Plumbagin (1), droserone (2), hydroxydroserone (4) and four
new quinones, nepenthone-A, nepenth-one-B, nepenthone-C (17) and nepenthone-E
(9), have been isolated from the roots of Nepenthes rafflesiana
Jack. A fifth quinone-nepenthone-D-has been detected in the extract and has
been assigned the tentative structure (29) from its spectroscopic properties. ���
The crystal structure of nepenthone-E (9)
was determined by X-ray diffraction; diffractometer data at 295 K were refined
by full-matrix least squares to a residual of 0.061 (1040 'observed' reflections).
Crystals of nepenthone-E (9) are triclinic, Pī a
7.579 (4), b 7.764 (5), c 10.806 (7) Ǻ, α 70.86 (4), β 101.40
(5), γ 91.70 (5)°, Z 2. ���
The structure of nepenthone-C (17) has been
confirmed by an unambiguous synthesis. A synthesis of 2,7,8-trimethoxy-3-methyl-5,6-methylenedioxynaphtho-1,4-quinone
(49) has revealed that this substance (49) is not identical with the O,O-dimethyl
ether of nepenthone-A, and it is suggested that nepenthone-A is either the 5-
or 8-O-methyl ether of 2,5,8-trihydroxy-3-methyl-6,7-methylenedioxy-naphtho-1,4-quinone
[(36) or (37), respectively].