3-Prenyl-2-quinolone

Prenyl-quinolones and Related Tricyclic Alkaloids.—The l-methyI-3-prenyl-2-quinolone (6 R1 = H, R2 = OMe), already known as a synthetic compound, has been isolated from the roots of Glycosmis mauritiana it is converted into a mixture of the dihydropyrano-quinolones (8 R1 = H, R2 = OMe) and (9 R1 = H, R2 = OMe) by formic acid (Scheme 2).4 A new l-methyl-3-prenyl-2-quinolone, 7V-methylpreskimmianine (6 R1 = R2 = OMe), was obtained from the stem bark of Vepris louisii-, its structure was established by spectroscopy and by its preparation from preskimmianine (7) (Scheme 2).11 A second new alkaloid of Vepris louisii, named veprisine, was shown by spectroscopic studies and by its synthesis from A-methylpreskimmianine to be the pyrano-quinolone (10) (Scheme 2).11 Five furoquinoline alkaloids were found in the wood of Esenbeckia flava (see Table 1) and a non-crystalline bisprenyl compound (11) was also isolated from this source the new alkaloid, which was first obtained as a synthetic compound,17 is readily converted into the dihydropyrano-4-quinolone (9 R1 = R2 = H) (Scheme 2).1... 

Hydroxy-l-methyl-3-prenyl-2-quinolones, cf. (22), are key intermediates in the synthesis of quinoline alkaloids, and usually are prepared in one stage from an N-methyl-aniline and diethyl prenylmalonate. Interesting new methods beginning with N-methylisatoic anhydrides, cf. (20), have been explored and briefly repor-... 

Methoxy-3-prenyl-2-quinolones were first prepared in connection with the synthesis and biosynthesis of quinoline alkaloids (Volume IX, pp. 247, 257), but soon afterward prenyl derivatives were identified as constituents of rutaceous plants (Table I). -Prenyl and O-geranyl ethers without, substituents in the 3-position of the quinoline nucleus will be discussed in Section V of this chapter. 

Mitscher and co-workers (30) have explored alternative methods of synthesizing 3-prenyl-2-quinolones (Scheme 2) whereby the formation of by-products characteristic of the prenylmalonate route is avoided by blocking the 3-position. Thus, allylation of the 3-bromo-4-hydroxy-Af-methyl-2-quinolone yielded ketone 19 which, with zinc and acid, was converted into the 3-prenyl-2-quinolone (20). The ketone 22, obtained from ester 21, was transformed into the 2-quinolone (20) by heating with copper acetate in hexamethylphosphorus triamide. 

Furoquinoline alkaloids specifically labeled with 14C in the furan ring were required for biosynthetic studies (see Section VII of this chapter), and since existing routes produced low yields, Grundon and co-workers (195, 196) developed a more efficient synthesis from 4-methoxy-3-prenyl-2-quinolones 244-246. These compounds had previously been prepared from aromatic amines and substituted malonates, but direct allylation is more suitable for the preparation of labeled compounds, employing, for example, [14C]-3,3-dimethylallyl bromide. It was found that reaction of... 

Prenyl-quinolones and Related Tricyclic Alkaloids.— The 3-prenyl-2-quinolone preskimmianine (19), first obtained from Dictamnus albus, has now been recognized as a constituent of D. angustifolius. The 3-prenyl-2-quinolone... 

Prenylquinoline Alkaloids and Related Compounds.—Glycosolone (7), the first phenolic 3-prenyl-2-quinolone, has been isolated from the root-bark of Glycosmis pentaphylla The structure of this base-soluble alkaloid was apparent from i.r. absorption at 3130 (hydrogen-bonded OH) and at 1640 cm (2-quinolone carbonyl), and from the n.m.r. spectrum. Heating glycosolone with... 

The traditional procedure for the preparation of 3-prenyl-2-quinolones involves refluxing a solution of an aromatic amine and diethyl prenylmalonate in diphenyl ether. An interesting study of other products of these reactions has led to the identification of tetracyclic compounds, cf. (31), and 3,3 -methylenebis-2-quinolones, cf. (32) mechanisms for the formation of these compounds were proposed. ... 

Anthranilic acid and acetate biosynthesize the simple quinoline alkaloids, which are then prenylated with mevalonic acid at the C-3 position to 3-prenyl-2-quinolone alkaloids (e.g., pterecortine from Ptelea trifoliata and orixine from Orixa japonica). 3-Prenyl-2-quinolone alkaloids are then cyclized to dihydrofuro-or dihydropyranoquinoline alkaloids. Hydroxylation at the C-3 position of dihy-drofuroquinoline alkaloids and subsequent loss of the isopropyl side chain produce the furoquinoline alkaloids (Fig. 5.2.8) dictamnine is a skeletal alkaloid and skimmianine is the most common alkaloid. 

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