Abstract
A series of new 2,5-disubstituted 1,3,4-oxadiazoles was synthesized under conventional thermal heating and microwave irradiation conditions through the reaction of acyl hydrazides with N- protected α-amino acid in presence of a small amount of POCl3. Heterocycles were obtained in moderate to good yields and in relatively short reaction times.
Highlights
1,3,4-Oxadiazoles and their derivatives constitute an important class of heterocyclic compounds as they have attracted significant interest in medicinal and pesticide chemistry as well as polymer and material science
As part of our growing interest in using α-amino acids as chiral building blocks in organic synthesis,[36,37,38] and in connection with the increasing importance of the synthesis of small libraries of compounds with programmed variations of substituents, we describe an easy and inexpensive one-pot synthetic route for the preparation of a set of chiral N-protected chiral α-amino acid derived 1,3,4-oxadiazoles under conventional thermal heating and microwave irradiation, as depicted in the Scheme 1
With the reaction conditions optimized, we extended the protocol to a broader range of protected amino acids 1-6 as shown in Figure 1 and to a variety of commercial hydrazides in the presence of phosphorus oxychloride using conventional heating protocols and microwave (Scheme 2)
Summary
1,3,4-Oxadiazoles and their derivatives constitute an important class of heterocyclic compounds as they have attracted significant interest in medicinal and pesticide chemistry as well as polymer and material science. The most common synthetic protocol toward the preparation of these compounds involves the dehydrative cyclization of diacylhydrazides using usually strong acidic reagents such as thionyl chloride,[20] phosphorus pentoxide,[21] phosphorus oxychloride,[22,23,24,25] and sulfuric acid.[26]. These molecules are expected to have the same therapeutic effects as natural peptide counterparts, with the added advantage of metabolic stability. Amino acids have emerged as important building blocks for the synthesis of a range of different compounds.[29,30,31] the interest on the biological and medicinal properties of chalcogen amino acids has been increasingly appreciated, mainly due to their antioxidant,[32] antitumor,[33] antimicrobial,[34] and antiviral[35] properties
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