2-Hydroxycarbazole is a compound structurally related to the Ca2+-mobilizing marine toxin, 9-methyl-7-bromoeudistomin. Room temperature electronic absorption and fluorescence spectra of 2-hydroxycarbazole has been studied in concentrated aqueous potassium hydroxide solutions. It undergoes chemoselective N-alkylation using NaH as a base in a THF-DMF solvent system. Application： Carbazol has been found possible to distinguish between heparin, heparin derivatives, and other polyuronides of connective tissue. A new modification of the carbazole analysis is useful for determination of d-mannuronic acid in heteropolysaccharides. 2-Hydroxycarbazole was used in the synthesis of isochromene fused carbazol, (4aS,13bR)-2,5,5-trimethyl-3,4,4a,5,8,13b-hexahydroisochromeno[3,4-b]carbazole.