In 1972, cymbidine A (1) was isolated from the 80% ethanol extract of the orchidaceous plant Cymbidium goeringii as a hypotensive and diuretic principle. In those days, compound 1 was suggested to contain several amino acids and amino sugars, but further structure elucidation was difficult because of its structural complexity. Our recent investigation on cymbindine A (1) resulted in the elucidation of the whole structure. The molecular formula of cymbidine A (|α|_D^<22>-28.4°) was found to be C_<39>H_<63>N_7O_<20> by HRESIMS and ^<13>C NMR data (Table 1). Based on the amino acid analysis of the hydrolysate of 1 (Figure 2), valine (Val), glutamic acid (Glu), alanine (Ala) and an unusual amino acid were detected. The HMQC revealed the direct correlations between ^<13>C and ^1H signals (Table 1). The analysis of ^1H-^1H COSY and/or TOCSY indicated the partial structures a〜g (Figure 3) in 1. The partial structures were connected by HMBC correlations to give the plane structure of 1 (Figure 3). The absolute configurations of the three amino acid residues in 1 were determined to be L-Val, D-Glu and D-Ala by the advanced Marfey method. The unusual amino acid was found to be 2,6-diaminopimelic acid (A_2pm) whose meso stereochemistry was assigned by comparison of HPLC retention time with those of DD-, LL- and meso-A_2pm. The relative configurations of two aminosugars were elucidated by the analysis of ^1H-^1H spin coupling constants as well as NOESY spectral data (Figure 4), to exhibit that these aminosugars were N-acetylglucosamine and 1,6-anhydro-N-acetyl muramic acid.
