Strobilurins from fungi are the inspiration for the creation of the β-methoxyacrylate class of agricultural fungicides However, molecular details of the biosynthesis of strobilurins have remained cryptic Here we report the sequence of genomes of two fungi that produce strobilurins and show that each contains a biosynthetic gene cluster, which encodes a highly reducing polyketide synthase with very unusual C-terminal hydrolase and methyltransferase domains Expression of stpks1 in Aspergillus oryzae leads to the production of prestrobilurin A when the fermentation is supplemented with a benzoyl coenzyme A (CoA) analogue This enables the discovery of a previously unobserved route to benzoyl CoA Reconstruction of the gene cluster in A oryzae leads to the formation of prestrobilurin A, and addition of the gene str9 encoding an FAD-dependent oxygenase leads to the key oxidative rearrangement responsible for the creation of the β-methoxyacrylate toxophore Finally, two methyltransferases are required to complete the synthesis

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Strobilurin biosynthesis in Basidiomycete fungi

Ambient synthesis of dienals via triazole-gold and amine catalysis relay.

Ten methyl 2-methoxyimino-2-{2-[(substituted benzylidene)aminooxymethyl]phenyl}acetate and 2-methoxy- imino-2-{2-[(substituted benzylidene)aminooxymethyl]phenyl}-N-methylacetamide derivatives were synthesized. Structures of the new compounds were characterized by IR, 1H NMR and GC-MS data. These compounds at 10 µg/mL were tested in vitro against five pathogenic fungi, namely, Sclerotonia, Botrytis cinerea Pers, Gibberella zeae, Rhizoctorua solani and Pyricularia oryzae. Compounds G5, G6, G7 and G8 showed potent antifungal activities against Botrytis cinerea Pers, G7 against Gibberella zeae and G7, G8 against Rhizoctorua solani, respectively.

Synthesis and Antifungal Bioactivity of Methyl 2-Methoxyimino- 2-{2-[(substituted benzylidene)aminooxymethyl]phenyl}acetate and 2-Methoxyimino-2-{2-[(substituted benzylidene)aminooxy- methyl]phenyl}-N-methylacetamide Derivatives

. TiCl4–Et3N or –Bu3N reagent conducted a highly (Z)-stereoselective carbon homologation (dehydration type Ti-Claisen condensation) of alkyl α-heteroatom (halo and sulfonyloxy)-substituted acetates (XCH2CO2R) with alkyl formates (HCO2R) to afford various alkyl β-alkoxy-α-halo or sulfonyloxy-substituted acrylates (24 examples; 51%–91% yield). Stereoretentive Suzuki-Miyaura, Negishi, and Sonogashira cross-couplings using the obtained methyl β-methoxy-α-halo or sulfonyloxy-substituted acrylates proceeded smoothly to produce a variety of β-alkoxy-α-substituted acrylates in moderate to high yield (35 examples; 29% – 99% yield). As a successful application, a 3-step straightforward synthesis of strobilurin A was performed utilizing the present reaction sequence (dehydration type Ti-Claisen condensation and Suzuki-Miyaura cross-coupling), wherein the geometry of the three consecutive olefins (2E,3Z,5E) was completely maintained.

Dehydration‐type Ti‐Claisen Condensation (Carbonhomologation) of α‐Heteroatom‐substituted Acetates with Alkyl Formates: Utilization as (Z)‐Stereodefined Cross‐coupling Partners and Application to Concise Synthesis of Strobilurin A

Known synthetic precursors of strobilurins A and X, i.e., methyl (3Z,5E)-6-aryl-3-methylhexa-3,5-dienoates (aryl is phenyl, 4-methoxyphenyl), were synthesized by highly stereospecific reactions from 2-(2-tert-butyldimethylsilyloxyethyl)- and 2-[2-(4-methoxybenzyloxy)-ethyl]-5-arylpenta-2E,4E-dien-1-ols. These dienols were efficiently dehydroxylated to (1E,3Z)-4-methyl-6-(4-methoxybenzyloxy)hexa-1,3-dienylarenes with their subsequent demethoxyben-zylation to (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols. The latter through the step of corresponding aryldienals and aryldienoic acids were transformed to the target methyl (3Z,5E)-6-aryl-3-methylhexa-3,5-dienoates, which completes a formal synthesis of strobilurins A and X. Configuration of the C=C bonds of the conjugated aryldiene system is preserved in the considered transformations by 95–97%.

Formal synthesis of strobilurins A and X

Stereoselective synthesis of key intermediates for the preparation of strobilurins

A condensation of α,β-unsaturated aldehydes with O-protected 4-hydroxybutanal N-(tert-butyl)-imine has been exemplified for the first time using (E)-cinnamic and (E)-4-methoxycinnamic aldehydes. (E,E)-2,5-Disubstituted penta-2,4-dienals, which are key intermediates in the synthesis of strobilurins A and X, were prepared in good yields and close to 100% stereoselectivity.

Highly stereoselective synthesis of 2,5-disubstituted (E, E)-penta-2,4-dienals

(2E,4E)-2-(2-Benzyloxyethyl)-5-(4-chloro-3-methoxyphenyl)penta-2,4-dienal was obtained by the condensation of 4-benzyloxybutanal N-tert-butylimine with 4-chloro-3-methoxycinnamic aldehyde with ≥98% configurational purity and 40% yield. When 4-benzyloxy-2-triethylsilylbutanal imine was used, a 7: 3 mixture of the target (2E,4E)-dienal with its (2Z,4E)-isomer was obtained in 60% yield; the latter quantitatively isomerized to the thermodynamically preferable target (2E,4E)-dienal.

Preparation of (2E,4E)-2-(2-benzyloxyethyl)-5-(3-methoxy-4-chlorophenyl)penta-2,4-dienal as a key intermediate in the synthesis of strobilurin B

(2E,4E)-5-Aryl-2-(2-benzyloxyethyl)penta-2,4-dien-1-als (aryl is phenyl and 4-methox-yphenyl) were reduced with NaBH4 quantitatively and stereospecifically to the corresponding penta-2(E),4(E)-dien-1-ols. The hydroxymethyl group in the latter was transformed into a methyl one with a stereoselectivity of 92–97%. Debenzylation of the resulting (1E,3Z)-1-aryl-6-benzyloxy-4-methylhexa-1,3-dienes with AlCl3 in the presence of PhNMe2 afforded the target (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols; the configuration of the C=C bonds in the conjugated aryl diene systems was retained at 95%.

V. A. Popovsky

Papers

Stereoselective synthesis of key intermediates for the preparation of strobilurins

Formal synthesis of strobilurins A and X

Highly stereoselective synthesis of 2,5-disubstituted (E, E)-penta-2,4-dienals

Preparation of (2E,4E)-2-(2-benzyloxyethyl)-5-(3-methoxy-4-chlorophenyl)penta-2,4-dienal as a key intermediate in the synthesis of strobilurin B

Stereocontrolled synthesis of (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols, intermediates in the synthesis of strobilurin antibiotics