Biology Reference
In-Depth Information
see Fig. 4.2), their ability to engage in hydrophobic associations with co-
existing substances is weaker than that of
8
. This weakness was
evidenced by a lower regioselectivity of proton up-field shifts in
interactions with gramicidin S, a cyclic peptide having β-turn structures
(Fig. 4.5) (Zhang
et al.
, 2002). In the presence of
8
(PG = PGG), large
chemical shift changes of the proline and phenylalanine moieties located
at the β-turn structure were observed, indicating that selective
association takes place. In contrast, addition of the galloylated
pedunculagin, 1-
O
-galloyl-2,3,4,6-bis-(
S
)-HHDP-β-
D
-glucose (PED),
caused non-selective up-field shifts of the amino acid protons.
HO
OH
OH
HO
O
O
OH
HO
OH
O
O
O
O
O
HO
OH
1
O
HO
O
H
O
O
O
HO
O
HO
HO
OH
OH
pentagalloyl-
β
-
D
-glucose (
8
)
O
O
OH
HO
O
O
OH
HO
OH
paeoniflorin
Fig. 4.4 Hydrophobic association of paeoniflorin and pentagalloylglucose (PGG,
8
).
The chemical shift changes caused by the addition of castalagin
(CAST), a further oxidized and highly water-soluble ellagitannin, were
much smaller than those observed with galloylated pedunculagin (PED).
These results indicated that the rigid and spherical structure of castalagin
decreased the number of interactions with the peptide molecule.
However, on solvent partition between water and
n
-octanol, the
extraction of gramicidin S into the
n
-octanol layer was strongly inhibited
at pH 3-6 by the presence of sanguiin H-6 (
21
), and no inhibition was
observed at pH 1-2, indicating that ionic interactions are also important
in peptide-ellagitannin interactions (Fig. 4.6) (Zhang
et al.
, 2000).
