Insect Antifeedant Benzofurans from Pericallis Species.

In this work, we have studied the benzofurans of Pericallis echinata (aerial parts and transformed roots), P. steetzii (aerial parts and transformed roots), P. lanata (aerial parts), and P. murrayi (aerial parts and roots). This work has permitted the isolation of the new benzofurans 10-ethoxy-11-hydroxy-10,11-dihydroeuparin (10), (-)-eupachinin A ethyl ether (12), 11,15-didehydro-eupachinin A (13), 10,12-dihydroxy-11-angelyloxy-10,11-dihydroeuparin (14), 2,4-dihydroxy-5-formyl-acetophenone (15) isolated for the first time as a natural product, 11-angelyloxy-10,11-dihydroeuparin (16), and 12-angelyloxyeuparone (17), along with several known ones (1-9, 11). In addition, the incubation of the abundant component, 6-hydroxytremetone (1), with the fungus Mucor plumbeus has been studied. Benzofurans in the tremetone series (1, 1a, 2-5, 18, 18a), the euparin series (6, 7, 7a, 8-10, 14, 16), and the eupachinin-type (11, 12) were tested for antifeedant effects against the insect Spodoptera littoralis. The antifeedant compounds (1, 4, 6, 11, 12) were further tested for postingestive effects on S. littoralis larvae. The most antifeedant compounds were among the tremetone series, with 3-ethoxy-hydroxy-tremetone (4) being the strongest antifeedant. Glucosylation of 1 by its biotransformation with Mucor plumbeus gave inactive products. Among the euparin series, the dihydroxyangelate 14 was the most active, followed by euparin (6). The eupachinin-type compounds (11, 12) were both antifeedants. Compounds 4, 11, and 12 showed antifeedant effects without postingestive toxicity to orally dosed S. littoralis larvae. Euparin (6) had postingestive toxicity that was enhanced by the synergist piperonyl butoxide.

Proposal for structural revision of several disubstituted tricycloalternarenes.

Mono- and di-substituted tricycloalternarenes form a group of meroterpenes isolated from epiphytic fungi. In this work, we have made thirteen proposals to correct erroneous structures of disubstituted tricycloalternarenes, also known as guignardones. Thus, in this group of compounds, structures of guignardones K, L3, M, W, tricycloalternarene B2, 15-hydroxy-tricycloalternarene 5 b, guignardiaene D, magnardones F-H and coibanols A-C, have been revised. Moreover, we have also explained why there are only two types of disubstituted tricycloalternarenes in nature, one with a -CH2-O- ß-bridge between C-6 and C-4 (6R,4S-configuration), and the other with a -CH2-O- α-bridge between C-4 and C-6 (4R,6S-configuration). Finally, the relative and absolute configurations of phyllostictone A and the absolute structure of phyllostictone D have been established by comparison with those of magnardones I and D, respectively.

Proposal for structural revision of several monosubstituted tricycloalternarenes.

Cycloalternarenes are a group of meroterpenes isolated from epiphytic fungi with a mono-, bi, tri- or tetracyclic skeleton. We have detected in the bibliography a series of monosubstituted tricycloalternarenes with erroneous structures. Thus, in this work we make several proposals to correct the structures of nineteen 4-hydroxy-tricycloalternarenes, TCA 6a, TCA 11a2, (2E)- and (2Z)-TCA 12a, 2H-(2E)-TCA 12a, TCAs 9a and F2, methyl nor-tricycloalternarate, TCAs K, L, S-W, X2 and tricycloalterfurenes A-C, and four 6-hydroxy-tricycloalternarenes, TCA 12b, TCA 13b, tricycloalterfurene D and TCA F3. Moreover, the graphic representation of TCA 14b and TCAs 15b-18b had been corrected. In addition, we have suggested that mono-hydroxylated tricycloalternarenes can only exist in nature substituted at the 4α- or 6ß-position (4R- or 6R-configuration), which could also be explained considering biogenetic reasons. We have also determined the C-4 and C-6 configuration of several monosubstituted tricycloalternarenes, whose planar structure had been previously determined. Thus, compounds of the "series a" such as TCAs 1a-8a, 11a and ACTG-toxin H have a 4R-configuration, whilst in the "series b" TCAs 3b-7b and TCAs 9b-11b possess a 6R-configuration.

