Abstract
The extract of the Nigerian lichen Ramalina farinacea showed
inhibitory activity against the respiratory syncytial virus in a preliminary
assay. A follow-up chemical investigation of this lichen led to the
isolation of thirteen phenolic compounds (1–13), including one
new hydroquinone depside, designated 5-hydroxysekikaic acid (1), and
one new orsellinic acid derivative, 2,3-dihydroxy-4-methoxy-6-pentylbenzoic
acid (8). Their structures were unambiguously determined by analysis
of 1D and 2D NMR and mass spectroscopic data, as well as by comparison with
literature data. Compound 1 was found to partially convert to a
1,4-benzoquinone derivative (1a) during storage. The antiviral
activities of the isolated compounds were evaluated against the respiratory
syncytial virus. Among them, sekikaic acid (2) showed potent
inhibition towards a recombinant strain rg respiratory syncytial virus
(IC50 5.69 µg/mL) and respiratory syncytial virus A2 strain
(IC50 7.73 µg/mL). The effect of sekikaic acid on the cell
viability of HEp2 and Vero cell lines was investigated, and the time of
addition assay revealed that sekikaic acid clearly interferes with viral
replication at a viral post-entry step, which is over 1.3-fold more active
than the control ribavirin at 4 hours postinfection addition. Furthermore,
sekikaic acid did not display virucidal activity at concentrations below the
TC50, whereas the parental extract did.
Key words
Ramalinaceae -
Ramalina farinacea
- structure elucidation - sekikaic acid - antiviral - respiratory syncytial virus