Thuwalallenes A-E (1-3, 5 and 8) and thuwalenynes A-C (4, 6, 7), new C₁₅ acetogenins featuring uncommon ring systems, along with cis-maneonene D (9), thyrsiferol (10) and 23-acetyl-thyrsiferol (11) were isolated from the organic extract of a population of the red alga Laurencia sp., collected at Rose Reef off the village of Thuwal in the Red Sea waters of the Kingdom of SaudiArabia. The structure elucidation of the isolated natural productswas based on extensive analysis of their spectroscopic data. Compounds 1-6, 8, 10 and 11 were evaluated for their anti-inflammatory activity by quantifying nitric oxide (NO) release in response to TLR4 stimulation in macrophages. Besides compound 4 that did not exhibit any activity, all other tested metabolites inhibited NO production from activated macrophages. Among them, thyrsiferol (10) and 23-acetylthyrsiferol (11) displayed activity with IC₅₀ values in the low nM scale without cytotoxicity.