Sesquiterpene Lactones from Artemisia absinthium. Biotransformation and Rearrangement of the Insect Antifeedant 3α-hydroxypelenolide.

Three new compounds, the sesquiterpenes absilactone and hansonlactone and the acetophenone derivative ajenjol, have been isolated from a cultivated variety of Artemisia absinthium. In addition, the major lactone isolated, 3α-hydroxypelenolide, was biotransformed by the fungus Mucor plumbeus affording the corresponding 1ß, 10α-epoxide. A cadinane derivative was formed by an acid rearrangement produced in the culture medium, but not by the enzymatic system of the fungus. Furthermore, 3α-hydroxypelenolide showed strong antifeedant effects against Leptinotarsa decemlineata and cytotoxic activity to Sf9 insect cells, while the biotransformed compounds showed antifeedant postingestive effects against Spodoptera littoralis.

Alkane-, alkene-, alkyne-γ-lactones and ryanodane diterpenes from aeroponically grown Persea indica roots.

This work presents the study of the roots of the Macaronesian paleoendemism Persea indica (L.) Spreng. The root biomass of this protected tree species has been produced by soil-less aeroponic culture under controlled environment. This system has important advantages over traditional plant production techniques because it provides opportunities to optimize the yield of metabolite production under well-controlled conditions, thereby facilitating commercial-scale production of bioactive compounds. Thus, for the first time a study of this type has permitted the isolation from the roots of seven undescribed dextrorotatory lactones: the alkane-γ-lactones (+)-majoranolide and (+)-dihydromajorenolide, the alkene-γ-lactones (+)-majorenolide and (+)-majorenolide acetate, and the alkyne-γ-lactones, (+)-majorynolide, (+)-majorynolide acetate and (+)-isomajorynolide. In addition, thirteen known compounds were also isolated including two possible avocadofurane precursors, avocadynone acetate and avocadenone acetate, the monoterpene esters cis- and trans-p-coumarate of (-)-borneol, and the ryanoid diterpenes cinnzeylanone, anhidrocinnzeylanine, cinnzeylanine, cinnzeylanol, epiryanodol, perseanol, cinncassiol E, perseaindicol and secoperseanol. The configuration at C-14 de two ryanodane diterpenes has also been revised in this work. Furthermore, (-)-borneol cis-p-coumarate has showed to be insecticidal to S. littoralis and cytotoxic to insect (Sf9) cells, (+)-majorenolide antifeedant to aphids and cytotoxic to Sf9, cinnceylanol antifeedant and insecticidal to S. littoralis, and (+)-majorynolide (2), insecticidal against S. littoralis, cytotoxic to Sf9 and nematicidal, suggesting a defensive role for these compounds.

Studies on the sesquiterpene lactones from Laurus novocanariensis lead to the clarification of the structures of 1-epi-tatridin B and its epimer tatridin B.

The germacranolide 1-epi-tatridin B has been isolated from the aerial parts of Laurus novocanariensis. We have observed that the identification of this lactone and its epimer tetradin B in the scientific literature is confusing and contradictory. We have therefore studied this issue clarifying errors and contributing to the structural elucidation of other related products. Moreover, we have isolated from this plant a lactone with an 1,5-ether bridge, previously obtained from Austrolabium candidum. We have now named it austroliolide, reassigned its 13C NMR spectrum and compared its structure with that of badgerin. In addition, we have also isolated from L. novocanariensis the known germacranolides artemorin, costunolide, tatridin A, tulirinol and verlotorin, the eudesmanolides ß-cyclopyrethrosin, 1ß-hydroxy-arbusculin A, magnoliaolide and reynosin, and the guaianolide dehydrocostus lactone.

