The determination of the structure of unknown compounds extracted from marine organisms or other sources is one of the core activities of the NMR lab, through the research platform SmallStruct to which Mabcent-SFI has been the main client. Examples of elucidated molecules are the novel Breitfussins A-B and C-H, some Bromophenols, the synoxazolidones and others in writing.
Structure elucidation is done together with high resolution Mass Spectrometry (MS). MS is used to determine the exact mass from which the molecule formula and isotope pattern that best fits the mass is calculated. MS fragmentation of the molecule can give additional information about substructures split from the mother ion.
NMR is then used to determine the exact molecule framework, using various experiments correlating the through-bond scalar couplings and the through-space dipolar couplings.
The sensitivity limit to do a full characterization is approximately 1 mM of compound in 120 µl solvent, corresponding to 50 µg @ 400 Da and preferably at least 1 mg of a peptide < 5-10 kDa. Smaller amounts can be analyzed to some extent, which may be enough if closely related analogues are already known or if MS sequencing is sufficient.