Francesca Faini

Bakuchiol derivatives from the leaves of Psoralea glandulosa

Four new meroterpene derivatives have been isolated in a bioassay-guided study of the methanol extract of the leaves of Psoralea glandulosa, in addition to the known compounds bakuchiol and angelicin. Structures for the new compounds are proposed on spectroscopic evidence. The results of brine shrimp (Artemia salina) and disc-choice (Spodoptera littoralis) bioassays are interpreted in terms of the structural features.

Evaluation of synergism in the feeding deterrence of some furanocoumarins on Spodoptera littoralis

The phagodepression activity of five furanocoumarins (FC), bergapten, xanthotoxin, psoralen, imperatorin, and angelicin, has been studied against larvae of Egyptian cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) using a leaf-disk choice bioassay. The dose range used was 0–10 μg/cm2 for linear furocoumarins and 0–30 μg/cm2 for angelicin, the angular furanocoumarin. Dose–feeding deterrency activity correlations were governed by various sigmoidal functions, except in the case of imperatorin and bergapten, which had dose–response curves showing irregular traces with two maxima. All five FCs induced various degrees of phagodepression in S. littoralis; at 3 μg/cm2, the relative feeding deterrence was bergapten = xanthotoxin > psoralen = imperatorin = angelicin. Structure–activity correlations indicated that a methoxy group on C-5 or C-8 enhanced the activity. Comparison of experimental feeding deterrence of binary mixtures of imperatorin with xanthotoxin, bergapten, or psoralen at various relative concentrations with the calculated additive activity of each combination indicated that a proportion of 40% or more of imperatorin may exert a greater antifeedant effect on S. littoralis than the sum of individual compounds. The effect of angelicin also was examined in combination with psoralen, both of which are present in Psoralea plants. Their mixtures yielded a clear synergistic effect in the 20–80% angelicin range (coactivity coefficient = 124–133). By contrast, the effect of angelicin on xanthotoxin was only additive. In the dose–response curves of imperatorin/bergapten combinations, synergism was found at >60% imperatorin relative concentration and 1 μg/cm2, whereas lower proportions led to antagonism. The threshold between the two opposing effects was found to depend on the total FC concentration employed. Some natural systems contain FCs in the range of synergistic proportions recorded here and, thus, may have been produced by the host to increase its defensive effect at a lower metabolic cost.

Stereospecificity of isopentenylpyrophosphate isomerase and prenyl transferase from Pinus and Citrus

Abstract Isopentenylpyrophosphate isomerases in cell-free extracts from Pinus radiata and from Citrus sinensis eliminate the C-4 pro-S proton from mevalonic acid. Prenyl transferase from Pinus forms geranyl pyrophosphate, neryl pyrophosphate, 2,6 trans, trans farnesyl pyrophosphate and 2 cis, 6 trans farnesyl pyrophosphate from mevalonic acid. The 4-pro-S proton of mevalonic acid is eliminated in the formation of both trans and of cis double-bonds. The pattern is similar for the Citrus enzyme. Isopentenyl pyrophosphate isomerase from Pinus is completely inhibited by 15 m m iodoacetamide, which does not affect prenyl transferase. The pattern is the same for the Citrus isomerase, but less clear for the transferase. Previous work has ruled out direct trans-cis isomerization of C10 or C15 prenylpyrophosphates. Alternative mechanisms are proposed for the stereospecific elimination of the 4-pro-S proton of mevalonic acid in the biosynthesis of both cis and trans prenyl pyrophosphates.

Seasonal changes in chemical composition of epicuticular waxes from the leaves of Baccharis linearis

Abstract Extracts from the epicuticular waxes of leaves from Baccharis linearis collected at the same locality at different seasons of the year were compared in terms of relative yields, chemical composition and biological activity (feeding deterrancy against Spodoptera littoralis larvae and brine shrimp lethality bioassays). Variations detected in the concentration of some of the 13 secondary metabolites isolated in this study are discussed in connection with relevant seasonal changes of incidental environmental factors such as temperature, solar radiation, water stress and presence of predatory insects.

Chemistry, toxicity and antifeedant activity of the resin of Flourensia thurifera

The resin extract from leaves and stems of Flourensia thurifera displayed high levels of activity in the brine shrimp (Artemia safina) and antifeedant disk-choice (Spodoptera littorafis) bioassays. A bioassay-guided fractionation of the extract led to the isolation of nine known aromatic compounds (1–9) including coumarins, chromenes, a benzofuran, a flavonoid and p-coumaric acid derivatives. The results of bioassays on the pure compounds are discussed.

Neo-clerodane diterpenoids and other constituents from Baccharis species

Abstract A new neo -clerodane dilactone, desoxyarticulin, and dihydrotucumanoic acid, together with other known compounds, were isolated from Baccharis pedicellata and Baccharis marginalis . The structures of the new compounds were elucidated by spectroscopic methods.

(25R)-isonuatigenin, an unusual steroidal sapogenin from Vestia lycioides

Abstract (25 R )-Isonuatigenin, a 5 -spirosten-3β,25-diol, was isolated from aerial parts of Vestia lycioides . Its structure was elucidated mainly by 1 H NMR and 13 C NMR spectroscopy. A mixture of (25 R )-nuatigenin and (25 S )-isonuatigenin was also characterized. This is the first report on the natural occurrence of the two (25 R )-isomers.

Antioxidant capacity of abietanes from Sphacele salviae

Carnosol 1 , rosmanol 2 , carnosic acid 3 and 20-deoxocarnosol 4 , the main phenolic abietanes present in aerial parts of the Chilean medicinal plant Sphacele salviae were tested for antioxidant activity of measuring the decay of the radical cation diphenyl-picrylhydrazyl (DPPH). All compounds displayed higher antioxidant levels than BHT under the same conditions and carnosic acid was more efficient than vitamin E.

Diterpenes from Haplopappus chrysanthemifolius

Three new diterpenes were isolated from the aerial part of Haplopappus chrysanthemifolius and assigned the structures 6α-hydroxy-ent-labd-8(17)-en-15-oic acid, 3β-acetoxy-ent-labd-8(17)-en-15-oic acid and 18α-acetoxylabd-8(17)-en-15-oic acid. The structures were elucidated by high field NMR spectroscopy.

Eudesmane derivatives from Flourensia thurifera: Structure and biological activity

Abstract 3β-hydroxycostic acid and a mixture of two acyl (angelate and 3-methylbutyrate) derivatives were isolated from the aerial part of Flourensia thurifera. The structures were assigned on the basis of NMR spectra and hydrolysis. The toxicity towards Artemia salina and feeding deterrency against Spodoptera littoralis of some derivatives are also briefly discussed.