Abstract
A sequential multi-component reaction of the nitroketene dithioacetals, cysteamine hydrochloride, isatin and different CH-acids is described. This efficient method provides new functionalized thiazolo pyridine-fused spirooxindoles and thiazolo pyridopyrimidine-fused spirooxindoles in good yields. In the case of using isatin derivatives (5-bromoisatin and 5-chloroisatin), the reaction was carried out by using nano-SiO2 (20 mol%) as an effective heterogeneous Lewis acid promoter. This type of reaction provides a range of skeletally different polycyclic spiro thiazole-based heterocyclic structures and represents attractive advantages including straightforward one-pot operation under the catalyst-free condition and simple workup procedures without using tedious purification procedure.
Highlights
Spiroheterocycles moieties frequently observed in central skeletons of numerous bioactive natural alkaloids and due to its high medicinal properties, occupied a specific region in the heterocyclic field, and they have become valuable therapeutic targets in drug discovery layouts because of inherent three-dimensional character and capability to functionalities in all three dimensions [1, 2]
Spirooxindoles are known as a subclass of indole that 3-carbon position of indole sharing in the constitution of spiroindole structures which makes them as core building blocks of many synthetic drugs [4, 5], and natural functionalized organic compounds which raise their biological properties [6, 7]
Spirooxindoles are valuable synthetic targets in organic chemistry and pharmacological research fields due to their remarkable biological properties including antimicrobial [8], antitumor [9], antidiabetic [10], potential antileukemic, local anesthetic [11], antifungal activities [12] and can use as intermediates in synthetic steps for many types of medicinal precursors [13], e.g. spirotryprostatin A exhibit microtubule assembly inhibition while isopteropodine and pteropodine adjust the action of muscarinic serotonin receptors (Figure 1) [5,11]
Summary
Spiroheterocycles moieties frequently observed in central skeletons of numerous bioactive natural alkaloids and due to its high medicinal properties, occupied a specific region in the heterocyclic field, and they have become valuable therapeutic targets in drug discovery layouts because of inherent three-dimensional character and capability to functionalities in all three dimensions [1, 2]. The previous literature show the formation of the compounds with analogous structures, designing novel practical, fine, efficient and catalyst-free synthetic methods for these new structurally skeleton spiro thiazole-based heterocycles is highly desirable. General interest in spiro thiazole-based heterocycles structures comes from their structural properties and from their biological applications, so introducing new synthetic procedures for the synthesis of spiro thiazole-based heterocycles has been an active field of chemical research for well over a century and would be beneficial to develop new therapeutic agents [21, 22, 23]. In continuation of our work on the expansion of new methods to construct potential biologically active heterocycles [24, 25, 26] and considering typical substituent impacts on bioactive properties, we report new synthetic approaches to sulfur-containing spiro heterocycle molecules. The products generally containing unique sulfur atom and were acquired in good efficiencies, with simple workup processes and easy isolation
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