Bioactive constituents from transformed root cultures of Nepeta teydea.

A phytochemical study of an extract from transformed root cultures of Nepeta teydea, induced by Agrobacterium rhizogenes, led to the isolation of the following new compounds: the sesquiterpene (-)-cinalbicol, the diterpene teydeadione (6,11,14-trihydroxy-12-methoxy-abieta-5,8,11,13,15-penten-7-one), a degraded C23-triterpene (teydealdehyde) and three fatty acid esters of lanosta-7,24-dien-3ß-ol. The propyl ester of rosmarinic acid was also isolated for the first time from a natural source. In addition, two dehydroabietane diterpenes, eight triterpenes and eighteen known phenolic compounds were obtained. The antifeedant, cytotoxic and phytotoxic activities of the isolated compounds have also been investigated.

The Dimerization of Precocene I.

In an earlier work we reported that treatment of precocene I with Brönsted and Lewis acids produces its oligomerization, giving dimers, trimers, tetramers, etc. Now, in this article we show that bromination of precocene I with phenyltrimethylammonium tribromide (PTT) blocks its oligomerization giving a dibromo- dimer, which was reduced with tri-n-butyl tin hydride affording the same dimer obtained in the reactions with acid, thus avoiding the oligomerization. Additionally, the oxidations of precocene I with Jones reagent afforded the corresponding 3-hydroxy-4-chromanone, 3,4-chromandione, 3,4-diacid, and two dimers.

Biotransformation of an africanane sesquiterpene by the fungus Mucor plumbeus.

Biotransformation of 8ß-hydroxy-african-4(5)-en-3-one angelate by the fungus Mucor plumbeus afforded as main products 6α,8ß-dihydroxy-african-4(5)-en-3-one 8ß-angelate and 1α,8ß-dihydroxy-african-4(5)-en-3-one 8ß-angelate, which had been obtained, together with the substrate, from transformed root cultures of Bethencourtia hermosae. This fact shows that the enzyme system involved in these hydroxylations in both organisms, the fungus and the plant, acts with the same regio- and stereospecificity. In addition another twelve derivatives were isolated in the incubation of the substrate, which were identified as the (2'R,3'R)- and (2'S,3'S)-epoxy derivatives of the substrate and of the 6α- and 1α-hydroxy alcohols, the 8ß-(2'R,3'R)- and 8ß-(2'S,3'S)-epoxyangelate of 8ß,15-dihydroxy-african-4(5)-en-3-one, the hydrolysis product of the substrate, and three isomers of 8ß-hydroxy-african-4(5)-en-3-one 2ξ,3ξ-dihydroxy-2-methylbutanoate. The insect antifeedant effects of the pure compounds were tested against chewing and sucking insect species along with their selective cytotoxicity against insect (Sf9) and mammalian (CHO) cell lines.

Bioactive compounds from transformed root cultures and aerial parts of Bethencourtia hermosae.

A chemical study of Bethencourtia hermosae, aerial parts and in vitro root cultures, transformed by Agrobacterium rhizogenes, afforded the hitherto unreported sesquiterpenes ceratopicanol angelate (1), 8ß-hydroxy-african-4(5)-en-3-one tiglate (4), 8ß-hydroxy-african-4(5)-en-3-one 3'-angeloxy-2'-methylbutanoate (5), 1α,8ß-dihydroxy-african-4(5)-en-3-one 8ß-angelate (7) and 6α,8ß-dihydroxy-african-4(5)-en-3-one 8ß-angelate (8). In addition, 8ß-hydroxy-african-4(5)-en-3-one (6) was isolated for the first time from a natural source, along with the rare sesquiterpenoid senecrassidiol (10) and two jacaranone derivatives 14 and 16. Known pyrrolizidine alkaloids, together with previously unreported hermosine (23), have also been isolated from this plant. The insect antifeedant activities of the extracts and compounds were studied together with their cytotoxic effects against insect (Sf9) and mammalian (CHO) cell lines.

