Extractives from Guttiferae. Part XXIII. An unambiguous synthesis of 6-deoxyjacareubin and related 3,3- and 1,1-dimethylallyl and annulated xanthones

Abstract

Unambiguous syntheses are described of 6-deoxyjacareubin (1 ) and ether derivatives of the related metabolite 1,3,5-trihydroxy-2-(3-methylbut-2-enyl)xanthone (4). In addition, related pyrano-, furo-and (3.3-, hnd 1,1dimethylallyl) -xanthones derived from 1,3,5-and 1,3,7-trihydroxyxanthone have been prepared. The nuclear Overhauser effect can differentiate a linear pyranoxanthone from its angular isomer.

Alkaloids from Oriciopsis glaberrima Engl. (Rutaceae)☆

“…The presence of an acridone skeleton was also confirmed by the EI MS mass spectrum, which showed a peak at m/z 311 (C 18 H 16 NO 4 ). Furthermore, the 1 H NMR spectrum showed signals corresponding ortho-coupled aromatic protons at d 7.13 and 6.50 (d, J = 8.8 Hz, 1H each), an aromatic proton singlet at d 6.28 (s, 1H) and a dimethylchroman ring [d 1.14 (s, 6H), 1.48 (m, 2H), 2.54 (m, 2H)] indicating the presence of a dihydro-6-desoxyjacareulin skeleton (Locksley et al, 1971). The latter was confirmed by 13 C NMR, DEPT, and 2D NMR techniques (HMBC, HSQC and COSY).…”

Psorospermin, A New Antileukemic Xanthone From Psorospermum febrifugum

“…The relative positions of the methoxyl and the dihydrofuran ring were determined from studies of the nuclear Overhauser effect (NOE). NOE has been used to distinguish linear and angular pyranoxanthones (7). In the latter case, irradiation of the C-l methoxyl causes a 31% enhancement in the singlet assigned to the C-2 proton; while in the former case only a 10%.…”

“…Boron trichloride is known to selectively demethylate methoxyl groups which are ortho to a carbonyl function (9). A C-l methoxyl of a xanthone meets this requirement, and demethylation proceeds readily, leaving other methoxyl groups untouched (7,9). The reaction of 2 with boron trichloride proceeded smoothly to give a product, 5, which was shown by high resolution mass spectrometry and elemental analysis to be monodemethylated.…”

Two Antifungal Xanthones from the Heartwood of Calophyllum Symingtonianum

“…These two xanthones 1 and 2 were isolated for the first time from C. symingtonianum, although 1 and 2 had been isolated from the wood of C. cuneifolium 6 and the heartwood of C. scriblitifolium 8 , respectively. Compound 1 can be considered the putative biogenetic precursor of compound 2 14 . As for other biological activity, compound 2 was reported to show high trypanocidal activity against epimastigotes of Trypanosoma cruzi 1 .…”