Clinically available antifungal drugs have therapeutic limitations due to toxicity, narrow spectrum of activity, and intrinsic or acquired drug resistance. Thus, there is an urgent need for new broad-spectrum antifungal agents with low toxicity and a novel mechanism of action. In this context, we have successfully identified several highly promising lead compounds, i.e., aromatic N’-(salicylidene)carbohydrazides, exhibiting excellent antifungal activities against Cryptococcus. neoformans, Candida albicans, Aspergillus fumigatus and several other fungi both in vitro and in vivo. Building upon these highly promising results, 71 novel N’-(salicylidene)heteroarenecarbohydrazides 5 were designed, synthesized and their antifungal activities examined against fungi. Among these 71 novel heteroarenecarbohydrazides 5, 11 of them bear fused bicyclic heteroaromatic groups in ring A and 60 of them bear 5- and 6-membered ring oxygen-, sulfur- and nitrogen-heteroaromatic groups in ring A. It was found that all of the 11 compounds bearing fused bicyclic heteroaromatic groups in ring A did not show good potency. Among the 60 new carbohydrazides 5 bearing monocyclic heteroaromatic groups, 28 of them exhibited high potency (MIC80 £ 1 mg/mL), which were further examined for their fungicidal or fungistatic activity base on a time-kill assay in vitro, as well as for their selectivity to fungi in comparison to human cells. Out of those 28 compounds, 20 were found to be fungicidal and 8 fungistatic. Most of the compounds bearing bromofuran and bromothiophene groups as ring A showed high potency with high selectivity, i.e., low cytotoxicity to human cells. Based on the SAR study, four highly promising lead compounds, i.e., 5.13a, 5.6a, 5.6b and 5.7b, were identified, which exhibited excellent potency and time-kill profiles against C. neoformans with exceptionally high selectivity indices (SI ≥500).For the SAR study, we also employed quantitative structure-activity relationship (QSAR) analysis by taking advantage of the accumulated data on a large number of aromatic and heteroaromatic N’-(salicylidene)carbohydrazides. This strategy successfully led to rational design and selection of promising compounds for chemical synthesis and biological evaluation
