S-1 methanandamide is a CB1 receptor ligand.

The cannabinoid receptor type 1 (CB1), is a G protein-coupled cannabinoid receptor located mainly in the central and peripheral nervous system. CB1 is also expressed in several cells relating to metabolism, such as muscle cells, fat cells, liver cells, and the digestive tract. The CB1 receptor has been involved in the maintenance of homeostasis in health and disease, preventing the development of excessive neuronal activity, reducing pain and other inflammatory symptoms. Enhanced receptor expression has been identified in human hepatocellular carcinoma tumor samples and human prostate cancer cells [2].

S-1 methanandamide was a less potent than the C-1 (R) methyl isomer when binding with CB1 receptor. S-1 methanandamide inhibited electrically evoked contractions in isolated mouse vasa deferentia with an IC50 value of 230 nM. The binding affinity of S-1 methanandamide for CB1 receptors was less than that of AEA, with a Ki of 175 nM for the displacement of radiolabeled CP 55,940 [1].

References:
[1] Abadji V, Lin S, Taha G, et al.  (R)-methanandamide: a chiral novel anandamide possessing higher potency and metabolic stability[J]. Journal of medicinal chemistry, 1994, 37(12): 1889-1893.
[2] Howlett A C.  Cannabinoid receptor signaling[M]//Cannabinoids. Springer Berlin Heidelberg, 2005: 53-79.