Just a quick note to say that Daniel Lowe has released OPSIN v.2.9.0 , the first release since Oct 2023. This is now available via the EMBL-EBI OPSIN server . The release notes describe a mixture of minor bug fixes and improvements: Support for IUPAC recommended primed number-letter locants e.g. 2''a Command-line output now includes warnings e.g. ambiguity SMILES writer now starts from a * atom if one is present Added numbering to nicotine Correctly interpretation of locanted perhalo terms and perhaloalkylalkanes Improved additive bond formation for phosphoryl Corrected locants on tolyl and assume p-tolyl if unspecified triazine is now interpreted as 1,3,5-triazine if unspecified Corrected interpretation of dithiazolium Fixed rare SMILES writing bug where slashes could be inconsistent Fixed ylidenethenylidene being parsed as [ylidene][thenylidene] instead of [yliden][ethenylidene] Fixed bug in spiro superscript inferring when a bridge is length 0
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