Biology Reference
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supported by the fact that these four substances invariably co-exist in
their fagaceous plant sources. The initiation step of the conversion of
acutissimins into mongolicains would be the dehydrogenation of the
pyrogallol motif of the NHTP C-1-linked galloyl unit into an α-hydroxy-
ortho
-quinone/cyclohexenetrione system (see Section 4.3.5 in Chapter 4
and Section 9.3.4 below).
HO
HO
HO
OH
OH
HO
HO
O
O
HO
O
OH
O
O
HO
HO
HO
OH
OH
O
HO
O
OH
O
O
O
HO
O
O
O
O
HO
O
HO
O
HO
O
O
HO
OH
HO
OH
OH
HO
O
O
HO
O
O
O
HO
O
O
18
: mongolicain A
O
19
: mongolicain B
HO
OH
HO
OH
HO
Fig. 9.5 Examples of flavano-ellagitannins featuring a
spiro
-linked dihydrofuran-
cyclopentenone motif.
HO
The structures of other examples of analogous flavano-ellagitannins
putatively also derived from 2,3,5-NHTP- as well as 2,3-HHBP-bearing
precursors are displayed in Section 1.3.3 of Chapter 1, Section 2.1.5 of
Chapter 2 and Section 4.3.5 of Chapter 4,
e.g.
, psidinins A and B,
guavins A and C, camelliatannin F, malabathrin E, and psiguavin.
9.1.2 Biogenetic construction - What's known !?
The biosynthetic steps leading to glucopyranosic ellagitannins from their
gallotannin precursor, β-pentagalloylglucopyranose (β-PGG), are just
today starting to get elucidated, essentially thanks to the work initiated
by Gross and co-workers several years ago (see Chapter 3). A β-
