ROUTE DEVELOPMENT, ANTIVIRAL STUDIES, FIELD EVALUATION AND TOXICITY OF AN ANTIVIRAL PLANT PROTECTANT NK0238

Highlights

• Developed a two-step synthetic route to anti-plant-virus candidate NK0238.

• NK0238 exhibited a broad antivirus spectrum in greenhouse.

• NK0238 showed comparable antivirus activities as controls in field trials.

• NK0238 was safe to birds, fish, bees and silkworms.

• NK0238 has a very good prospect in commercial development.

Abstract

It has previously been shown that tryptophan, the biosynthesis precursor of Peganum harmala alkaloids, and its derivatives have anti-TMV activity both in vitro and in vivo. Further exploration of this led to the identification of NK0238 as a highly effective agent for the prevention and control of diseases caused by plant viruses, but the existing routes are unsuitable for its large-scale synthesis. This study optimized a route for two-step synthesis of this virucide candidate via reaction of l-tryptophan with triphosgene to produce l-tryptophan-N-carboxylic anhydride, which then reacts with n-octylamine to give NK0238 at up to 94% yield and nearly 97% HPLC purity. In addition, the route was used for the preparation of NK0238 on a>40 g scale permitting further assessment of its antivirus activity in the greenhouse and field experiments, and toxicity tests. NK0238 exhibited useful antiviral activities against a variety of viruses both in greenhouse and field experiments. The toxicity tests showed that NK0238 was not acutely toxic to birds, fish, honey bees and silkworms. The optimized route provides a solid foundation for its large-scale synthesis and subsequent efficacy and toxicity studies, its excellent activity and safety make NK0238 a promising drug candidate for further development.

Graphical abstract

Keywords

antiviral plant protectant / antiviral in the greenhouse / field evaluation / l-trp-NCA / synthesis optimization / toxicity tests

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Supplementary materials

The online version of this article at https://doi.org/10.15302/J-FASE-2021390 contains supplementary materials. Mechanisms of reactions of tryptophan with phosgene and triphosgene (Fig. S1); optimization of conditions for for synthesis of L-NAC from phosgene (Table S1); screening of quenchers for synthesis of L-NAC from phosgene (Table S2); ¹H and ¹³C NMR Spectra of L-trp-NCA, NK0238, and byproduct (Figs. S2–S7); HPLC standard curve for NK0238 (Fig. S8); HPLC spectrum of NK0238 in scaled-up reaction (Fig. S9); Chiral chromatographic separation (Table S3, Fig. S10–S11); the inactivation, protective and curative effect against TMV (Fig. S12); and procedures for the antivirus and field trial are provided in the supplementary materials.

Acknowledgements

The authors are grateful to the National Natural Science Foundation of China (21977056, 21732002), the Fundamental Research Funds for the Central Universities, Nankai University (63201043) for generous financial support for their programs.

Compliance with ethics guidelines

Wentao Xu, Hao Tian, Hongjian Song, Yuxiu Liu, Yongqiang Li, and Qingmin Wang declare that they have no conflicts of interest or financial conflicts to disclose. This article does not contain any studies with human or animal subjects performed by any of the authors.

RIGHTS & PERMISSIONS

The Author(s) 2021. Published by Higher Education Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0)