ABSTRACT
A simple MD-based protocol is presented to accurately predict both the sequence and order of disulfide bond formation in proteins containing multiple cysteine residues. It provides a detailed description of their dynamical and structural features, which can be used to perform ensemble-averaged ECD calculations. Plant cyclotides are used as model compounds.
Subject(s)
Cyclotides/chemistry , Cysteine/chemistry , Disulfides/chemistry , Circular Dichroism , Molecular Dynamics Simulation , Thermodynamics , Violaceae/chemistryABSTRACT
A simple IR and VCD spectra-structure relationship is proposed for the determination of the relative and absolute configurations of polyhydroxylated molecules using a series of styryl-pyrones as model compounds. Spectral signatures identified for free molecules and acetonide derivatives may be used for stereochemical assignments of related molecules without the aid of quantum-chemical calculations.
ABSTRACT
Isocorilagin, the α-anomer of the ellagitannin corilagin, has been frequently reported in the literature as a constituent of various plant species. Its identification is based mainly on the smaller value for the coupling constant of its anomeric proton when compared to that of corilagin. A careful investigation of the corilagin structure in both methanol and DMSO solutions using NMR, electronic and vibrational CD, and DFT and MD calculations confirmed that isocorilagin is the result of a solvent-induced conformational transition of corilagin, rather than its diastereoisomer. Corilagin changes from B1,4 and (o)S5 conformations of the ß-glucose core in DMSO-d6 to an inverted (1)C4 conformation in methanol-d4, which accounts for NMR observables attributed to the alleged α-anomer. This misassignment reinforces the risks of relying upon a single technique for structural elucidation and stereochemical analysis of complex natural products, especially those containing saccharide moieties.
