Ptelea trifoliata

The first dimeric quinoline alkaloid, pteledimerine, was isolated recently from the root bark of Ptelea trifoliata (cf. Vol. 10, p. 80). Several related compounds have now been found in the same species, and the structure of one of them, pteledimeridine (16), was elucidated mainly by means of H n.m.r. and mass spectroscopy.9 The two dimeric alkaloids are isomeric and differ only in the nature of the furoquinolone portion, which has angular annelation (2-quinolone) in pteledimeridine and linear annelation (4-quinolone) in pteledimerine. 

Ruta graveolens Ptelea trifoliata. lEgle Marmelos... 

Ptelea trifoliata has star qualities in its production of quinoline alkaloids and the work of Mitscher and Reisch and their respective collaborators published during the year has added eight new alkaloids to the long list of quinolines already identified as constituents of this species. Other notable events include the isolation of araliopsine (48), the first angular hydroxyisopropyldihydrofuroquinoline alkaloid," and the identification of two alkaloids with unique structures, perfamine (11) from a Hap-lophyllum species and melochinone (2) from a member of the Sterculiaceae. ... 

Prenylquinoline Alkaloids.—A large number of alkaloids have already been separated from Ptelea trifoliata, including the hemiterpenoids with terminal double bonds that are characteristic of this species (cf. Vols. 1—3, 5, and 6). Two groups have now continued the investigation of the tertiary bases and quaternary salts of P. trifoliata. 

Almeine (26), amorphous, and M-desmethyl-N-methylatanine (27), m.p. 162-163°C, are present in the stem bark of Almeidea guyanensis (C. Moulis et al, Phytochem., 1983, 22, 2095). Treatment of the latter compound with DDQ gives rise to N-methylflindersine (28), m.p. 84°C, which occurs in the root bark of Ptelea trifoliata (J.Reisch et al., ibid., 1975, 14, 1678), and which is also the insect antifeedant... 

In earlier reports, evidence for the structure of ptelefoline (authors code number Pt/13) (7) and related iV-methyl-2-quinolone alkaloids from Ptelea trifoliata had been presented.13 A somewhat confusing situation has arisen as a result of ascribing the same name to another alkaloid isolated from the same species which, however, possesses the structure (4) and code number Pt/22.9 The structure (4) of Pt/22 was established by spectral means importantly, the mass spectrum of (4) showed a base peak at M - 15 which was attributed to the benzopyrylium ion (8). It is to be hoped that either Pt/13 or Pt/22 will be re-named in the near future. 

Quinoline Alkaloids withont 3-Substitnents.—4-Quinolones with a long-chain alkyl group in the 2-position were obtained originally from fungi, but in recent years have been shown to be present in some higher plants. A new alkaloid, 2-(n-undecyl)-4-quinolone (5 n = 10), has now been isolated from Ptelea trifoliata and its structure established by spectral data. The roots of Ruta graveolens contain an unresolved mixture of alkylquinolones (5 n = 10—13). ... 

A further study of the constituents of Ptelea trifoliata resulted in the isolation of lunidonine (2 R = Me), previously obtained from Lunasia amara, and of the new alkaloid, N-desmethyl-lunidonine (2 R = H). ... 

Three prenylquinolones and an isopentyl derivative have been isolated from Ptelea trifoliata L. compound 24 from the aerial parts of the plant growing in Arizona (32), ptelecortine (25) and pteleoline (26) from the European species (33), and compound 27 from the root bark (34). The structures of these alkaloids were identified by spectroscopic methods and, in the case of the 6,8-dimethoxy derivative (27), by synthesis (see Scheme 4, Section III,D,3) (35). 

As a result of the reported antimicrobial action of extracts of the hop tree, Ptelea trifoliata, Mitscher et al. (54) investigated the aboveground constituents and found that the sole active agent was a new phenolic quinolinium derivative pteleatinium salt. The alkaloid was isolated as the chloride, C16H20NO4CI, and was shown to be the 8-hydroxy-Af-methyl-platydesminium salt (38) on the basis of IR, UV, NMR, and mass spectrometry and of correlation with known quinoline alkaloids. Thus, pyridine effected demethylation to the 4-quinolone 39 which, with diazomethane, was converted into (+)-balfourodine (12), while methylation of pteleatinium chloride with methyl iodide and sodium carbonate gave O-methyl-... 

The flowers of Ptelea trifoliata were shown by Reisch and co-workers... 

The 7,8-methylenedioxyhydroxyisopropyldihydrofuroquinolone alkaloid, (-)-hydroxylunine (55), was isolated from Lunasia amara (Volume IX, p. 245), and the (+) enantiomer has now been shown to be a constituent of Ptelea trifoliata (55). Mitscher et al. (54) obtained the corresponding quaternary salt, O-methylhydroxyluninium salt (56), from the stems of... 

D. Terminal Olefins and Related Alkaloids 1. Alkaloids of Ptelea trifoliata... 

Another apparent anomaly arises from the assignment of an (5) configuration (54) to (—)-0-methylhydroxyluninium salt (120) by comparison of the circular dichroism spectrum with (+)-(/ )-pteleatinium salt (102) these alkaloids cooccur in Ptelea trifoliata, and the stereochemical result implies that they are derived biosynthetically from epoxides of opposite configuration. 

The biosynthesis of isopropylfuroquinolines such as lunasine (338) and lunacrine (335) has been discussed (cf. 80), but not yet established their cooccurrence with hydroxy derivatives (cf. 333) in Lunasia amara and in Ptelea trifoliata suggests that the two groups of alkaloids are interrelated biosynthetically, for example by a pathway involving successive dehydration and reduction via terminal olefins (Scheme 29). This scheme is supported by the presence of terminal olefins in P. trifoliata but not by the stereochemistry of the alkaloids (-)-(R)-lunacrine (335) and... 

Ptelea trifoliata is the only known source of hemiterpenoid quinoline alkaloids containing terminal double bonds, and nine compounds of this type have been isolated cf. Vols. 1—3, 5, and 7) the synthesis of two members of the group, O-methylptelefolonium iodide (26) and ptelefolone (29), has now been reported (Scheme 4). The 3-prenyl-4-methoxy-2-quinolone (24) was prepared by standard procedures and was converted with a peroxy-acid into a mixture of the dihydropyrano-quinolone (25) and the dihydrofuro-quinolone (27), Treatment of the latter with thionyl chloride and pyridine resulted in regiospecific elimination to give a terminal olefin, which afforded O-methylptelefolonium iodide (26). Successive reaction of the N-methyl-4-quinolone (28) cf. Vol. 7) with triphenyl phosphite dichloride and with pyridine resulted in an efficient synthesis of ptelefolone (29). 

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