Summary
The host-selective phytotoxin victorin, produced by the fungusCochliobolus victoriae, was found to be at least partially peptidic in nature, and did not contain victoxinine. The exact mass of the M-H ion was measured by FABMS as 795.1877. Derivatives of three major acid hydrolysis products were isolated. The structures of the corresponding amino acids were assigned as 2S,3R-3-hydroxyleucine, 5,5-dichloroleucine, and 3-hydroxylysine. A into victorin by the fungus in vivo.
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All gas chromatography employed a Varian model 2100 instrument equipped with a flame-ionization detector and a 1/8 inch ID X 6 foot glass column packed with 3% OV-1 on 100/120 Gas-chrom Q. Analytical runs were temperature-programmed from 60 to 260°C at 10°C/min using a carrier gas (N2) flow rat of 30 ml/min. Retention times (min):erythro-3-hydroxyleucine TFAn-butyl ester, 6.7; TFA methyl ester, 5.1;5,5-dichloroleucine TFAn-butyl ester, 10.1; TFA methyl ester, 8.6; 3-hydroxylysine TFAn-butyl ester, 11.6; TFA methyl ester, 10.1. Semipreparative work was performed under the same conditions using a 10:1 flow splitter and a carrier flow rate of 40 ml/min.
NMR data were recorded on a Bruker WM-300 FTNMR instrument. Chemicalshifts are reported in ppm downfield from TMS. 3-Hydroxyleucine TFA methyl ester (1): 7.06 db,J=7.5 Hz (NH); 5.04 dd,J=3.3, 8.6 Hz (H-3); 4.97 dd,J=3.3, 7.5 Hz (H-2); 3.84 s (3H, COOCH3); 2.18 m,J=6.7, 6.8, 8.6 Hz (H-4); 1.11 d,J=6.8 Hz (CH3); 0.97 d,J=6.7 Hz (CH3). 5,5-Dichloroleucine TFA methyl ester (3): 6.75 db,J=8.2 Hz (NH): 5.77 d,J=2.9 Hz (H-5); 4.70 ddd,J=3.1, 4.0, 8.2 Hz (H-2); 3.81 s (COOCH3); 2.15 m (H-4); 2.09 ddb,J=3.1, 10 Hz (H-3a); 1.97 ddb,J=4.0, 10 Hz (H-3b); 1.23 d,J=6.5 (CH3). 3-Hydroxylysine TFA methyl ester (6): 6.96 db,J=8.8 Hz (2-NH); 6.44 mb (6-NH); 5.62 m (H-3), 4.92 dd,J=2.2, 8.8 Hz (H-2); 3.81 s (3H, COOCH3); 3.42 m (H-6a, H-6b); 1.74 m (4H; 4-CH2 and 5-CH2).
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HPLC employed a Waters gradient system (two model 6000A pumps, model 660 solvent programmer, and model 440 UV detector) with reversed-phase ODS semipreparative column (10 mn 1D×25 mm) at a flowrate of 3.0 ml/min. Solvent program: 0–100% acetonitrile in water in 20 min with monitoring at 254 nm. Retention times (min): unidentified component, 6.7; TFA methyl ester derivative, 10.1.
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We wish to thank Prof. D. Arigoni and his coworkers for informing us that they have independently determined the structures described above, and that they have also completed the assignment of the entire victorin structure.
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Gloer, J.B., Meinwald, J., Walton, J.D. et al. Studies on the fungal phytotoxin victorin: Structures of three novel amino acids from the acid hydrolyzate. Experientia 41, 1370–1374 (1985). https://doi.org/10.1007/BF01949994
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DOI: https://doi.org/10.1007/BF01949994