Uncommon 5‐Methoxyisoflavans from Desmodium canum

Abstract

Bioactive minor components of the hexane extract of Desmodium canum root have been assigned the new structures 2-7 of complex isoflavans. Four of them contain the 6-methyl group typical of the major isoflavanone plant constituents and were named desmodians A-C and 3Ј-hydroxydesmodian

Isoflavonoids of the Leguminosae

“…160 In addition to isoflavones 45 and 46b, root extracts of Psorothamnus arborescens var. A similar pattern of activity was demonstrated for 3,9-dihydroxycoumestan (coumestrol), which occurs together with puerariafuran (140) in root extracts of Pueraria montana var. 88 MeOH extracts of the lower bark of the 'smoke tree' Psorothamnus spinosus (published under the synonym Dalea spinosa) yielded spinosans A (138) and B (139).…”

“…According to in vitro bioassays, 140 was more inhibitory than the positive control, aminoguanidine, with IC 50 values of 0.53 and 473 mM, respectively. A similar pattern of activity was demonstrated for 3,9-dihydroxycoumestan (coumestrol), which occurs together with puerariafuran (140) in root extracts of Pueraria montana var. lobata (published using the synonym Pueraria lobata), a widely studied medicinal plant.…”

“…139 Six prenylated isoflavans (99-104) isolated as minor components of root extracts of Desmodium incanum (published under the synonym Desmodium canum) are 5-oxyisoflavans, which are much less frequently observed than 5-deoxyisoflavans. 140 However, they are not (as stated) the first 5-methoxyisoflavans to be reported, as literature sources confirm. 4,106 The unusual feature of 6-C-methylation of the A-ring in desmodians A (100), B (102), C ( 103) and 3 0 -hydroxydesmodian B (104) also occurs in desmodianones A-F, which are prenylated isoflavanones from the same species.…”

“…A growth study over 7 days (same test substance concentrations) demonstrated that these isoflavans showed better growth inhibition of Naegleria fowleri after day 4 than amphotericin B. 140 However, they are not (as stated) the first 5-methoxyisoflavans to be reported, as literature sources confirm. 139 Six prenylated isoflavans (99)(100)(101)(102)(103)(104) isolated as minor components of root extracts of Desmodium incanum (published under the synonym Desmodium canum) are 5-oxyisoflavans, which are much less frequently observed than 5-deoxyisoflavans.…”

Isoflavonoids of the Leguminosae

“…136 In terms of pterocarpans, L. cyrtobotrya yielded lespecyrtins E 1 -E 7 (171)(172)(173)(174)(175)(176)(177), lespeorin G 4 (181), and the pterocarpenes lespecyrtins F 1 (209) and F 2 (210). 178 Similarly, L. oribunda afforded lespeorins G 1 -G 12 (178)(179)(180)(181)(182)(183)(184)(185)(186)(187)(188)(189), and the pterocarpenes lespeorins H 1 (211) and H 2 (212). 136 One point of structural interest in the lespecyrtin series of pterocarpans is the rarely encountered C-7 prenylation of E 2 -E 4 (172)(173)(174), either as a free prenyl group or cyclised with 8-OH to form a pyran ring.…”