176
N. N. Win and H. Morita
O
R
2
HO
R
1
OH
HO
O
211 (kayeassamin A) R
1 = G, R
2 = 1-oxobutyl
212 (kayeassamin B) R
1 = 1-oxobutyl, R
2 = G
213 (kayeassamin C) R
1 = 2-methyl-1-oxobutyl, R
2 = G
214 (kayeassamin D) R
1 = 3-methyl-1-oxobutyl, R
2 = G
215 (kayeassamin E) R
1 = 1-oxobutyl, R
2 = isoprenyl
216 (kayeassamin F) R
1 = 2-methyl-1-oxobutyl, R
2 = isoprenyl
217 (kayeassamin G) R
1 = 3-methyl-1-oxobutyl, R
2 = isoprenyl
O
HO
O
O
O
218 (kayeassamin H)
O
HO
HO
O
O
219 (kayeassamin I)
O
O
O
O
1-oxobutyl =
2-methyl-1-oxobutyl =
3-methyl-1-oxobutyl =
isoprenyl =
G =
Fig. 44 Structures of the new coumarins 211–219 isolated from a chloroform extract of K. assamica
flowers from Myanmar
cytotoxic effects against the Col2, KB, and LNCaP cell lines (IC 50 values in the
range 3.5–13.1 μM). In contrast, compound 207 did not show any discernible activity
against any of the tested cancer cell lines (IC 50 > ~50 μM). This preliminary biological assessment suggested that the presence of a 7-hydroxy group could be important
for exhibition of cytotoxic activity by these coumarin derivatives. In addition, an antimalarial assay, using chloroquine-sensitive D6 and chloroquine-resistant W2 clones
of Plasmodium falciparum, revealed compounds 204–207 to have moderate activities, with IC 50 values in the range of 9.7–11.1 μM against the D6 clone and IC 50
values in the range 5.1–10.4 μM against the W2 clone. The comparative values for
chloroquine, which was used as a positive control, were IC 50 0.012 μM for the D6
clone and IC 50 0.13 μM for the W2 clone. Since the selectivity indices (SIs) (237)