José S. Calderón

Tyrosinase Inhibitors from Galls of Rhus javanica Leaves and Their Effects on Insects

Abstract As a defense mechanism of the leaves of Rhus javanica (Anacardiaceae) against the aphid Melaphis chinensis (Aphididae) attack, tannic acid is rapidly accumulated and forms galls along the midrib of the leaves resulting in a unique natural medicine Gallae Rhois. Tannic acid was found to inhibit the oxidation of ʟ-3,4-dihydroxyphenylalanine (ʟ-DOPA) catalyzed by tyrosinase (EC 1.14.18.1) with an IC50 of 22 μᴍ. The aphid would detoxify the ingested toxic tannic acid to relatively nontoxic gallic acid, whereas the non-adapted pink bollworm Pectinophora gossypiella larvae are sensitive to the ingested tannic acid.

Acetylcholinesterase and Insect Growth Inhibitory Activities of Gutierrezia microcephala on Fall Army worm Spodoptera frugiperda J. E. Smith

From the aerial parts of Gutierrezia microcephala (Asteraceae), four oxyflavones were isolated, namely 5,7,2′-trihydroxy-3,6,8,4′,5′-pentamethoxyflavone (1); 5,7,4′-trihydroxy-3,6,8-trimethoxyflavone (2); 5,7,2′,4′-tetrahydroxy-3,6,8,5′-tetramethoxyflavone (3); 5,2′-dihydroxy- 3,6,7,8,4′,5′-hexamethoxyflavone (4), and an ent-clerodane, bacchabolivic acid (5). Compounds 1-5, the synthetic methyl ester (6 ), n-hexane and MeOH extracts were evaluated against the fall armyworm (Spodoptera frugiperda). Gedunin, a known insect growth regulator isolated from Cedrela spp. was used as a positive control. When tested for activity on neonate larvae into the no-choice artificial diet bioassay, flavone (1), clerodane (5), its methyl ester (6), MeOH and n-hexane extracts caused significant larval mortality with MC50 of 3.9, 10.7, 3.46. 7.95 and 7.5 ppm at 7 days, respectively, as well as growth reduction. They also increased the development time of surviving larvae and a significant delay in time to pupation and adult emergence. Acute toxicity against adults of S. frugiperda was also found, 5, 6 , gedunin and n-hexane extract had the most potent activity with LD50 value of 6.59, 15.05, 10.78, and 12.79 ppm, respectively. In addition, MeOH, n-hexane extracts, 5, 6 and gedunin caused acetylcholinesterase inhibition with 93.7,100,90.2,62.0 and 100% at 50.0 ppm, respectively; whereas 1-4 exhibited only moderate inhibitory activity. Compounds 1,5 and 6 showed inhibitory activities comparable with gedunin. These compounds could be responsible of the insect growth inhibitory activity of this plant.

Tyrosinase inhibition kinetics of anisic acid.

Abstract Anisic acid (p-methoxybenzoic acid) was characterized as a tyrosinase inhibitor from aniseed, a common food spice. It inhibited the oxidation of l-3,4-dihydroxyphenylalanine (ʟ- DOPA) catalyzed by tyrosinase with an IC50 of 0.60 mᴍ. The inhibition of tyrosinase by anisic acid is a reversible reaction with residual enzyme activity. This phenolic acid was found to be a classical noncompetitive inhibitor and the inhibition constant KI was obtained as 0.603 mᴍ. Anisic acid also inhibited the hydroxylation of ʟ-tyrosine catalyzed by tyrosinase. The lag phase caused by the monophenolase activity was lengthened and the steady-state activity of the enzyme was decreased by anisic acid.

Prenylflavans from Tephrosia watsoniana

Abstract The aerial parts of tephrosia watsoniana afforded five new flavonoids named tephrowatsin A, B, C, D and E. Their structures and stereochemistries were established by spectroscopic methods and chemical transformations.

Insect growth regulatory activity of some extracts and compounds from Parthenium argentatum on fall armyworm Spodoptera frugiperda.

Abstract Argentatins, Insect Growth Regulators, Acetylcholinesterase The methanolic extract from aerial parts of Parthenium argentatum, afforded argentatin A and B. These compounds were evaluated for their effect on the fall armyworm (Spodoptera frugiperda). Toosendanin, a commercial insecticide derived from Melia azedarach was used as positive control. When tested for activity, using neonate larvae into the no-choice artificial diet bioassays, argentatin A, argentatin B and methanol extract caused significant growth inhibitory activity with GC50 of 17.8, 36.1 and 6.4 ppm at 7 days, respectively, and increased the development time of surviving larvae in a concentration-dependent manner with RGI values of 0.40, 0.60 and 0.26, at 25.0, 25.0 and 5.0 ppm. respectively. In addition, it was possible to observe in most of the treated groups a significant delay in the time of pupation, adult emergence and deformities. Acute toxicity against adults of S. frugiperda was also found, MeOH extract had the most potent activity with LD50 value of 3.10 ppm. In addition, MeOH extract and argentatin A caused acetylcholinesterase inhibition of 93.7% and 90.0%, at 5.0 and 50.0 ppm, respectively; whereas argentatin B had only slight inhibitory activity. Therefore, the MeOH extract was identified as insecticidal extract from P. argentatum with activity at concentrations above 15.0 ppm.

The crystal structure of 6-epi-desacetyllaurenobiolide, a germacra-1(10),4-diene-12,8α-olide from Montanoa grandiflora ☆

Abstract A chloroform extract of Montanoa grandiflora afforded a novel 6β-hydroxy-germacradien-8,12-olide. Its structure was shown to be 6- epi -desacetyllaurenobiolide by spectral studies, chemical transformations and single crystal X-ray diffraction. The X-ray data demonstrate that the ten-membered ring exists in the crystal in the highly unusual [ 15 D 5 , 1 D 14 ] conformation, in which the methyl group at C-4 is α-oriented and the methyl group at C-10 is β-oriented. The two double bonds are approximately parallel rather than crossed.

Viridiflorin, an isoflavone from Tephrosia viridiflora

Abstract A new isoflavone, viridiflorin, has been isolated from Tephrosia viridiflora . Its structure was established as 4′,5,7-trihydroxy-2′,5′-dimethoxy-6-prenylisoflavone based on spectral evidence and chemical transformation.

Trypanocidal Activity of Oleoresin and Terpenoids Isolated from Pinus oocarpa

Abstract Fractionation with n-hexane/ethyl acetate (1:1 v/v) by open column chromatography of the oleoresin from Pinus oocarpa Schiede yielded two diterpenes, pimaric acid (1) and dehydroabietic acid (5), the sesquiterpene longifolene (3) and a diterpenic mixture containing pimaric acid (1), isopimaric acid (4) and dehydroabietic acid (5). Subsequently, the isolated compounds, the mixture of 1, 4 and 5, the oleoresin and the dehydroabietic acid methyl ester (2), were tested in vitro against epimastigotes of Trypanosoma cruzi, the causative agent of Chagas disease. The most active compounds were 1, 3 and the oleoresin, being as active as nifurtimox, a drug effective in the treatment of acute infection by American trypanosomiasis and used in this work as positive control.

Prenylflavanols from Tephrosia quercetorum

Abstract The roots of Tephrosia quercetorum afforded three new flavonoids named quercetols A, B and C. Their structures were established by spectroscopic methods, mainly 1 H NMR.

Labdane diterpenes from Brickellia glomerata

Abstract The leaves of B. glomerata afforded three new labdane diterpenes. Their structures and stereochemistry were established by spectroscopic methods and chemical transformations.