Allocoronamic Acid Research Articles

Biosynthesis of (−)-(1S,2R)-Allocoronamic Acyl Thioester by an FeII-Dependent Halogenase and a Cyclopropane-Forming Flavoprotein

The biosynthetic gene cluster for the kutzneride family of hexapeptidolactones includes the four-gene cassette ktzABCD postulated to generate a nonproteinogenic amino acid. Encoded by this cassette are the nonheme FeII-dependent halogenase KtzD and the acyl-CoA dehydrogenase-like flavoprotein KtzA, proposed to work in conjunction with adenylating protein KtzB and carrier protein KtzC. In the present work, we report the in vitro reconstitution of this four-protein system and identify the final product as (1S,2R)-allocoronamic acid bound in thioester linkage to KtzC. Further analysis of KtzD and KtzA support a biosynthetic pathway that involves KtzD-mediated generation of a gamma-chloroisoleucyl intermediate which is cyclized to the final product by KtzA without redox participation of the bound flavin cofactor. This work introduces a new monomer for potential incorporation into nonribosomal peptides and validates the unique strategy for its biosynthesis.

Studies On the Synthesis of Coronamic Acid, Norcoronamic Acid and Allocoronamic Acid From 2,3 -Methanohomoserine

Coronamic acid and norcoronamic acid have been prepared in racemic form in 11% and 20% overall yields, respectively, from (E)- methanohomoserine, while the (1S,2R)-isomer of the latter allows the preparation of enantiomerically pure (1S,2R)- allocoronamic acid in 37% overall yield. Care is required to avoid intramolecular cyclisation reactions during side chain manipulation.

A straightforward synthesis of both enantiomers of allo-norcoronamic acids and allo-coronamic acids, by asymmetric Strecker reaction from alkylcyclopropanone acetals

Methylcyclopropanone hemiacetal (2 S)- 3a underwent the asymmetric Strecker reaction induced by a chiral amine to provide a useful synthesis of enantiomerically pure (1 R,2 S)-(+)- allo-norcoronamic acid 1 in good yield and high enantiomeric excess. From racemic alkyl hemiacetal (±)- 3, the same methodology also constituted a useful way to prepare both (+)- 1 and (−)- 1 and (+)- allo-coronamic acid 2 and its antipode (−)- 2 with good yield and high enantiomeric excess.

Enantioselective total syntheses of cyclopropane amino acids: Natural products and protein methanologs

Abstract The syntheses of (−)-allo-coronamic acid, (−)-allo-norcoronamic acid, (−)-(Z)-2,3-methanohomoserine, (−)-(Z)-2,3-methanomethionine, and (2S,3R)-Cbz-cyclo-Asp-OMe have been achieved in 45–68% overall yields from suitable intermediates derived from homochiral aminopentenoates which were obtained, in turn, from D-glyceraldehyde. The key synthetic step involves the quantitative and highly diastereoselective cyclopropanation of such precursors. The factors dealing with the control of stereoselectivity are highlighted and the main features in side-chain functionalization to the respective target molecules are discussed.

ChemInform Abstract: A Simple Synthesis of (‐)‐(1S,2R)‐Allocoronamic Acid in Its Enantiomerically Pure Form.

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A simple synthesis of (−)-(1 S,2 R)-allocoronamic acid in its enantiomerically pure form

(−)-(1S,2R)-Allocoronamic acid was synthesized in its enantiomerically pure form by starting from the chiral azlactone derived from 1,2-O-isopropylidene-D-glyceraldehyde in an overall yield of 37 %.

Highly efficient and stereocontrolled synthetic route to enantiopure ACC derivatives: Synthesis of (+)- N-benzyloxycarbonyl-γ,δ-dehydro- allo-coronamic acid methyl ester

Highly diastereoselective cyclopropanation of a chiral α,β-dehydroamino acid derivative, obtained from D-mannitol, leads to a single isomer which has been transformed into the title compound in 65% overall yield. This product can be a useful intermediate in the synthesis of enantiopure ACC derivatives.

Inhibitory Effect of Coronamic Acid Derivatives on Senescence in Cut Carnation Flowers

(+)-(1R,2S)-Allocoronamic acid, (−)-(1S,2R)-allocoronamic acid, and their racemate showed an inhibitory effect on senesence in cut carnation flowers. This antisenescent activity was based on the inhibition of endogenous ethylene formation catalyzed by an ethylene-forming enzyme.

Enantioselective synthesis of (+)-(1R,2S)-allocoronamic acid

The asymmetric synthesis of (+)-(1R,2S)-allocoronamic acid is reported. Diazomethane addition to (Z)-N-( tert-butoxycarbonyl)ethyldehydroalanyl-L-prolin-anhydride, easily prepared from (Z)-2-phenyl-4-propylidene-5(4H)-oxazolone and L-proline, gave in high diastereomeric excess the corresponding spiropyrazoline, which was transformed, on photolysis and acid hydrolysis of the resulting spirocyclopropane, into (+)-(1R,2S)-1-amino-2-ethyl-cyclopropanecarboxylic acid.

