GUN00775, also known as N-(m-PEG4)-3,3-Dimethyl-3H-indole-N'-(acid-PEG3)-Benzothiazole Cy5, is a PEG derivative containing a cyanine dye with excitation emission maximum 649 667 nm and a free terminal carboxyl acid. Terminal carboxylic acid can react with primary amine groups in the presence of of activators (e.g. EDC, or DCC) to form a stable amide bond. The hydophilic PEG spacer increases solubility in aqueous media. This product has no formal name at the moment. For the convenience of communication, a temporary code name was therefore proposed according to MedKoo Chemical Nomenclature (see web page: https: www.medkoo.com page naming).