Antifungal activity of methylated nordihydroguaiaretic acids present in Larrea spp.

BUTASSI, E.; SVETAZ, L.; ZACCHINO, S.

Porto Alegre

Congreso; 5 th Meeting of Pharmaceutical Sciences Graduate Program. Mercosur Meeting on Pharmaceutical Sciencies.; 2013

Introduction: A plant lignan 3?-O-methylnordihydroguaiaretic acid (3?-OMe-NDGA) 1 was isolated by bioassay-guided fractionation from Larrea nitida and showed antifungal activities against Candida spp y Cryptococcus neoformans(Cn) better than NDGA also isolated from this plant.1 No other methylated derivative was found in L. nitida. However, nine different methylated NDGA derivatives are possible, two monomethylated 1 and 2, four dimethylated (3-6) (2Me-NDGA), two trimethylated (7 and 8) (3Me-NDGA) and one tetramethylated (10) (4Me-NDGA). Of them, three of the four 2Me-NDGA have been isolated from L. tridentata although the antifungal activity was not reported. Since the purification and isolation of these lignans is very difficult due to their chromatographic similarities, we decided to synthesize the mono, di- tri- and tetramethylated NDGA, some of them found in Larrea spp. for testing them for antifungal propertiies. Objective(s): To obtain mono, di, tri and tetramethylated NDGA which are found in Larrea spp. and test them against Candida albicans y Cn by bioautographic assays. Materials and Methods: To obtain methylated NDGA with various degrees of methylation we forts treated NDGA with 0,5-4 equiv. of Na2SO4 and 3-6 equiv. de K2CO3 in acetone at 56 ºC, obtaining five diferentes mixture products (entries 1-5 in Fig, 1). Bioautography: TLC plates of Silica-gel GF 254 were seeded with each entry (80 µg) and with standard drugs (50 µg) and developed with DCM:MeOH (95:5). The medium Agar-Sabouraud (Britania; Buenos Aires, Argentina) with 0.02 % of phenol-red (Sigma-Aldrich Chem Co) (1 mL/cm2), mixtured with an inoculum of 5 x 104 UFC/ml was poured over the plates. After incubation, the plates were revealed with MTT (methylthiazoliltetrazolium chloride). Results and Discussion: NDGA, mono and dimethylated derivatives showed actvity against Ca (Fig 1) and Cn, while dimethylated were active only against Cn. Tri and tetra methylated activity did not show any antifungal activity against any strain. Based on these results, it appears that two phenolic OH could be necessary for activity since both monomethylated NDGA, and two of both dimethylated NDGA possess this structural feature. Instead, not any trimethylated or tetramethylated derivatives possess a catecol moiety Conclusions: We have succesfully synthesized four groups of methylated NDGA (mono, di, tri and tetramethylated NDGA) that are present in Larrea spp. Those that do not possess the catecol moiety did not showed any antifungal activity.