Intestinal commensal fungi are vital to human health, and their secondary metabolites play a key role in the reciprocal relationship. In the present study, the first example of 2,3-seco ergot alkaloids belonging to clavine-type were isolated from the fermentation of human intestinal fungus Aspergillus fumigatus CY018, including two pairs of diastereoisomers, secofumigaclavines A (3) and B (4) and secofumigaclavines C (5) and D (6), one analogue features a highly unsaturated skeleton, secofumigaclavine E (7), along with two known ones, fumigaclavines C (1) and D (2). Their structures were identified based on extensive spectroscopic data in a combination of quantum chemical calculations. Moreover, a single-step operation of semi-synthetic reaction based on riboflavin (RF)-dependent photocatalysis was performed to obtain the novel 2,3-seco ergot alkaloids 3 and 5 from their biosynthetic precursors 1 and 2. All the isolated compounds were evaluated for their anti-inflammatory activity. Among them, secofumigaclavine B (4) could bind to MD2 with a low micromole level of the equilibrium dissociation constant measured by surface plasmon resonance (SPR), and suppress TLR4-mediated NF-κB signaling pathway in RAW264.7 cells, resulting in its anti-inflammatory effect. Molecular dynamics revealed that amino acid residue Tyr131 played a key role in the interaction of secofumigaclavine B (4) with MD2. These findings suggested that secofumigaclavine B (4) could be considered as a potential candidate for the development of MD2 inhibitors.
Keywords: Ergot alkaloids; Human intestinal fungus; MD2; Semisynthesis; TLR4.
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