Abstract
Introduction: The preparation of model 6-chloro-5-nitrothieno[2,3-c]pyridazines incorporating (2'-halo-5'-nitrophenyl) entity is described. Interaction of these substrates with N'-(aryl)benzothiohydrazides, in the presence of triethylamine, followed a formal [4+1] annulation, furnishing the respective 1,3,4-thiadiazoline–benzothiazolo [3,2-b]pyridazine hybrids directly. This one-pot synthesis implies thiophene ring-opening and two consecutive intramolecular cyclizations. The structures of the synthesized new hybrids are supported by MS, NMR, and IR spectral data and further confirmed by single-crystal X-ray diffraction. These hybrids exhibit antiproliferative activity with notable selectivity against solid tumor cell lines (IC50: 4-18 μM).
Aims: This study aimed at exploring the scope and applicability of thiophene ring-opening reaction towards the synthesis of new thiadiazoline–[fused]tricyclic conjugates.
Background: α-Chloro-β-nitrothienopyridazine underwent ring-opening upon reacting with N'-(aryl)benzothiohydrazides generating 1,3,4-thiadiazoline–benzothiazolo[3,2-b]pyridazines.
Objective: This new thiophene ring-opening reaction is applied to the one-pot synthesis of thiadiazoline–benzothiazolo[3,2-b]pyridazine couples.
Method: A direct interaction of α-chloro-β-nitrothienopyridazine with N'-(aryl)benzothio-hydrazide at room temperature for 1-2 h occurred.
Result: a-Chloro-β-nitrothieno[2,3-c]pyridazines are suitable substrates for the facile synthesis of thiadiazoline–benzothiazolo[3,2-b]pyridazine hybrids.
Conclusion: This novel ring-opening reaction proceeds via formal [4+1] annulation and provides a versatile approach to various conjugated and/or fused five-membered heterocycles.
Keywords: Antitumor activity, N'-(Aryl)benzothiohydrazides, 6-chloro-5-nitrothieno[2, 3-c]pyridazines, formal [4+1] annulation, 1, 3, 4-thiadiazoline-[fused]tricyclic hybrids, heterocyclic rings.
Graphical Abstract
[http://dx.doi.org/10.1002/0471221902]
[http://dx.doi.org/10.1002/9781119941934]
[http://dx.doi.org/10.1021/cr5006974] [PMID: 25992465]
[http://dx.doi.org/10.1016/j.tet.2021.131957]
[http://dx.doi.org/10.1002/prac.19973390150]
[http://dx.doi.org/10.3891/acta.chem.scand.06-0189]
[http://dx.doi.org/10.1016/S0040-4039(01)97606-3]
[http://dx.doi.org/10.1515/znb-2019-0023]
[http://dx.doi.org/10.1038/nprot.2006.179] [PMID: 17406391]
[http://dx.doi.org/10.1107/S0021889808042726]
[http://dx.doi.org/10.1107/S2053273314026370] [PMID: 25537383]
[http://dx.doi.org/10.1107/S2053229614024218] [PMID: 25567568]
[http://dx.doi.org/10.1139/v96-148]
[http://dx.doi.org/10.1080/10426509208049173]
[http://dx.doi.org/10.1139/v93-078]
[http://dx.doi.org/10.1002/anie.201809432] [PMID: 30225899]
[http://dx.doi.org/10.1021/om1009022]
[http://dx.doi.org/10.1039/c0dt01319f] [PMID: 21412554]
[http://dx.doi.org/10.1039/C6CS00296J]
[http://dx.doi.org/10.1021/jo00031a035]
[http://dx.doi.org/10.2165/00003495-199652040-00010] [PMID: 8891467]
[http://dx.doi.org/10.1080/14756366.2018.1553040] [PMID: 30734592]
[http://dx.doi.org/10.1016/j.ejmech.2014.10.059] [PMID: 25462241]
[http://dx.doi.org/10.1080/14756366.2019.1698036] [PMID: 31790602]
[http://dx.doi.org/10.1134/S1068162020050155]
[http://dx.doi.org/10.1016/j.ejmech.2014.12.035] [PMID: 25553540]
[http://dx.doi.org/10.1021/cr400131u] [PMID: 24716666]
[http://dx.doi.org/10.1080/13543776.2017.1272575 ] [PMID: 27976971]