Microbial transformation of the diterpene 7-epi-foliol by Fusarium fujikuroi.

The incubation of 3alpha,7alpha,18-trihydroxy-ent-kaur-16-ene (7-epi-foliol) with the fungus Fusarium fujikuroi gave 3alpha,7alpha,18-trihydroxy-ent-kaur-16-en-18-al as the sole product. The biotransformation of other 7alpha- or 7beta-hydroxy derivatives had led to the oxidation of C-19, which is a main step in the biosynthesis of gibberellins and kaurenolides. Now, the presence of the 3alpha-hydroxyl impedes that oxidation, which is directed to the adjacent C-18 hydroxymethyl forming the corresponding aldehyde.

Natural sesquiterpenoids.

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. The literature from January to December 2012 is reviewed, and 471 references are cited.

Microbiological transformation of two 15α-hydroxy-ent-kaur-9(11),16-diene derivatives by the fungus Fusarium fujikuroi.

The incubation of 15α-hydroxy-ent-kaur-9(11),16-dien-19-oic acid (15α-hydroxy-grandiflorenic acid) with the fungus Fusarium fujikuroi gave as main metabolite its 3ß,6ß-dihydroxy derivative, which by an oxidative decarboxylation afforded a 19-nor compound with a 4,18-double bond. Other substances obtained were a 3α-hydroxy-19,6α-lactone, 3ß-hydroxy-6ß,7ß-epoxy-ent-kaur-9(11),16-dien-19-oic acid and 3ß-hydroxy-6-oxo-ent-kaur-9(11),16-dien-19-oic acid. Moreover, the biotransformation of 15α,18-dihydroxy-ent-kaur-9(11),16-diene led to the isolation of the corresponding 3ß-, 6ß-, 7α- and 12ß-hydroxy derivatives. Two metabolites formed by 16ß,17-epoxidation of the last compound and of the substrate were also obtained. These results indicated that the presence of the 9,11-double bond in the substrate impedes its 7ß-hydroxylation, which is necessary for the formation of gibberellins and seco-ring B ent-kaurenoids. However, this 9,11-unsaturation does not hinder a 6,7-dehydrogenation and further 6ß,7ß-epoxidation, characteristic steps of the kaurenolide biosynthetic pathway.

Natural sesquiterpenoids.

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. The literature is reviewed, and 435 references are cited.

Biotransformation of ent-kaur-16-ene and ent-trachylobane 7ß-acetoxy derivatives by the fungus Gibberella fujikuroi (Fusarium fujikuroi).

Candol A (7ß-hydroxy-ent-kaur-16-ene) (6) is efficiently transformed by Gibberella fujikuroi into the gibberellin plant hormones. In this work, the biotransformation of its acetate by this fungus has led to the formation of 7ß-acetoxy-ent-kaur-16-en-19-oic acid (3), whose corresponding alcohol is a short-lived intermediate in the biosynthesis of gibberellins and seco-ring ent-kaurenoids in this fungus. Further biotransformation of this compound led to the hydroxylation of the 3ß-positions to give 7ß-acetoxy-3ß-hydroxy-ent-kaur-16-en-19-oic acid (14), followed by a 2ß- or 18-hydroxylation of this metabolite. The incubation of epicandicandiol 7ß-monoacetate (7ß-acetoxy-18-hydroxy-ent-kaur-16-ene) (10) produces also the 19-hydroxylation to form the 18,19 diol (20), which is oxidized to give the corresponding C-18 or C-19 acids. These results indicated that the presence of a 7ß-acetoxy group does not inhibit the fungal oxidation of C-19 in 7ß-acetoxy-ent-kaur-16-ene, but avoids the ring B contraction that leads to the gibberellins and the 6ß-hydroxylation necessary for the formation of seco-ring B ent-kaurenoids. The biotransformation of 7ß-acetoxy-ent-trachylobane (trachinol acetate) (27) only led to the formation of 7ß-acetoxy-18-hydroxy-ent-trachylobane (33).

