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A new and efficient approach to the natural sugar derivative (VI) and its α-isomer (V) is reported.

Farnesol (3a) is the precursor to the irregular C12 terpenoid (4S, 4aS, 8aS)-1,2,3,4,4a,5,8,8a-octahydro-4,8a-dimethylnaphthalen-4a-ol (= dehydrogeosmin; 1). The irregular C-backbone originates from the oxidative removal of a C3 side chain from a C15 eudesmane-type intermediate (Scheme 2). The bicyclic C-framework is assembled by a formal addition of H2O across the endocyclic double bonds of a monocyclic germacradiene-type precursor. The biosynthetic pathway follows from administration of the deuteriated farnesols 3b–e to flower heads of the cactaceae Rebutia marsoneri Werd. and mass-spectroscopic analysis of the collected volatiles.

The stereochemistry of the algal C 11 H 16 hydrocarbon giffordene 3 results from a spontaneous [1.7]-sigmatropic hydrogen shift of the thermolabile (1,3 Z ,5 Z ,8 Z )-undecatetraene 8 . An 8πe electrocyclisation of (1,3 Z ,5 Z ,-7 E )-nonatetraene 9 is substantiated for the biosynthesis of 7-methylcyclooctatriene 5 , a product of the Mediterranean brown alga Cutleria multifida . Low temperature syntheses (−30 °C) of the thermolabile precursors 8 and 9 are described. The activation energies of the [1.7]-sigmatropic hydrogen shift 8 → 3 ( E a = 67.4 kJ mol −1 ) and of the 8πe electrocyclisation 9 → 5 ( E a = 59.4 kJ mol −1 ) are the lowest values currently known for natural pericyclic reactions.

An efficient and versatile synthesis of 1-deoxy-[4,4- 2 H 2 ]- d -xylulose 1b (= 1-deoxy-[4,4- 2 H 2 ]- d - threo pentulose) from dimethyl 2,3- O -isopropylidene- d -tartrate in 31% overall yield is described. The synthetic protocol allows a flexible adaptation to other labelling patterns and isotopes. Labelled 1-deoxy-xylulose is of high value as a metabolic probe in biosynthetic studies towards terpenoids and prenylated compounds following the Rohmer pathway. © 1997 Published by Elsevier Science Ltd.

The biosyntheses of the 6-substituted cyclohepta-1,4-dienes dictyotene (1), ectocarpene (2), desmarestene (3), vinylcycloheptadiene (4) and lamoxirene (5) involve a spontaneous Cope rearrangement of thermolabile bis-alkenylcyclopropane precursors like 16, 10, 26 and 30. The unstable precursors and the rearranged cycloheptadienes were synthesised from the chiral 2-iodovinylcyclopropane 12 using Pd0 or CuI catalysed approaches. Activation parameters of the Cope rearrangements were determined. Bioassays with pre-ectocarpene 10 established the thermolabile cyclopropane (1R,2R)- 10 , rather than the cyclohepta-1,4-diene (6S)- 2 , as the genuine pheromone of the brown alga Ectocarpus siliculosus.

Stereoselective syntheses of deuterium labelled marmesins 3a-3e as metabolic probes for biosynthetic studies are described. Starting from iodo-umbelliferone (5), the title compounds were readily available by copper catalysed alkylation-cyclisation and subsequent transfer-hydrogenation of the resulting furanocoumarins 6a-6e. The bioconversion of marmesin by a microsomal preparation of A. majus yielded psoralene (4) and acetone in a single step and proceeded as a syn-elimination of the alkoxy-substituent together with a single hydrogen atom from a vicinal carbon atom (β-cleavage).

An efficient and highly diastereoselective synthesis of lamoxirene ( cis -2-cyclohepta-2,5-dienyl-3-vinyloxirane, 4 ), the gamete releasing and -attracting pheromone of the Laminariales (Phaeophyceae), is reported. Ethyl cyclohepta-2,5-diene carboxylate ( 7 ) is effectively alkylated to provide the syn -α-chlorohydrin 8 via reductive chloroallylboration with DIBAL-H and ( Z )- γ - chloroallyl - BBN . Cyclisation of the chlorohydrin 8 is readily achieved with DBU yielding the pheromone in 25% overall yield from the cyclopropyl ester 5 .

1996. The format follows the pattern of its predecessor, 1 with an emphasis on the isolation and synthesis of new members of the isoflavonoid family. Although the distribution of isoflavonoids among plants is relatively sparse they nevertheless form a large and very distinctive subclass of the flavonoid family with a wide variety of structural variations encountered in nature. Continued interest in the isolation of new isoflavonoids arises due to the diverse range of biological activities including antimicrobial, oestrogenic and insecticidal activities which they possess. The pharmacological properties of isoflavonoids have been reported, especially papers detailing the relationship between consumption of isoflavonoids and reduction in the incidence of cardiovascular disease and cancer but these will not be discussed in this report. It is interesting to note that there has been a slight decrease in the number of new isoflavones isolated during this review period. While this may be a temporary slow down in productivity, it may also indicate that new compounds are becoming harder to find. It is significant that several new isoflavonoid oligomers are now reported (Section 8), as the existence of natural isoflavonoid oligomers has only recently been confirmed. 2 These new compounds comprising of isoflavonoid units linked to other isoflavonoid and neoflavonoid units complement the rare series of isoflavonoids linked to flavonoid, stilbene and phenylpropanoid units. In addition to this report two further papers detailing isoflavonoids from African plant species 3 and the chemical and biological aspects of isoprenoid substituted isoflavonoids 4 have been published.

