Summary: C-glycopeptidomimetics are formed by the condensation of sugar unit and analogues of amino acid residue which generates a new carbon-carbon sigma bond
. In glycopeptides, this condensation occurs in side chain of amino acid but introduction of isonitrile moiety on N-terminal of amino acid mimic unit can also be a route to produce such compounds.
This double bond is formed by the overlap of the [sp.sup.2] orbitals of C and O, thus forming a sigma bond
and pi bond; this result is confirmed by the angles between Si3-C3-O1 (120.6[degrees]), Si4-C3-O1 (118.6[degrees]), and Si3-C3-Si4 (119.8[degrees]), which are close to the ideal angle of sp hybridization (120[degrees]).
This is because the crystal structure is solved using the electron density map, and the electrons of the hydrogen atom are mostly between the hydrogen and carbon atoms' nuclei in the sigma bond
. Since the location of the hydrogen atom is dependent on the electron density in X-ray crystallography, the hydrogen seems closer to the carbon than it really is (7).