The term reversed C-glycopeptidomimetics is derived for its analogy with reversed C-nucleosides, as in these reactions, instead of anomeric carbon
In previous studies, anomeric carbon
signals were generally found downfield, in the region of 95-105 ppm .
First, the covalent bond between the leaving group (L) and the anomeric carbon
atom should possess a moderate thermal stability, because the use of an unstable glycosyl donor often results in difficulty in its handling as well as low reaction yields.
Also, considering the nature of the chemistry of the PAE resin (an amino functional polymer) and that the relaxation rates of the carbonyl carbons at 173 ppm and the carbohydrate anomeric carbon
at 105 ppm are significantly increased, it is reasonable to assume that the PAE resin is interacting with these soy flour components, most likely via secondary interactions.
It is also observed that the region above 100ppm is narrower and lower than in the spectra of the other two samples, which could be due to the change at its anomeric carbon
. The intensity of the signal in the region from 80 to 82ppm, corresponding to the [C.sub.4] carbon, is higher and more conspicuous than in the native starch.
The [.sup.1]H-NMR spectrum exhibited the presence of eight olefinic protons, one methyl doublet signals, one anomeric proton signal ([[delta].sub.HI]" 5.21) confirmed by one anomeric carbon
([[delta].sub.CI"] 102.07) indicating that the compound contains one sugar moiety (Rhamnose).
Electronegative substituents at the C-2 position of saturated heterocycles or at the anomeric carbon
of a pyranose ring favor the equatorial position much less than expected; often the axial position is favored.
The glycone part was placed at C-3 of the steroidal skeleton due to HMBC interaction of H-3 (I'H 3.95) with the anomeric carbon
at I'C 101.7 (C- 1of rhamnopyranosyl).
The downfield shift ( 69.9) of C-1 depicted the sugar linkage at this carbon, which was further confirmed through HMBC spectrum (Table-5); in which oxymethylene ( 4.06 and 3.79) exhibited HMBC correlations with anomeric carbon
at 104.6 and the anomeric proton ( 4.28) correlated with C-1 ( 69.9).
The [sup.13]C NMR spectrum displayed signals of a carbonyl group at [delta] 182.10 (C-4), 14 aromatic carbons ranging 98.29-162.34, 2 anomeric carbons
at [delta] 70.67 (C-1") and 100.32 (C-1'"), 8 oxygenated carbons ranging from [delta] 68.22 to 79.9, one methyl group at [delta] 17.71 (C-6'") and one aliphatic methylene at [delta] 61.17 (C-6") (with negative phase ([down arrow]) in DEPT 135[degrees] spectrum).