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configuration. This correlation is independent of the presence or absence
of galloyl groups, the conformation of the
D
-glucopyranose core, and the
linkage positions of the biaryl component (Okuda
et al.
, 1982c). As
expected, the CD spectra of pterocaryanin C (
14
) and praecoxin B (
15
)
showed a strong positive Cotton effect near 220 nm, while compounds
12
and
13
showed a strong negative effect at the same wavelength.
Therefore, there can be no doubt concerning the absolute configuration
of the biaryl components in all four substances
12
-
15
(Fig. 5.5).
The striking similarity of the
13
C NMR spectra of the compound
pairs praecoxin B (
15
) and
13
, and pterocaryanin C (
14
) and
12
, is a
further strong indication of the identical regiochemistry of these
compound pairs (Khanbabaee and Lötzerich, 1997b, 1998). These facts
brought us to the conclusion that the postulated structures for cercidinin
A and cercidinin B should be revised. Since 1-
O
-galloyl-4,6-di-
O
-
galloyl-2,3-
O
-(
R
)-hexahydroxydiphenoyl-β-
D
-glucopyranose (
12
) and
4,6-di-
O
-galloyl-2,3-
O
-(
R
)-hexahydroxydiphenoyl-
D
-glucopyranose (
13
)
are novel compounds, we named
12
mahtabin A and
13
pariin M. On the
basis of these results, the chemical structure of cercidinin A was re-
examined and turned out to correspond to a novel ellagitannin structure
possessing an unusual 3,4-(
R
)-HHDP moiety (Tanaka
et al.
, 2001).
5.2.2 4,6-HHDP-containing ellagitannins
5.2.2.1
Total synthesis of strictinin
Strictinin (
27
) was isolated from the dried leaves of
Psidium guajava
(Okuda
et al.
, 1982e). The structure of the isolated material was
described as 1-
O
-galloyl-4,6-
O
-(
S
)-hexahydroxydiphenoyl-
β
-
D
-
glucopyranose (Nonaka
et al.
, 1984). Strictinin (
27
) was found to
possess anti-topoisomerase II activity with an IC
100
value of 500 nM
(Nonaka
et al.
, 1989c, Okuda
et al.
, 1983b), and also cytotoxic activity
against PRMI-7951 melanoma cells with an ED
50
value of 4.86 μg/ml, as
shown in an
in vitro
study involving a large number of human cancer
(Kashiwada
et al.
, 1992b).
