Paper
RSC Advances
Conclusions
In summary, a series of new BTZs containing hexahydropyrrolo
[3,4-c]pyrrol moiety were designed and synthesized based on the
spiro-BTZ IMB1603 discovered in our lab. Many of them
exhibited potent in vitro anti-TB activity. Especially, compounds
11 and 24 were found to display excellent anti-MTB activity
against the drug-sensitive MTB strain H37Rv (MIC < 0.035 mM),
and also potent anti-MDR-MTB activity against the two drug-
resistant clinical isolates (MIC, 0.053–0.102 mM). In addition,
BTZs 11 and 24 showed low cytotoxicity (CC50 > 200 mM), and
exhibited better water solubility than PBTZ169, suggesting both
of them may serve as new and promising candidates for further
antitubercular drug discovery. The molecular docking results
suggested that 11 mimicked the binding pattern of PBTZ169 in
the active site of DprE1. Studies to determine the PK proles
and in vivo efficacy of 11 and 24 are currently under way.
Conflicts of interest
There are no conicts to declare.
Fig. 2 Overlay of the docking hydroxylamine intermediate of 11
(carbons are green) on the crystallized semimercaptal adduct (carbons Acknowledgements
are off white). (A) The overall view of the binding pattern; (B) close-up
view of the DprE1 active site.
This work is supported by the National Mega-project for Inno-
vative Drugs (2018ZX09721001-004-007; 2018ZX09711001-007-
002), National Natural Science Foundation of China (81872753).
inhibiting 50% growth (CC50) as compared to a no-treatment
control and the results were reported in Table 4. Most of the
tested targets displayed higher cytotoxicity than that of
PBTZ169. However, to our delight, compounds 11 and 24
showed low cytotoxicity (CC50 > 200 mM). Subsequently,
considering acidic gastrointestinal environments, these new
BTZs were evaluated for their water solubility at pH 2 (0.01 M
HCl solution) by using an HPLC-UV method.23 All of them dis-
played good solubility (1.82–3.50 mg mLꢀ1), and were more
water-soluble than PBTZ169 (0.90 mg mLꢀ1).
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the same site. Thus, we predicted the binding mode of
compound 11 in the DprE1 dimer–dimer interface (PDB code:
4NCR) through molecular docking using CDDOCK module of
Discovery Studio 3.5. Since the intrinsic ligand PBTZ169 was
crystallized as a covalent adduct with DprE1, it was necessary
to optimize the docking protocol of 11 into DprE1. Briey, the
benzothiazinone ligand (semimercaptal) present in the
crystal structure was deleted and no hydrogen was added to
the formed thiolate of Cys 387. The reduced hydroxylamine
form of 11 was docked in the same binding pocket forming
the semimercaptal adduct as reported before.17 The docking
study revealed that 11 mimicked the binding pattern of
PBTZ169 in the active site of DprE1 (Fig. 2B). The (tri-
uoromethoxy)benzyl moiety of 11 was placed outside the
pocket and showed high exibility as the cyclohexylmethyl
moiety of PBTZ169, whereas the BTZ core occupied the inner
part of the cavity (Fig. 2A).
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RSC Adv., 2020, 10, 14410–14414 | 14413