Lysergic acid 2-butyl amide (2-Butyllysergamide, LSB) is an analogue of LSD originally developed by Richard Pioch at Eli Lilly in the 1950s, but mostly publicised through research conducted by the team led by David E. Nichols at Purdue University. It is a structural isomer of LSD, with the two ethyl groups on the amide nitrogen having been replaced by a single sec-butyl group, joined at the 2-position. It is one of the few lysergamide derivatives to exceed the potency of LSD in animal drug discrimination assays, with the (R) isomer having an ED50 of 33nmol/kg for producing drug-appropriate responding, vs 48nmol/kg for LSD itself. The corresponding (R)-2-pentyl analogue has higher binding affinity for the 5-HT1A and 5-HT2A receptors, but is less potent in producing drug-appropriate responding, suggesting that the butyl compound has a higher efficacy at the receptor target. The drug discrimination assay for LSD in rats involves both 5-HT1A and 5-HT2A mediated components, and while lysergic acid 2-butyl amide is more potent than LSD as a 5-HT1A agonist, it is slightly less potent as a 5-HT2A agonist, and so would probably be slightly less potent than LSD as a hallucinogen in humans. The main use for this drug has been in studies of the binding site at the 5-HT2Areceptor through which LSD exerts most of its pharmacological effects, with the stereoselective activity of these unsymmetric monoalkyl lysergamides foreshadowing the subsequent development of compounds such as lysergic acid 2,4-dimethylazetidide (LSZ).
^US patent 2997470, Richard P. Pioch, "LYSERGIC ACID AMIDES", published 1956-03-05, issued 1961-08-22
^Oberlender R, Pfaff RC, Johnson MP, Huang XM, Nichols DE. Stereoselective LSD-like activity in d-lysergic acid amides of (R)- and (S)-2-aminobutane. Journal of Medicinal Chemistry. 1992 Jan 24;35(2):203-11. PMID 1732537
^Monte AP, Marona-Lewicka D, Kanthasamy A, Sanders-Bush E, Nichols DE. Stereoselective LSD-like activity in a series of d-lysergic acid amides of (R)- and (S)-2-aminoalkanes. Journal of Medicinal Chemistry. 1995 Mar 17;38(6):958-66. doi:10.1021/jm00006a015PMID 7699712
^David E. Nichols. LSD and Its Lysergamide Cousins. The Heffter Review of Psychedelic Research. 2001;2:80-87.