in these com-