Oxazolidine vinyl oxirane 1, a novel and highly versatile building block for the preparation of enantiopure D-(+)-erythro-sphingosine and analogues, has been prepared by chloroallylboration of the Garner aldehyde with absolute stereocontrol and in good yield.

A practical and straightforward procedure is described for the diastereoselective synthesis of functionalized cis- and trans-vinyloxiranes. Readily available esters and lactones were sequentially treated in a one-pot procedure with DIBAL-H and (Z)-γ-chloroallyl-BBN or (E)-phenylthioallyltitanium reagents to give syn-β-chlorohydrins or anti-β-hydroxy thioethers in good yields with high regio- and diastereoselectivities. The β-hydroxy intermediates were stereoselectively converted into the corresponding cis- or trans-vinyloxiranes upon treatment with DBU (for halohydrins) or by alkylation/elimination (for β-hydroxy thioethers). The protocol tolerates several functional groups and promises to be of general applicability.

A short stereoselective synthesis of both enantiomers of N-(17-hydroxylinolenoyl)-L-glutamine (volicitin) 12, an elicitor of plant volatile biosynthesis from beet armyworm salivary secretion, is described; the protected 17-hydroxylinolenic acid 4 moiety of volicitin 12 was prepared in a one pot bis-Wittig reaction.

The asymmetric synthesis of all four stereoisomers of lamoxirene (cis-2-cyclohepta-2,5-dienyl-3-vinyloxirane), the spermatozoid-releasing and -attracting pheromone of the Laminariales (Phaeophyceae), is reported. Chiral ethyl cyclohepta-2,5-diene carboxylates, prepared by a divinylcyclopropane Cope rearrangement, were effectively alkylated by means of a novel tandem DIBAL-H reduction/asymmetric alpha-chloroallylboration using (Z)-gamma-chloroallyldiisopinocampheylboranes. The ensuing syn-alpha-chlorohydrins were transformed into the corresponding vinyloxiranes with DBU, providing all four isomers of the pheromone in good chemical and excellent optical yield (90-97% ee). Spermatozoid-release assays were conducted with the sympatrically growing species L. digitata, L. hyperborea, and L. saccharina and established (1'S,2R,3S)-1c as the most active isomer in all cases.

The absolute configuration of the hydroxylinolenoyl moiety of volicitin (17-hydroxylinolenoyl- l -glutamine) 1a/b from four lepidopteran larvae was determined by methanolysis and derivatisation of the resulting ester with (1R)-1-phenyl-ethylisocyanate 3 . The absolute configuration of the resulting (1′R)-17-(1′-phenyl-ethylcarbamoyloxy)-methyl linolenoates 4a/b followed from GLC comparison with synthetic references. Natural volicitin 1 from caterpillars of Spodoptera exigua, S. frugiperda, S. littoralis and Heliothis virescens (Noctuidae) exhibits a high ee (92–96%) and has a 17S configuration.

This review covers the research on brown algal pheromones from the first structural characterisation of an active principle in 1971 to the recent detailed insight into their biosynthesis. Development of analytical methods and bioassays that lead to the identification of a structural variety of different fatty acid-derived pheromones are reported. Special emphasis is focused on the inactivation of initially released pheromones through pericyclic reactions. The impact of pheromone-research on the defensive chemistry of brown algae and diatoms is discussed. 121 references are cited.

A novel procedure for the preparation of enantiopure 1,4-disubstituted 2-imidazolines is reported. Enantiopure β-amino alcohols are converted into N-hydroxyethylamides, which are reacted with excess thionyl chloride, or with thionyl chloride followed by phosphorus pentachloride to yield N-chloroethylimidoyl chlorides. These intermediates are treated with amines and anilines to produce N-chloroethylamidines, which are converted into imidazolines upon workup with aqueous hydroxide. The method is simple and efficient and has been used to prepare a wide variety of enantiopure imidazolines, in a modular fashion, from readily available amino alcohols.

N-(17-Acyloxy-acyl)-glutamine conjugates such as N-(17-linolenoyloxy-linolenoyl)-glutamine (6), N-(17-linolenoyloxy-linoleoyl)-glutamine (7), N-(17-linoleoyloxy-linolenoyl)-glutamine (8), and N-(17-linoleoyloxy-linoleoyl)-glutamine (9) were identified as novel surfactants in the oral secretion of several lepidopteran larvae (S. exigua, S. littoralis, S. frugiperda, and H. virescens) by LC-MS/MS and chemical degradation. Authentic reference compounds were synthesized via a dissymmetric bis-Wittig approach and confirmed the assigned structures.

Retrobiosynthetic analysis of the allergenic sesquiterpene lactone, anthecotuloide, suggested that this natural product could be formed either by head to head condensation of geranyl diphosphate with dimethylallyl diphosphate, or from farnesyl diphosphate (FPP), the accepted regular sesquiterpene precursor via the rearrangement of a germacranolide precursor. Isotopic labelling of anthecotuloide has now been achieved by feeding [1-(13)C]-glucose, [U-13C6]-glucose and [6,6-(2)H2]-glucose to aseptically grown plantlets of Anthemis cotula(family Asteraceae). Analysis of labelling patterns and absolute 13C abundances using quantitative 13C NMR spectroscopy showed that the isoprene building blocks of this sesquiterpene are formed exclusively via the MEP terpene biosynthetic pathway. This was supported by results from an experiment using [U-13C6]-glucose. A deuterium labelling experiment using [6,6-(2)H2]-glucose supported the original proposal and showed that anthecotuloide is formed from a non FPP precursor. Isotope ratio mass spectrometry suggested that there were two pathways for sesquiterpene biosynthesis in A. cotula.