Hydrogen-bonded rotamers of 2′,4′,6′-trihydroxy-3′-formyldihydrochalcone, an intermediate in the synthesis of a dihydrochalcone from Leptospermum recurvum

Synthesis of 2′,4′,6′-trihydroxy-3′-methyldihydrochalcone, isolated as a natural product for the first time (ex Leptospermum recurvum), proceeds through 2′,4′,6′-trihydroxy-3′-formyldihydrochalcone. Two stable rotamers of this formyl derivative have been identified and the problems associated with NMR assignments of this type of compound have been attributed to conformational exchange. Rotamer ratios from molecular modelling and ab initio calculations agree well with those obtained from low temperature NMR studies. There is also excellent correlation between experimental NMR chemical shifts for the hydrogen-bonded hydroxyl protons with those derived from ab initio calculations. This formyl dihydrochalcone showed promising bioactivity in antiviral and antimicrobial assays.