X-Ray Crystal Structure of Phyllostin, a Metabolite Produced by Phyllosticta cirsii, a Potential Mycoherbicide of Cirsium arvense

Abstract

The X-ray crystal structure of phyllostin (8-hydroxy-3-methyl-2-oxo-2,3,4a,5,8,8a-hexahydro-benzo[1,4]dioxine-6-carboxylic acid methyl ester) is reported. Phyllostin was recently and for the first time isolated, together with phytotoxin phyllostoxin and the phyllostictines A–D, from the culture filtrates of Phyllosticta cirsii, a fungal pathogen isolated from diseased Cirsium arvense leaves and evaluated as biocontrol agent of this noxious perennial weed. Phyllostin crystallizes in the monoclinic space group P21 with unit cell parameters: a = 8.371(2), b = 7.026(1), c = 9.918(1) Å, β = 92.013(8)°, Z = 2. The final refinement converged to R1 = 0.0530 for 1026 observed reflections having I > 2σ(I). In the molecule two trans joined six-membered rings are present. The cyclohexene ring adopts a half-chair conformation. The 2-oxo-1,4-dioxan ring adopts a distorted half-chair conformation. The relative stereochemistry of the four chiral centers turns out to be 3R,4aS,8R,8aS. In the crystal packing molecules form infinite chains through O–H···O intermolecular hydrogen bonds. Chains run along the crystallographic a axis forming layers of molecules stacking in the [0 1 0] direction. Graphical Abstract The X-ray crystal structure of phyllostin (8-hydroxy-3-methyl-2-oxo-2,3,4a,5,8,8a-hexahydro-benzo[1,4]dioxine-6-carboxylic acid methyl ester) (I) is reported. In the molecule two trans joined six-membered rings are present. The relative stereochemistry of the four chiral centers turns out to be 3R,4aS,8R,8aS

Fungal phytotoxins with potential herbicidal activity: chemical and biological characterization

“…67 35 was further studied to develop a rapid analytical method to estimate its content in culture preparations and to assess the phytotoxic effect for potential weed control on tobacco protoplasts by ow cytometric analysis, and on C. arvense L. protoplasts, by uorescence microscopy. 71 The 3S,4aR,8S,8aR absolute conguration was assigned to naturally occurring (À)-40 by computational analysis of its optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectra, while the 4aR,8S,8aR absolute conguration was assigned to (À)-scytolide only by ECD and VCD, because in this case ORD analysis turned out to be unsuitable for absolute conguration assignment. 4, Table S1 ESI †), characterized as a new pentasubstituted bicyclo-octatrienylacetic acid ester and a new pentasubstituted hexahydrobenzodioxine carboxylic acid methyl ester, respectively.…”

“…When the fungus was grown on host cheatgrass (B. tectorum) seeds, cytochalasins A, B, F and Z3 (5-7,11), as well as deoxaphomin (12) and pyrenophoric acid (71) were reisolated together with two new phytotoxic sesquiterpenoid acids, named pyrenophoric acid B and C, and the well known abscisic acid (72-74, Fig. 8, Table S1 ESI †).…”

Relationships between the stereochemistry and biological activity of fungal phytotoxins

“…The packing is also stabilized, between layers, by weak CÀ ÀHÁÁÁO interactions involving O5 carbonyl oxygen atom as acceptor. 197 Phytotoxins from Alternaria sonchi Two pure phytotoxic metabolites, called alternethanoxins A and B (59 and 62, Fig. 19), were isolated from the organic extract obtained from the solid culture of A. sonchi.…”

“…The crystal packing is characterized by strong intermolecular head to tail OÀ ÀHÁÁÁO hydrogen bonds involving the hydroxy H atom and carbonyl oxygen atom of methyl ester group. 197 Chains are packed together to form parallel layers of molecules. The packing is also stabilized, between layers, by weak CÀ ÀHÁÁÁO interactions involving O5 carbonyl oxygen atom as acceptor.…”

“…The packing is also stabilized, between layers, by weak CÀ ÀHÁÁÁO interactions involving O5 carbonyl oxygen atom as acceptor. 197…”