A 2,4′-linked tetrahydroxanthone dimer with protein tyrosine phosphatase 1B inhibitory activity from the Okinawan freshwater Aspergillus sp.

Aspergillus sp. TPU1343, maintained on a PDA plate, was inoculated into a 100 ml Erlenmeyer flask containing 50 ml of seed medium (2.0% glucose (Wako, Osaka, Japan), 0.50% polypeptone (Wako), 0.050% MgSO₄·7H₂O (Wako), 0.20% yeast extract (BD, Franklin Lakes, NJ, USA), 0.10% KH₂PO₄ (Wako), and 0.10% agar (Wako) in freshwater and adjusted to pH 6.0 before sterilization).¹ The flask was shaken reciprocally at 25 °C for 3 days to obtain the seed culture, which was then transferred to the production medium (3.0% sucrose (Wako), 3.0% soluble starch (Wako), 1.0% malt extract (BD), 0.30% Ebios (Asahi Food & Healthcare, Tokyo, Japan), 0.50% KH₂PO₄, and 0.050% MgSO₄·7H₂O in freshwater and adjusted to pH 6.0 before sterilization) and cultured at 25 °C for 7 days under agitation.

Acetone (20 l) was added to the culture broth (20 l) and filtered. The filtrate was concentrated in vacuo to remove acetone and extracted three times with EtOAc. The EtOAc extract was concentrated in vacuo to dryness, and the extract (35 g) was suspended in 30% CH₃OH in H₂O and applied on an ODS column (100 g). The ODS column was eluted stepwise with 30, 50, 70, 85 and 100% CH₃OH in H₂O (200 ml each × 2) to separate 10 fractions (Fr. 1–Fr. 10). Fr. 8 (the second 200 ml of the 85% CH₃OH eluate) was concentrated to give a dark black oil (241 mg), which was purified by preparative HPLC (column; inertsil ODS-3 (GL Science, Tokyo, Japan), 10 × 250 mm; mobile phase, 70% CH₃CN containing 0.05% TFA; detection, UV at 254 nm; flow rate, 2.0 ml min^–1) to afford 2.4 mg of compound 1 and 13 mg of secalonic acid F (2)^{1, 6} (Figure 1a).

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD