The quinones of nepenthes rafflesiana. the crystal structure of 2, 5-dihydroxy-3, 8-dimethoxy-7-methylnaphtho-l, 4-quinone (nepenthone-e) and a synthesis of 2, 5-dihydroxy-3-methoxy-7-methylnaphtho-1, 4-quinone (nepenthone-c)

Plumbagin (1), droserone (2), hydroxydroserone (4) and four new quiñones, 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, P1 a 7·579 (4), b 7·764 (5), c 10·806 (7) Å, α 70·86 (4), β 101·40 (5), y 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 0, 0-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].