Extraction, partial purification and characterization of 1-aminocyclopropane-1-carboxylic acid oxidase from apple fruit

Abstract ACC oxidase (ethylene-forming enzyme — EFE) was extracted, partially purified and characterized from Golden Delicious apple fruit cortical tissue. The presence of 5% ( w v ) polyvinylpolypyrrolidone (PVPP) was necessary in the extraction medium to obtain an active enzyme from apple tissue. The specific activity was 40–100 nl ethylene h−1 mg−1 protein in the crude extract; polyethylene glycol fractionation following by calcium phosphate gel adsorption resulted in ca. 10-fold purification. Enzyme activity was retained at −20°C when the enzyme was stored with 30% glycerol. Ascorbate and Fe2+ were not essential in the extraction medium for apples. Apple ACC oxidase has a Km for ACC of 6.4 μM, Km for O2 of 0.4%, and a pH optimum of 7.2 in Tris-Mes buffer and 7.6 in phosphate buffer. The enzyme was stereospecific for substrate; it converted (±)allocoronamic acid to 1-butene while (±)coronamic acid was 10-fold less effective as a substrate. The characteristics of apple ACC oxidase are consistent with those reported for the enzyme from Cucumis melo [Ververidis and John, Phytochemistry 30 (1991), p. 727] and as demonstrated in several intact tissues [Yip et al., Plant Physiol. 88 (1988), p. 553] and in isolated pea leaf vacuoles [Gyy and Kende, Planta 160 (1984) p. 281] when consideration is made of substrate availability in vivo.

Synthesis of asymmetric (E)-α-–phenyl(ethyl)cyclopropylλycines from serine by diastereoselective dibromocylopropanation

An asymmetric synthesis of (E)-α-(2-phenylcyclopropyl)glycines and also of a homolog of allocoronamic acid, namely (E)-α-(2-ethylcyclopropyl)glycine, is reported. The key step is the dibromocyclopropanation of tert-butyl (E, 4R)- or (E, 4)-2,2-dimethyl-4-(2′-phenylvinyl)- and -(2′-ethylvinyl)-3-oxazolidinecarboxylates, easily prepared from L- or D- serine. This reaction gives good diastereomeric ratios of dibromocyclopropanes. The major compounds were transfromed, in three steps, in the corresponding cyclopropylaminoacids.

Analysis and cloning of the ethylene-forming enzyme from tomato by functional expression of its mRNA in Xenopus laevis oocytes.

The last step in biosynthesis of the plant hormone ethylene, oxidation of 1-aminocyclopropane-1-carboxylic acid (ACC), is catalysed by the elusive ethylene-forming enzyme (EFE). EFE is induced by fungal elicitors in suspension-cultured tomato cells. We demonstrate that Xenopus laevis oocytes injected with RNA from elicitor-treated tomato cells gain the ability to convert ACC to ethylene. The enzyme expressed in the oocytes under the direction of plant RNA is indistinguishable from genuine plant EFE with regard to its saturation kinetics, its iron dependency and its stereospecificity to the diastereomeric ethyl derivatives of ACC, allocoronamic acid and coronamic acid. In tomato cells stimulated for different times with elicitor, the level of EFE correlates with the level of RNA directing EFE expression in oocytes. Hybridization and co-injection experiments demonstrate that the tomato RNA species directing EFE expression in oocytes are homologous to clone pTOM13 which has been shown to inhibit ethylene production in plants when expressed in antisense. Using a cDNA library from elicitor-stimulated tomato cells, we have isolated several homologues of pTOM13 and identified one of them, pHTOM5, as a clone of EFE on the basis of its functional expression in the Xenopus oocytes.

Asymmetric Synthesis via Heterocyclic Intermediates. Asymmetric Synthesis of (-)-(1S,2R)-Allocoronamic Acid

Asymmetric Synthesis via Heterocyclic Intermediates. Asymmetric Synthesis of (-)-(1S,2R)-Allocoronamic Acid

Conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene by isolated vacuoles of Pisum sativum L.

We compared the distribution of 1-aminocyclopropane-1-carboxylic acid (ACC) between the vacuole of isolated pea (Pisum sativum L.) protoplasts and the remainder of the cell and found that over 80% of the ACC was localized in the vacuole. Isolated protoplasts and vacuoles evolved ethylene. Over 80% of the ethylene production by protoplasts could be accounted for as originating from the vacuole. Ethylene synthesis by isolated vacuoles was saturated at ACC concentrations above 1 mM, and the apparent Km for the conversion of ACC to ethylene was 61 μM. Ethylene production in isolated vacuoles was inhibited by Co(2+), n-propyl-gallate, in a N2 atmosphere, and following lysis of the vacuoles. The ethylene-forming enzyme in pea vacuoles exhibited stereospecificity inasmuch as it catalyzed the conversion of (±)-allocoronamic acid to 1-butene but not that of (±)-coronamic acid. The same stereospecificity was also shown by leaf tissue. Based on competition studies with ACC and (±)-allocoronamic acid, we conclude that conversion of ACC to ethylene and (±)-allocoronamic acid to 1-butene is mediated by the same enzyme in isolated vacuoles and in intact leaf tissue. Vacuoles isolated from Vicia faba L. leaves showed essentially the same characteristics with regard to ACC-dependent ethylene synthesis as did pea vacuoles.