C.C. da Silva

Antibacterial activity of indole alkaloids from Aspidosperma ramiflorum.

We evaluated the antibacterial activities of the crude methanol extract, fractions (I-V) obtained after acid-base extraction and pure compounds from the stem bark of Aspidosperma ramiflorum. The minimum inhibitory concentration (MIC) was determined by the microdilution technique in Mueller-Hinton broth. Inoculates were prepared in this medium from 24-h broth cultures of bacteria (10(7) CFU/mL). Microtiter plates were incubated at 37 masculineC and the MICs were recorded after 24 h of incubation. Two susceptibility endpoints were recorded for each isolate. The crude methanol extract presented moderate activity against the Gram-positive bacteria B. subtilis (MIC = 250 microg/mL) and S. aureus (MIC = 500 microg/mL), and was inactive against the Gram-negative bacteria E. coli and P. aeruginosa (MIC > 1000 microg/mL). Fractions I and II were inactive against standard strains at concentrations of < or =1000 microg/mL and fraction III displayed moderate antibacterial activity against B. subtilis (MIC = 500 microg/mL) and S. aureus (MIC = 250 microg/mL). Fraction IV showed high activity against B. subtilis and S. aureus (MIC = 15.6 microg/mL) and moderate activity against E. coli and P. aeruginosa (MIC = 250 microg/mL). Fraction V presented high activity against B. subtilis (MIC = 15.6 microg/mL) and S. aureus (MIC = 31.3 microg/mL) and was inactive against Gram-negative bacteria (MIC > 1000 microg/mL). Fractions III, IV and V were then submitted to bioassay-guided fractionation by silica gel column chromatography, yielding individual purified ramiflorines A and B. Both ramiflorines showed significant activity against S. aureus (MIC = 25 microg/mL) and E. faecalis (MIC = 50 microg/mL), with EC50 of 8 and 2.5 microg/mL for ramiflorines A and B, respectively, against S. aureus. These results are promising, showing that these compounds are biologically active against Gram-positive bacteria.

A direct route to terpene isothiocyanates

Abstract An expedient entry into the preparation of isothiocyanate terpenes is presented. The method involves the addition of isothiocyanic acid prepared “in situ” to terminal double bonds.

Coumarins From Roots of Palicourea rigida

The Palicourea genus, a member of the Psychotrieae tribe, is the second largest genus in the family Rubiaceae and includes approximately 200 species of shrubs and trees that are widely distributed in South America [1] Palicourea species are rich sources of triterpenes [2], alkaloids [3, 4], iridoids [5], and coumarins [6], many of which possess interesting biological properties. The biological and chemical importance of the Palicourea genus prompted us to investigate Palicourea rigida, a shrub popularly known as “douradao”, which is widespread in Brazilian Cerrado and is used in folk medicine as an anti-inflammatory. Previously, we reported the isolation of the alkaloid indole monoterpene vallesiachotamine [7] from the leaves of Palicourea rigida. In this paper, we describe the isolation and structural identification of the coumarins scopoletin (1), obtusifoside F (2), and hymexelsin (3) from a methanolic extract of Palicourea rigida roots. The dried and milled roots (135.0 g) from P. rigida were extracted exhaustively with cold methanol. After evaporation of the solvent in a rotary evaporator (35 C), we obtained 9.13 g of crude methanolic extract concentrate. The methanolic extract (3.8 g) was subjected to partitioning with n-hexane, chloroform, ethyl acetate, and methanol. The chloroform fraction (85.1 mg) was purified in a chromatographic column with a silica gel stationary phase and a mobile phase of increasingly polar CHCl3–MeOH mixtures. The fractions eluted with a solution of 5% CHCl3–MeOH led to the isolation of compound 1 (5.1 mg). Elution with 10% CHCl3–MeOH solution resulted in the isolation of compound 2 (2.3 mg). The water–methanolic fraction (910.0 mg) was purified in a chromatographic columm with a silica gel stationary phase and a mobile phase of increasingly polar hexane–MeOH mixtures. The fractions eluted with 40% CHCl3–MeOH resulted in the isolation of compound 3 (6.3 mg). The combined use of 1D and 2D NMR with literature data allowed us to identify the coumarins 1 as scopoletin [8], 2 as obtusifoside F [9], unprecedented in the Rubiaceae family, and 3 as hymexelsin (or xeroboside) [10, 11]. Scopoletin (1). C10H8O4, yellow solid. 1H NMR (300 MHz, CDCl3, , ppm, J/Hz): 3.90 (3H, s, OCH3), 6.21 (1H, d, J = 9.6, H-3), 6.76 (1H, s, H-8), 7.10 (1H, s, H-5), 7.86 (1H, d, J = 9.6, H-4). 13C NMR (75 MHz, CDCl3, , ppm): 164.1 (C-2), 152.9 (C-7), 151.4 (C-9), 147.1 (C-6), 146.1 (C-4), 112.6 (C-10), 112.5 (C-3), 109.9 (C-5), 103.9 (C-7), 56.8 (OCH3) [8]. Obtusifoside F (2). 7-O-[6-O-(5-O-Sinapoyl-D-apiofuranosyl)-D-glucopyranosyl]-6-methoxycoumarin. Yellow oil. Positive-ion HR-EI-MS m/z 693.1980 [M + H]+, (calcd for C32H37O17, 693.2025). For 1H and 13C NMR, see Table 1. Hymexelsin (3). 7-O-[6-O-( -D-Apiofuranosyl)-D-glucopyranosyl]-6-methoxycoumarin. For 1H (300 MHz, CD3OD) and 13C NMR (75 MHz, CD3OD), see Table 1 [10, 11].

Chemical Constituents from Leaves of Luehea paniculata

The Luehea genus occurs mainly in tropical climate regions and can be found from the Bahia South until the state of Rio Grande do Sul [1]. Studies have reported that some species belonging to this genus are used as natural remedies to treat rheumatism and haemorrhage [2]. Besides the presence of flavonoids, saponins [3] and triterpenes [4] are the main chemical constituents in species of the Luehea genus. The species Luehea paniculata Mart. is popularly known in Brazil as “acoitacavalo” and used in folk medicine to treat wounds, stomach pain, uterine disorders, hepatitis, and pneumonia [5]. Recently, antifungal and antibacterial properties of the crude extract of Luehea paniculata were reported in the literature [5]. In this context, the absence of phytochemical studies of Luehea paniculata in the literature has become relevant in this study to evaluate the chemical potential of this species present in the Cerrado. The present paper reports the isolation and structural elucidation of six known metabolites from the leaves of Luehea paniculata: -amirin (1) 6 , -amirin-3-acetate (2) 6 , maslinic acid (3) 7 , lupenone (4) 8 , oleanoic acid (5) 6 , and rutin (6) 9 .