Constituents of Citrus depressa (Rutaceae). Characterizations of Five New Acridone Alkaloids

Five new acridone alkaloids, citracridone-I (la), citracridone-I1 (lb), cit~ressine-I (Za), citpressine-I1 (Zb), and prenylcitpressine (3) have been isolated from the root bark of C i t r u s depressa as well as a known acridone alkaloid 2.The important chinese drug "Chen-pi" has been used for treating heartache, 1 abdominal pain, diarrhea, tussis, vomiting, inappetence and as an expectorant .The peel of various large amont C i t r u s species have been used as the source of m-g in Taiwan, and one of them has been identified with the peel of 2 Citrus d e p r e s s a Hayata naturally growed in Orchid island .This time, we collected the root bark of this plant in Orchid island and studied the constituents.This report describes the isolation and the structural elucidation of five new alkaloids named citracridone-I, -11, citpressine-I, -11, and prenylcitpressine.Citracridone-I: orange plates, m.p. 2 7 5 -2 7 8 ' , C20H19N0y The UV spectrum ( kmax 209, 270, 282(sh.),340 and 400 nrn ) showed the typical absorption associated with a 9-acridone n u c l e u ~~-~, and bathochromic shifts were observed in the presence of NaOCH3 or A ~c I ~~, indicating the presence of phenolic hydroxyl groups.The presence of two one-proton singlets at 6 14.52 and 9.33 which disappeared on D20 in the PMR spectrum indicated that at least one of the OH-groups was hydrogen bonded.Other signals in the PMR spectrum of citracridone-I are shown in Table 1.Among those signals, one of two AB- type quartets at 6 6.63 and 5.61 (J=lOHz), and a six-proton singlet at 6 1.53 could be assigned to a dimethylchromen system.Observation of a long range