Aquastatin A

HIV-1 integrase is one of the three enzymes that are critical for replication and spread of HIV and its inhibition is one of the most promising new drug targets for anti-retroviral therapy with potential advantage over existing therapies. This paper describes the isolation and structure elucidation of exophillic acid, a novel dimeric 2,4-dihydroxy alkyl benzoic acid, derived from Exophiala pisciphila, a fungus isolated from a soil sample collected in Georgia, USA. Exophillic acid (1) and aquastatin A (2), a related compound, inhibited the strand transfer reaction of HIV-1 integrase with IC50 values of 68 and 50 microM, respectively.

Bacterial enoyl-acyl carrier protein (ACP) reductase has been confirmed as a novel target for antibacterial drug development. In this study, we determined that a fungal metabolite from Sporothrix sp. FN611 potently inhibited the enoyl-ACP reductase (FabI) of Staphylococcus aureus. Its structure identified the metabolite as aquastatin A by the MS and NMR data. Aquastatin A inhibited S. aureus FabI with an IC(50) of 3.2 microM. It also prevented the growth of S. aureus and methicillin-resistant Staphylococcus aureus (MRSA) with minimum inhibitory concentration of 16-32 microg/ml. Aquastatin A also exerted an inhibitory effect against the FabK isoform, an enoyl-ACP reductase of Streptococcus pneumoniae, with an IC(50) of 9.2 microM. The degalactosylation of aquastatin A did not affect the FabI and FabK-inhibitory or antibacterial activities, thereby suggesting that the sugar moiety within its molecular structure was not involved in these activities. The inhibitory effects of aquastatin A and its degalactosylated derivative on enoyl-ACP reductases and bacterial viability are reported for the first time in this study; these effects point to the potential that aquastatin A may be developed into a new broad-spectrum antibacterial and anti-MRSA agent.

In the course of bioassay-guided study on the EtOAc extract of a culture broth of the marine-derived fungus Cosmospora sp. SF-5060, aquastatin A (1) was isolated as a protein tyrosine phosphatase 1B (PTP1B) inhibitory component produced by the fungus. The compound was isolated by various chromatographic methods, and the structure was determined mainly by analysis of NMR spectroscopic data. Compound 1 exhibited potent inhibitory activity against PTP1B with IC(50) value of 0.19muM, and the kinetic analyses of PTP1B inhibition by compound 1 suggested that the compound is inhibiting PTP1B activity in a competitive manner. Aquastatin A (1) also showed modest but selective inhibitory activity toward PTP1B over other protein tyrosine phosphatases, such as TCPTP, SHP-2, LAR, and CD45. In addition, the result of hydrolyzing aquastatin A (1) suggested that the dihydroxypentadecyl benzoic acid moiety in the molecule is responsible for the inhibitory activity.