(fye'' soe stig' meen).
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C15H21N3O2 275.35

Pyrrolo[2,3-b]indol-5-ol, 1,2,3,3a,8,8a-hexahydro-1,3a,8-trimethyl-, methylcarbamate (ester), (3aS-cis).
1,2,3,3a,8,8a-Hexahydro-1,3a,8-trimethylpyrrolo[2,3-b]indol-5-yl methylcarbamate [57-47-6].
» Physostigmine is an alkaloid usually obtained from the dried ripe seed of Physostigma venenosum Balfour (Fam. Leguminosae). It contains not less than 97.0 percent and not more than 102.0 percent of C15H21N3O2, calculated on the dried basis.
Packaging and storage— Preserve in tight, light-resistant containers.
USP Reference standards 11
USP Physostigmine Salicylate RS Click to View Structure
Identification— It meets the requirements of the test for Identification—Organic Nitrogenous Bases 181, USP Physostigmine Salicylate RS being used, and 1 g of sodium bicarbonate being used in place of the 2 mL of 1 N sodium hydroxide specified.
Specific rotation 781S: between 236 and 246 (= 365 nm).
Test solution: 10 mg per mL, in methanol.
Loss on drying 731 Dry it over silica gel for 24 hours: it loses not more than 1.0% of its weight.
Residue on ignition 281: negligible, from 100 mg.
Readily carbonizable substances 271 Dissolve 100 mg in 5 mL of sulfuric acid: at the end of 5 minutes the solution has no more color than Matching Fluid I.
Assay— Dissolve about 175 mg of Physostigmine, accurately weighed, in 25 mL of chloroform. Add 25 mL of glacial acetic acid, and titrate with 0.02 N perchloric acid in dioxane VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.02 N perchloric acid is equivalent to 5.507 mg of C15H21N3O2.
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