Conformational aspects of α-hydroxy carboxylic acids, the heralds of stereochemistry

Tartrate Chirality Determines Thaumatin Crystal Habit

“…Unlike l -tartrate, the conformation of meso -tartrate at each contact site is different: the two meso -tartrate molecules are essentially mirror images of each other (the C1−C2−C3−C4 torsion angle for the meso -tartrate at R171 is −79.4°, while it is 71.1° for the meso -tartrate at R82). These conformations are different from those of l - and d -tartrate, where the four carbon atoms are coplanar . The variability in the conformation of meso -tartrate is consistent with what is found in the salts of meso -tartaric acid, where the conformation of the meso -tartrate depends on the cations with which it crystallizes. − In our case, each chiral protein site selects for one of two enantiomeric conformers of the achiral meso -tartarte.…”

“…These conformations are different from those of L-and D-tartrate, where the four carbon atoms are coplanar. 40 The variability in the conformation of meso-tartrate is consistent with what is found in the salts of meso-tartaric acid, where the conformation of the meso-tartrate depends on the cations with which it crystallizes. [41][42][43] In our case, each chiral protein site selects for one of two enantiomeric conformers of the achiral meso-tartarte.…”

Semiempirical Conformational Analysis of (R,r) - Tartaric Acid, Its Dimethyl Diester, Diamide and N, N, N', N'-Tetramethyl Diamide. Ab-Initio Calculations of Some Model Compounds

“…Existing theoretical data concerning hydroxyacetic acid were derived from abinitio calculations at RHF/4-31G level and from molecular mechanics calculations [11], They are generally in line with our calculations with some exceptions. In our calculations we observe two symmetry related minima (B), whereas earlier ab-initio calculations predicted only one minimum (A).…”

“…Results of molecular mechanics and dynamics calculations preferred the T conformation for (R,R)-tartaric acid [11], Szarecka et al performed quantum-chemical calculations concerning (R,R)-tartaric acid monoamide monomethyl ester and concluded that for this compound the T rotamer predominates [12], The T conformation for (R.R)-tartanc acid and its esters was indicated by 13 C NMR data [13,14] and by Raman optical activity (ROA) studies [15,16], On the basis of CD measurements using the benzoate excitation chirality method Gawronski et al found that O,O'-dibenzoylated (R,R) tartaric acid, its ethyl mono-and di-esters were in the T conformation, whereas O,O'-dibenzoilatcd N,N,N',N'-tetramethyl diamide of (R,R)-tartaric acid was in the G -form in alcohol solution [4], These results stimulated our interest in (R,R)-tartaric acid derivatives and prompted us to study the conformations of these compounds systematically using the quantum chemical computational methods. 52 of (R,R)-tartaric acid up to RHF/6-31G//RHF/STO-3G level [10], They concluded that the T conformer with the hydrogen bonds between -OH and 0=C groups…”