Antifeedant activity of fatty acid esters and phytosterols from Echium wildpretii.

Crude extracts and fractions from Echium wildpretii H. Pearson ex Hook. f. subsp. wildpretii (Boraginaceae) have been tested against insect species Spodoptera littoralis, Leptinotarsa decemlineata, and the aphids Myzus persicae, Diuraphis noxia, Metopolophium dirhodum, Rhopalosiphum maidis, and Rhopalosiphum padi. The EtOH extract and the lipid and steroidal fractions of E. wildpretii exhibited significant antifeedant activities against the aphids and L. decemlineata. Two bioactive mixtures composed of fatty acid esters and n-alkanes were obtained from the lipid fraction. The bioguided fractionation of the steroidal fraction resulted in the isolation of glutinol, ß-sitosterol, (3ß,7α)-stigmast-5-ene-3,7-diol, and (3ß,7α)-7-methoxystigmast-5-en-3-ol. The latter two compounds exhibited potent antifeedant activities against L. decemlineata indicating that the presence of an O-bearing C(7) was responsible for the activities of these molecules.

The incubation of 13α,17-dihydroxystemodane with Cephalosporium aphidicola.

The biotransformation of 13α,17-dihydroxystemodane (3) with the fungus Cephalosporium aphidicola afforded 13α,17,18-trihydroxystemodane (4), 3ß,13α,17-tri-hydroxystemodane (5), 13α,17-dihydroxy-stemodan-18-oic acid (6), 3ß,11ß,13α,17-tetra-hydroxystemodane (7), 11ß,13α,17,18-tetrahydroxystemodane (8) and 3ß,13α,17,18-tetra-hydroxystemodane (9). The hydroxylation at C-18 of the substrate points to a biosynthetically-directed transformation, because aphidicolin (2) is hydroxylated at this carbon. However, the C-3(ß) and C-11(ß) hydroxylations seem to indicate a xenobiotic biotransformation.

Phytochemistry and chemotaxonomy of Sideritis species from the Mediterranean region.

The phytochemical content of the Mediterranean species of the Sideritis genus has been reviewed. The components included in this review are monoterpenes, sesquiterpenes, diterpenes, triterpenes, sterols, flavones, coumarins and phenylpropanoids. From the chemotaxonomic point of view, we have divided the species from this region into four groups. The first of this is formed by taxa containing triterpenes, but not diterpenes. A second group is constituted by species having bicyclic diterpenes of the labdane type and not diterpenes. The third group is characterized by its content in tetracyclic diterpenes of the ent-kaurene type. A fourth group is composed of plants with tetracyclic diterpenes of the ent-beyer-15-ene and/or ent-atis-13-ene class. In addition, the relations of these Mediterranean species with those of the Macaronesian region have been examined.

On the biotransformation of ent-trachylobane to ent-kaur-11-ene diterpenes.

The microbiological transformation of trachinodiol (1) by the fungus Mucor plumbeus afforded the corresponding 1α, 2α, 3α, and 17-hydroxy derivatives (2-4 and 6), respectively. 7ß,16α,18-Trihydroxy-ent-kaur-11-ene (sicanatriol) (5) was also obtained in this feeding. The biotransformation of 1 to give 5 by this fungus may occur by enzymatic abstraction of a hydrogen atom, allylic to the cyclopropane ring, and subsequent cleavage of this ring. This route is similar to that postulated by us in plants of the genus Sideritis, where ent-trachylobane and ent-kaur-11-ene diterpenes coexist. This study confirms that hydroxylation of diterpenes by M. plumbeus occurs preferably at ring A carbons.