Deidaclin: a natural glucoside of cyclopentenone cyanhydrin

Chemical Diversity of Plant Cyanogenic Glycosides: An Overview of Reported Natural Products

Cyanogenic glycosides are an important and widespread class of plant natural products, which are however structurally less diverse than many other classes of natural products. So far, 112 naturally occurring cyanogenic glycosides have been described in the phytochemical literature. Currently, these unique compounds have been reported from more than 2500 plant species. Natural cyanogenic glycosides show variations regarding both the aglycone and the sugar part of the molecules. The predominant sugar moiety is glucose but many substitution patterns of this glucose moiety exist in nature. Regarding the aglycone moiety, four different basic classes can be distinguished, aliphatic, cyclic, aromatic, and heterocyclic aglycones. Our overview covers all cyanogenic glycosides isolated from plants and includes 33 compounds with a non-cyclic aglycone, 20 cyclopentane derivatives, 55 natural products with an aromatic aglycone, and four dihydropyridone derivatives. In the following sections, we will provide an overview about the chemical diversity known so far and mention the first source from which the respective compounds had been isolated. This review will serve as a first reference for researchers trying to find new cyanogenic glycosides and highlights some gaps in the knowledge about the exact structures of already described compounds.

Intramolecular fluorine migration via four-member cyclic transition states

Gaseous CF(3)(+) interchanges F(+) for O with simple carbonyl compounds. CF(3)(+) reacts with propionaldehyde in the gas phase to produce (CH(3))(2)CF(+) via two competing pathways. Starting with 1-(13)C-propionaldehyde, the major pathway (80%) produces (CH(3))(2)CF(+) with the carbon label in one of the methyl groups. The minor pathway (20%) produces (CH(3))(2)CF(+) with the carbon label in the central position. The relative proportions of these two pathways are measured by (19)F NMR analysis of the neutral CH(3)CF=CH(2) produced by deprotonation of (CH(3))(2)CF(+) at <10(-)(3) Torr in an electron bombardment flow (EBFlow) reactor. Formation of alkene in which carbon is directly bonded to fluorine means that (in the minor product, at least) an F(+) for O transposition occurs via adduct formation followed by 1,3-atom transfer and then isomerization of CH(3)CH(2)CHF(+) to the more stable (CH(3))(2)CF(+). Use of CF(4) as a chemical ionization (CI) reagent gas leads to CF(3)(+) adduct ions for a variety of ketones, in addition to isoelectronic transposition of F(+) for O. Metastable ion decompositions of the adduct ions yield the metathesis products. Decompositions of fluorocycloalkyl cations formed in this manner give evidence for the same kinds of rearrangements as take place in CH(3)CH(2)CHF(+). Density functional calculations confirm that F(+) for O metathesis takes place via addition of CF(3)(+) to the carbonyl oxygen followed by transposition via a four-member cyclic transition state. A computational survey of the effects of different substituents in a series of aldehydes and acyclic ketones reveals no systematic variation of the energy of the transition state as a function of thermochemistry, but the Hammond postulate does appear to be obeyed in terms of progress along the reaction coordinate. Bond lengths corresponding to the central barrier correlate with overall thermochemistry of the F(+) for O interchange, but in a sense opposite to what might have been expected: the transition state becomes more product-like as the metathesis becomes increasingly exothermic. This reversal of the naive interpretation of the Hammond postulate is accounted for by the relative positions of the potential energy wells that precede and follow the central barrier.

Biosynthesis of cyclopentenyl fatty acids. Cyclopentenylglycine, a non-proteinogenic amino acid as precursor of cyclic fatty acids in Flacourtiaceae

In seeds of Hydnocarpus anthelminthica of Flacourtiaceae, cyclopentenylglycine and cyclopentenyl fatty acids are found naturally. The non-proteinogenic amino acid may serve as precursor of cyclopentenyl fatty acids via aleprolic acid, the starter molecule for these long-chain compounds. After administration of cyclopentenyl[2-14C]glycine to maturing seeds of H. anthelminthica, labelled cyclopentenyl fatty acids were synthesized. Comparative activities were observed, when [1-14C]aleprolic acid was supplied to the seeds. Incorporation studies with [1-14C]acetate revealed that the chain-lengthening systems for straight-chain and cyclic fatty acids were still functioning in mature seeds. Endosperm and embryo of H. Anthelminthica seeds synthesized cyclopentenyl fatty acids from cyclopentenyl[2-14C]glycine, [1-14C]aleprolic acid and [1-14C]acetate. In embryonic tissue, a dilution experiment proved the following path for cyclopentenyl fatty acid biosynthesis: cyclopentenylglycine leads to aleprolic acid leads to cyclopentenyl fatty acids. The conversion of cyclopentenylglycine to aleprolic acid may occur via transamination and oxidative decarboxylation; activated aleprolic acid is then lengthened by C2-units to cyclopentenyl fatty acids.