The first total syntheses of the natural products lobaric acid (1) and its derivatives isolated from the Antarctic lichen Stereocaulon alpinum are reported in this study. Lobarin (3), with a pseudodepsidone structure, was synthesized first in 11 steps by utilizing an Ullmann aryl ether coupling reaction, and lobaric acid was synthesized in an additional three steps by a seven-membered lactonization reaction. Various derivatives were also obtained from the prepared lobaric acid, and the synthetic compounds exhibited significant PTP1B inhibitory activities.