Systemic fungal infections are a growing problem in contemporary medicine and few drugs are licensed for therapy of invasive fungal infections. Differences between fungi and humans, like the presence of a cell wall in fungal cells, can be explored for designing new drugs. (1,3)-β-D-glucan synthase, an enzyme that catalyzes the synthesis of (1,3)-β-D-glucan, a structural and essential component of the fungal cell wall, is absent in mammals and this makes it an excellent target for the development of new antifungal agents. Papulacandins are a family of natural antifungal agents targeting (1,3)-β-D-glucan synthase. In this study we describe the synthesis and biological evaluation of two new Papulacandin analogs as potential (1,3)-β-D-glucan synthase inhibitors.

A series of six new palmitic acid-based neoglycolipids related to Papulacandin D were synthesized in five steps, resulting in good yields, and they were evaluated against Candida spp. All twelve synthetic intermediates were also evaluated. The synthesis involved the initial glycosylation of two phenols (4-hydroxy-3-methoxybenzaldehyde and 3-hydroxybenzaldehyde) via their reaction with peracetylated glucosyl bromide. This was followed by deacetylation with potassium methoxide/metanol solution and the protection of two hydroxyls (C4 and C6 positions) of the saccharide unit as benzilidene acetals (10-11). The next step involved the acylation of the acetal derivatives with palmitic acid, thereby affording a mixture of two isomers mono-acylated at the C2 and C3 positions and a di-acylated product (12-17). After being isolated, each compound was subjected to the removal of the acetal protecting group to yield the papulacandin D analogues 18-23. Three compounds showed low antifungal activity against two species: C. albicans (compounds 7 and 23) and C. tropicalis (compound 17) at 200 µg mL−1.