Isolation of Bioactive Naphthoquinone Compounds
from R. nasutus KURZ. Roots Three main naphthoquinone
esters were isolated from the roots of R. nasutus KURZ.
Briefly, dried roots of R. nasutus KURZ. (1.5 kg) were ground
and extracted with methanol using a Soxhlet apparatus. The
solvents were filtered and evaporated in vacuo by a rotary
evaporator. The methanol extract was further partitioned with
the n-hexane and following with chloroform and methanol,
affording the residues of n-hexane (5.9 g), chloroform
(14.6 g) and methanol (36.7 g) extracts, respectively.
A portion of the chloroform extract (7.6 g) was chromatographed
on a silica gel column (200 g) and eluted with
chloroform and methanol in the order of increasing polarity.
Fractions of 100 ml were collected to provide 5 fractions
(A—E) and 3 middle fractions were used for further purification.
Fraction B was rechromatographed on silica gel and
eluted with n-hexane and chloroform by increasing polarity,
affording rhinacanthin-C as red oil (1.3 g). Fraction C was
then chromatographed on silica gel, eluted with chloroform :
methanol (19 : 1) and two compounds were isolated. Recrystallization
of these compounds from n-hexane afforded rhinacanthin-C
(0.69 g) and orange needles of rhinacanthin-N
(0.112 g). Fraction D was also rechromatographed on silica
gel column, eluted with ethyl acetate : methanol (4 : 1) and
two compounds were obtained; rhinacanthin-N (0.62 g) and
rhinacanthin-Q as yellow powder (0.58 g), respectively. The
identity of three active compounds was confirmed by spectroscopic
data (UV, IR, 1
H- and 13C-NMR, MS).7