Novel thidiazuron-derived inhibitors of cytokinin oxidase/dehydrogenase

Abstract

Two new TDZ derivatives (HETDZ and 3FMTDZ) are very potent inhibitors of CKX and are promising candidates for in vivo studies. Cytokinin hormones regulate a wide range of essential processes in plants. Thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5-yl urea, TDZ), formerly registered as a cotton defoliant, is a well known inhibitor of cytokinin oxidase/dehydrogenase (CKX), an enzyme catalyzing the degradation of cytokinins. TDZ thus increases the lifetime of cytokinins and their effects in plants. We used in silico modeling to design, synthesize and characterize twenty new TDZ derivatives with improved inhibitory properties. Two compounds, namely 1-[1,2,3]thiadiazol-5-yl-3-(3-trifluoromethoxy-phenyl)urea (3FMTDZ) and 1-[2-(2-hydroxyethyl)phenyl]-3-(1,2,3-thiadiazol-5-yl)urea (HETDZ), displayed up to 15-fold lower IC 50 values compared with TDZ for AtCKX2 from Arabidopsis thaliana and ZmCKX1 and ZmCKX4a from Zea mays. Binding modes of 3FMTDZ and HETDZ were analyzed by X-ray crystallography. Crystal structure complexes, solved at 2.0 Å resolution, revealed that HETDZ and 3FMTDZ bound differently in the active site of ZmCKX4a: the thiadiazolyl ring of 3FMTDZ was positioned over the isoalloxazine ring of FAD, whereas that of HETDZ had the opposite orientation, pointing toward the entrance of the active site. The compounds were further tested for cytokinin activity in several cytokinin bioassays. We suggest that the combination of simple synthesis, lowered cytokinin activity, and enhanced inhibitory effects on CKX isoforms, makes 3FMTDZ and HETDZ suitable candidates for in vivo studies.

New Urea Derivatives Are Effective Anti-senescence Compounds Acting Most Likely via a Cytokinin-Independent Mechanism

“…The only exception to this rule is the compounds described in this work. Although many thidiazuron derivatives have been synthesized (e.g., Yip and Yang, 1986 ; Nisler et al, 2016 ), none of the compounds reported here have previously been described. All of the synthesized compounds were characterized by high resolution Mass Spectrometry and 1 H NMR (Supplementary Tables S1 , S2 ).…”

“…The compound 1,2,3-thiadiazol-5-ylamine was the starting material for the synthesis of 5-isocyanato-1,2,3-thiadiazole, which was prepared as described by Nisler et al ( 2016 ). The compounds TD- t Z, TD-iP, TD-DHZ and compounds 1-15 were prepared by mixing 5-isocyanato-1,2,3-thiadiazole and the corresponding commercially available amine under mild heat (30 to 60°C) in tetrahydrofuran in the presence of a catalytic amount of triethylamine (Goldschmidt and Bardach, 1892 ).…”

Role of Cytokinins in Senescence, Antioxidant Defence and Photosynthesis

“…This may be due to a number of reasons, e.g., TDZ exhibits strong CK activities in several bioassays, however in contrast to t Z, cannot be degraded by cytokinin oxidase dehydrogenase (CKX, a key enzyme involved in CK degradation in plants [56,57]). TDZ cannot be deactivated by O -glucosylation and can maintain a higher content of endogenous CKs in plant tissue by inhibiting the function of CKX [58,59,60]. Owing to its high CK and particularly antisenescence activity, TDZ has been extensively studied and used to prolong the life of cut flowers [55].…”

Chemical Defoliant Promotes Leaf Abscission by Altering ROS Metabolism and Photosynthetic Efficiency in Gossypium hirsutum

“…Applying chemical defoliants before harvesting can promote the shedding of cotton leaves as well as promote boll opening and thus effectively reduce the content of impurities in raw cotton and enhance the harvest efficiency, especially for the mechanically harvested cotton [25,27]. Thidiazuron (a synthetic cytokinin-like molecule, TDZ) is the main component of cotton chemical defoliants that widely used in most cotton-producing countries currently [28]. However, the mechanism of TDZ inducing cotton leaf shedding is not completely clear.…”