as an attractive target for fungicide, bactericide and herbicide discovery [13-16]. Indeed, sulfonylureas (SUs) have been confirmed as
ultra-highly efficient and high selectivity herbicide targeting AHAS since the late 1970s [17]. Subsequently, Pang et al. reported the
crystal structures of Saccharomyces cerevisiae AHAS and Arabidopsis thaliana AHAS as the free enzyme and in complex with SUs
[
18-21]. These studies have elucidated the molecular basis for the inhibition of SUs toward AHAS, and provided us with powerful
information to rational design novel antifungal agents. Lee et al. reported that when the gene for AHAS was mutated in Cryptococcus
neoformans and Candida albicans, these fungi became attenuation of virulence due to the lack of BCAAs, further showing that AHAS is
a promising target for antifungal agents [16,22,23]. In addition, some compounds have been identified for antituberculosis activity
targeting AHAS, suggesting that AHAS is a potential target for the research of antimicrobial chemotherapy [24,25]. Nevertheless,
research on SUs for agricultural fungicide has been limited for decades.
In general, SUs compose by one ortho-substituted benzene ring, sulfonylurea bridge and one heterocyclic ring (either a pyrimidine (Z
=
CH) or triazine (Z = N)) (Fig. 1). As literatures showed that SUs’ activities were vigorously impacted by heterocycles or substitutents
[
12,26]. Additionally, pyrimidine was a key moiety in a wide variety of bioactive molecules including antifungal, antimicrobial,
anticancer and anti-inflammatory agents [27,28]. In our precious work, Chen et al. found that some SUs containing a bulk group at
pyrimidine moiety exhibited moderate to good inhibitory rates against plant pathogenic fungi [29,30]. Wei et al. also reported some
sulfonylureas containing an alkenyl moiety at benzene ring exhibited enhanced antifungal activities than chlorsulfuron [31].
Herein, in an effort to discover increasingly potent antifungal agents, great importance had been focused on the modifications to the
pyrimidine group. This work present rational designed and synthesized novel SU derivatives 9−11 based on the lead compounds (Fig. 1),
and their antifungal activity was evaluated in vitro. The structure-activity relationships were studied through comparative field analysis
(CoMFA) model, from which we tried to identify the key structural factors influence on inhibitory activity. In addition, molecular
docking was carried out to study the binding modes of 10k with yeast AHAS and explain the potential antifungal mechanism of the title
compounds.
Fig. 1. Design strategy of compounds 9−11.
As shown in Schemes S1 and S2 (Supporting information), N, N-dimethylformamide dimethyl acetal was refluxed with aryl ethanones
(1a−1c) for 4 h and then condensed with guanidine hydrochloride to generated the crude products 3a−3c, followed by recrystallize from
ethanol/hexane and obtained the arylpyrimidines [29]. 4a−4c and 5a−5c were facilely prepared from 3 with corresponding
o
N-halosuccinimide under reflux acetonitrile in reasonable yield, and 6a−6c were obtained under a lower temperature (40 C) [32]. The
key intermediates 4−6 were confirmed by 1D and 2D NMR spectra (Figs. S1-S3 in Supporting information) and indicated that
halogenation of pyrimidines 3 was regioselective occurred at the H-3 position and obtained the corresponding products (Fig. S4 in
Supporting information). The sulfonyl carbamates 8a−8d were prepared in excellent yield by treating sulfonamides 7a−7d with ethyl
chloroformate in the presence of powdered potassium carbonate in refluxing acetone. With intermediates 3−6 and 8 in hand, the title
compounds 9−11 were synthesized and purity according to the literatures in 60%−80% yield [29,33].
The in vitro inhibitory activity of compounds 9−11 was tested against ten phytopathogenic fungi at the dosage of 50 mg/L. The
screening data (Table S1 in Supporting information) indicated that most of the tested compounds showed broad-spectrum and excellent
fungicidal activities. For every fungus, all or some of the compounds were found to be more active than model compounds or positive
controls. In particular, 9j, 9m, 9n, 10k, 11d and 11e showed 87.5%, 87.5%, 87.5%, 87.5%, 80.0% and 87.5% inhibitory rate against C.
arachidicola, respectively, which were much higher than chlorothalonil (75.0%), carbendazim (<50%) and lead compound (≤50%). For
C. gramineum, 9e, 9i, 9k, 9l, 9n, 10f, 11i and 11k exhibited >90% antifungal activity and comparable to chlorothalonil (100%) and
carbendazim (100%). 9i, 11e, 11i and 11j showed more than 80% inhibitory rate against 6 fungi or even more. Over 14 title compounds
showed as high as 80% inhibition rate against C. gramineum and R. solani. Furthermore, the EC50 values of 11 SUs against C. gramineum
were equal to or better than chlorothalonil (0.016 μmol/L), 10k exhibited the best value (0.009 μmol/L, highlighted in Table S2 in
Supporting information).
The preliminary results in Table S1 showed that introduce bulk groups-aryl (p-toyl, 2-furyl and 2-thienyl) to pyrimidinyl 4-position in
an obvious improve the antifungal activities and broaden the antifungal spectrum compared to sulfometuron-methyl (≤50%). Comparing
the fungicidal activities of 9−11 against all the fungi, it exhibited that derivatives 11 had a little more activities and broader spectra than 9
and 10. It further demonstrated that substituents at 4-position of pyrimidine ring will influence the antifungal activities. In addition, the
existence of a halogen atom at pyrimidinyl 5-position was superior to a hydrogen (9e−9p versus 9a−9d), the approximately order is
R
1
=Br R
In comparison, the substituents at the benzene ring have a direct relationship between antifungal activities. Such as in series 11, the
-NO compounds exhibited higher activities and more broaden spectra than the analogues (11e versus 11f, 11g, 11h; 11i versus 11k, 11l
and 11m versus 11n, 11o, 11p), with the exception of 11j which was as effective as 11i. It also indicated that introducing nitro to the
1
=Cl R
1
=I R
1
=H.
2
2
Chen, Wei
