Photochemically induced electron transfer (PET) catalyzed radical cyclization: a practical method for inducing structural changes in peptides by formation of cyclic amino acid derivatives.

A new radical cyclization reaction of unsaturated amino acid derivatives is presented. The reaction is induced by photoelectron transfer (PET) catalysis and proceeds, in comparison to commonly applied methods, under mild, nonoxidizing, and nontoxic conditions in neutral medium. This type of radical cyclization reaction can be used in peptide chemistry for inducing structural changes in peptides.

Inhibition of fucosyltransferase V by a GDP-Azasugar.

A GDP-azasugar conjugate was synthesized starting from an enzymatically obtained phosphorylated azasugar. It inhibits human fucosyltransferase V at micromolar concentrations, which is discussed in terms of transition state analogy.

Ring opening-cross metathesis of unstrained cycloalkenes.

Unstrained cycloalkenes undergo ruthenium-catalysed ring opening-cross metathesis reactions with simple alpha, beta-unsaturated carbonyl compounds under mild conditions.

Ruthenium catalysed cross metathesis with fluorinated olefins.

The E-selective cross metathesis (CM) of fluorinated olefins with various functionalised alkenes in good to excellent yields is reported.

Variable and stereoselective synthesis of azasugar analogues by a ruthenium-catalyzed ring rearrangement

A novel ruthenium-catalyzed ring opening/ring closing tandem metathesis reaction with a catalytic transfer of stereocenters from a ring to an olefinic chain is described. This ring rearrangement serves as the key step in the stereoselective synthesis of the new azasugar analogues 1 and 2.

Structure-activity relationships of synthetic analogs of jasmonic acid and coronatine on induction of benzo[c]phenanthridine alkaloid accumulation in Eschscholzia californica cell cultures.

A facile test system based on the accumulation of benzo[c]phenanthridine alkaloids in Eschscholzia californica cell suspension culture (an indicator of defense gene activation) has been used to analyze a series of synthetic compounds for elicitor-like activity. Of the 200 jasmonic acid and coronatine analogs tested with this system, representative results obtained with 49 of them are presented here. The following can be summarized concerning structure-activity relationships: there is a large degree of plasticity allowed at the C-3 of jasmonic acid in the activation of defense genes. The carbonyl moiety is not strictly required, but exocyclic double bond character appears necessary. The pentenyl side chain at C-2 cannot tolerate bulky groups at the terminal carbon and still be biologically active. Substitutions to the C-1' position are tolerated if they can potentially undergo beta-oxidation. Either an alkanoic acid or methyl ester is required at C-1, or a side chain that can be shortened by beta-oxidation or by peptidase hydrolysis. Coronatine and various derivatives thereof are not as effective as jasmonic acid, and derivatives in inducing benzo[c]phenanthridine alkaloid accumulation. Jasmonic acid rather than the octadecanoic precursors is therefore considered to be a likely signal transducer of defense gene activation in planta.

The octadecanoic pathway: signal molecules for the regulation of secondary pathways.

Plant defense against microbial pathogens and herbivores relies heavily on the induction of defense proteins and low molecular weight antibiotics. The signals between perception of the aggression, gene activation, and the subsequent biosynthesis of secondary compounds are assumed to be pentacylic oxylipin derivatives. The rapid, but transient, synthesis of cis-jasmonic acid was demonstrated after insect attack on a food plant and by microbial elicitor addition to plant suspension cultures. This effect is highly specific and not caused by a number of environmental stresses such as light, heavy metals, or cold or heat shock. Elicitation of Eschscholtzia cell cultures also led to a rapid alkalinization of the growth medium prior to jasmonate formation. Inhibition of this alkalinization process by the protein kinase inhibitor staurosporine also inhibited jasmonate formation. The induction of specific enzymes in the benzo[c]phenanthridine alkaloid pathway leading to the antimicrobial sanguinarine was induced to a qualitatively and quantitatively similar extent by fungal elicitor, methyl jasmonate, and its linolenic acid-derived precursor 12-oxophytodienoic acid. It is herein proposed that a second oxylipid cascade may exist in plants starting from linoleic acid via 15,16-dihydro-12-oxophytodienoic acid to 9,10-dihydrojasmonate. Experiments with synthetic trihomojasmonate demonstrated that beta-oxidation is not a prerequisite for biological activity and that 12-oxophytodienoic acid and derivatives are most likely fully active as signal transducers. Octadecanoic acid-derived compounds are essential elements in modulating the synthesis of antibiotic compounds and are thus integral to plant defense.

Herbivore-induced volatiles: the emission of acyclic homoterpenes from leaves of Phaseolus lunatus and Zea mays can be triggered by a beta-glucosidase and jasmonic acid.

The treatment of healthy, undamaged plants of the Lima bean Phaseolus lunatus with solutions of a beta-glucosidase from bitter almonds (at 5 U.ml-1) through the petiole results in an enhanced emission of volatiles to the environment. The compounds are identical with those emitted in response to infestation with the red spotted spider mite Tetranychus urticae. Dominant products are the two acyclic homoterpenes 4,8-dimethyl-1,3E,7- dimethylnonatriene (homoterpene I) and 4,8,12-trimethyl-1,3E,7E,11-tridecatetraene (homoterpene II) which are of sesquiterpenoid and diterpenoid origin. Therefore, a beta-glucosidase of the herbivore may be considered as the true elicitor for the odor induction. Homoterpene I and most other of the herbivore-induced volatiles can also be triggered by treatment of the plant with solutions of jasmonic acid (JA) at 100 nmol.ml-1 to 10 mumol.ml-1. The C16 homoterpene II is not significantly induced by JA. The time-course of the enzymatic- and the JA-triggered induction of the volatiles is identical. The dose-response to JA parallels previous reports on alkaloid induction in cell cultures. In corn plants (Zea mays) JA triggers the emission of all volatiles which are known to be emitted in response to the damage by the beet army worm Spodoptora exigua. In summary, the emission of volatiles after damage by a herbivore resembles the production of phytoalexins in response to an attacking microorganism and uses similar elicitors and internal transduction pathways.