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(I have a background in organic chemistry as well) I somewhat disagree with this. Measuring chemical similarity is notoriously difficult, see these two interesting blog posts from a cheminformatic angle [0][1]. The molecules are not only pharmacologically similar but even chemically at least somewhat similar, perhaps in the same way a dog has much more similarities with a flying squirrel than with, let's say a church. I would argue the main active molecule [2] is relatively similar to LSD (compared to other well known psychedelics) due the presence of the tetrahydropyridine unit, which is also present in LSD, albeit connected to the 3 position of the indole in a different way. Also, there is a pharmaco*phor*ic similarity: positively charged N and 5-6 fused aromatic ring oriented in the same way with some degree of rigidity (though you could argue this is just a roundabout way to bin it in a category of 5ht2a binders). So in this way, I feel that it has something like an LSD-based design philosophy to it. Quantitatively, making use of one of the most common similarity metrics, the Tanimoto similarity of ECFP4 fingerprints, the similarities to LSD, psilocin, DMT and mescaline are respectively 0.17,0.15,0.18 and 0.07. In other words, the similarity is low to all compounds and the indole derivatives are about equally far removed from the compound from TFA, although a bit closer than mescaline. The numbers probably rather follow your line of reasoning. Finally, I'd also like to remark that I consider the fact they generated quite novel chemical matter a plus: most of the people working on generating new 5HT2A agonists are currently using quite conservative classic SAR approaches, for example creating constrained (e.g. Lophora's azetidines) or deconstructed versions (e.g. Delix's ring opened LSD variants and ibogaine analogs) of better known compounds, or even just prodrugs of known compounds (Field trip's FT104 is a 4-HO-DIPT prodrug). This will also make it easier for them to fight patent challenges if this series of compounds will lead to a clinical candidate. [0] http://www.dalkescientific.com/writings/diary/archive/2020/0... [1] http://www.dalkescientific.com/writings/diary/archive/2020/0... [2] The SMILES string of molecule 69 from the paper, which is the one from the cryo EM structure: `C[C@@H]1C=C(c2c[nH]c3ncccc23)CNC1` |