Structure Elucidation - Natural Products Chemistry: Sources, Separations, and Structures - page 29

EXAMPLE 3.1: PARNAFUNGINS

An example of the use of combined spectroscopic techniques is nicely illustrated
with the discovery of the parnafungins. These compounds were discovered as
new microbial metabolites from a fungal species. The parnafungins are actually
a mixture of four closely related compounds—four distinct stereoisomers named
A1, A2, B1, and B2 (see Figure 3.8) .
The structure determination presents some challenges. The compounds are
unstable and form equilibrium mixtures. The parnafungins contain a xanthone ring
system (UV and NMR are more complex) and possess a rare structural feature in
nature: cyclic: N-O-CO-, an isoxazolidinone ring (Figure 3.9).

O

O

O O O

O

O O O

N

O

O

O

O

O

N

O

O O

O

FIGURE 3.8 Chemical structures of the parnafungin group of compounds. (From Parish,
S. K. et al., 2008, J Am Chem Soc 130(22):7060-7066. With permission from the American
Chemical Society.)

O

O

O

O

N

FIGURE 3.9 Isoxazolidinone ring: Key fragments of the parnafungin molecule used to
confirm the structure. (From Parish, S. K. et al., 2008, J Am Chem Soc 130(22):7060-7066.
With permission from the American Chemical Society.)