1,8-Dihydroxy-3-methyl-6-methoxyanthraquinone (physcion) and two derivatives, 7-(trans-3-methyl-1-butenyl)-physcion (vismiaquinone) and 7-(3-methyl-2-oxobutyl)-physcion (vismiaquinone B), were isolated respectively from Vismia cayennensis and V. japurensis. Vismia cayennensis (Jacq.) Pers. [1] and V. japurensis Reich. (Guttiferae) [2] are large shrubs which occur in north-eastern South America. The latter species has recently been located also in central Brazil (Prof. Jose Badini, private information). Wood samples were found to contain respectively physcion (1a), besides sitosterol, lupeol and betulinic acid, and the two physcion derivatives 1b and 1c, besides sitosterol, friedelin and friedelan-3β-ol. The structures of 1b and 1c resulted from a comparison of their spectral data with those of physcion (1a) [3]. The ¹H NMR spectra were very similar with respect to the signals of H-5 (δ 7.38 ± 0.04), H-4 (δ 7.59 ± 0.04), H-2 (δ 7.05 ± 0.03), Me-3 (δ 2.43 ± 0.02), OMe-6 (δ 3.98 ± 0.02) and two chelated hydroxyls. The only significant differences were that the signal of H-7 (δ 6.68) in 1a, was replaced by signals assigned to a trans-3-methyl-1-butenyl group in 1b and a 3-methyl-2-oxobutyl group in 1c. All assignments and, most importantly, the fact that the C-Me group is flanked by two aromatic protons, were confirmed by double irradiation experiments. The IR spectra were consistent with the proposed structures indicating the existence in all three compounds of chelated (ν 1623 ± 2 cm⁻¹) and unchelated (ν 1666 ± 1 cm⁻¹) anthraquinone carbonyls and in 1c additionally of an α,β-conjugated ketone function (ν 1706 cm⁻¹). Physcion (1a) is a well known natural compound and has been isolated for instance from Harungana madagascariensis Poir. which also belongs to the Guttiferae family [4]. 7-(3-Methyl-1-butenyl)-physcion (1b) has been reported previously as one of the alkaline decomposition products of vismione A, a constituent of the berries of Vismia baccifera (L.) Tr. et Pl. subsp. dealbata (H.B.K.) Ewan [5]. Gonçalves and Mors [6], who isolated 1b while our work on V. japurensis was in progress and who named the compound vismiaquinone, demonstrated, however, that the product is a genuine constituent of the leaves of V. reichardtiana (O. Ktze.) Ewan. In addition to vismione A and vismiaquinone, only the flavones artocarpin, norartocarpin [7] and chaplashine [8] from Artocarpus (Moraceae) species have been reported to contain 3-methyl-1-butenyl side chains. Delle Monache et al. [5] postulated that these groups may be formed from the more usual γ,γ-dimethylallyl chains by shift of the double bond into conjugation with the aromatic nucleus. The isolation of the novel vismiaquinone B (1c) reveals a possible mechanism for this shift. Oxygenation of the β-carbon of γ,γ-dimethylallyl groups does occur in Guttiferae, as demonstrated by psorospermin (2) [9], and an analogous intermediate substituted by -CH₂.CHOR.CHMe₂ may be a common precursor to both 1b and 1c.