Macroscopic— Cat's Claw is a woody vine with a main stem up to 20 cm in diameter and 30 m long. The branches are obtusely quadrangular and generally puberulous. Stipules in the buds are densely tomentose in the upper side (different from U. guianensis in which the stipules are glabrous) with the hairs, often with curved tips, meshed together and with the longer hairs of the leaf helping to connect the pair of stipules along the margins, but split when older (different from U. guianensis in which the stipules separate early in the bud development). Thorns are straight to sickle-shaped, not spirally twisted (different from U. guianensis), very pungent and woody, from 8 to 20 mm long and 3 to 6 mm wide. When recently cut, the color of the inner bark can be whitish gray, yellowish brown, or dark red, with longitudinal fissures and persistent rhytidome. The internal part has a slightly dusty fibrous and laminar texture with a characteristic ferruginous dust and an extremely astringent taste. The terminal branches have a quadrangular section and yellowish green internal medulla.

Microscopic— The periderm with cork (phellem) is constituted by 6 to 8 rows of cells having walls evenly thickened, a compressed phellogen [note—The periderm and phellogen should be absent in the pharmacopeial article], and a phelloderm with 1 to 7 rows of sclereids. The secondary cortex with concentric rings of fibers are separated by rings of parenchyma; rings of fibers are frequently interrupted by radial rows of parenchyma cells (predominately 1 cell broad) or narrow medullary rays (few cells broad), forming rectangular bundles of fibers in a regular network; in longitudinal view the fibers appear with numerous conspicuous pits; calcium oxalate microcrystals (sand-like) are abundant in the parenchyma, but usually absent as large polyhedral crystals or in the form of styloids with bifurcated endings, the latter forms typically present in the parenchyma of U. guianensis; a brown substance is dispersed in parenchyma cells; starch is abundant, granules are solitary (circular in outline, up to 10 µm in diameter) or compound (2 to 3 components up to 15 µm in diameter).

A: Thin Layer Chromatographic Identification Test 201—

B: The chromatogram of the Test solution exhibits peaks for speciophylline, uncarine F, mitraphylline, isomitraphylline, pteropodine, and isopteropodine at retention times that correspond to those in the chromatogram of Standard solution 1, as obtained in the test for Content of pentacyclic oxindole alkaloids and limit of tetracyclic oxindoles.

Solution A— Prepare a filtered and degassed 10 mM pH 7.0 phosphate buffer by mixing 6 mL of 1 N sodium hydroxide, 10 mL of 1 M monobasic potassium phosphate, and sufficient water to make 1000 mL, and adjusting to a pH of 7.0 ± 0.1 by adding more of either solution.

Solution B— Use filtered and degassed acetonitrile.

Solution C— Prepare a filtered and degassed solution of methanol and glacial acetic acid (99:1).

Mobile phase— Use variable mixtures of Solution A, Solution B, and Solution C as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution 1— Dissolve an accurately weighed quantity of USP Powdered Cat's Claw Extract RS in methanol, shaking for 1 minute. Dilute with methanol to obtain a solution having a known concentration of about 0.5 mg of the labeled amount of total oxindole alkaloids per mL. Pass through a filter having a 0.45-µm or finer porosity.

Standard solution 2— Dissolve an accurately weighed quantity of USP Isopteropodine RS in methanol. Dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 0.1 mg per mL. Pass through a nylon filter having a 0.45-µm or finer porosity.

Test solution— Accurately weigh approximately 750 mg of ground Cat's Claw, and place in a 10-mL centrifuge tube. Sonicate with 2.5 mL of methanol for 10 minutes. Centrifuge, and transfer this solution to a 10-mL volumetric flask. Repeat the above extraction three additional times combining the extracts in the 10-mL volumetric flask, and dilute with methanol to volume. Transfer about 3 mL of the solution to a test tube containing 300 mg of polyamide powder, and shake for 1 minute. Pass through a nylon filter having a 0.45-µm or finer porosity, discarding the first part of the filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 245-nm detector and a 4.6-mm × 10-cm column that contains endcapped 3-µm packing L1. The flow rate is about 0.75 mL per minute. The chromatograph is programmed as follows. Inject into the chromatograph Standard solution 1 and Standard solution 2, and record the peak responses as directed for Procedure: the chromatogram obtained using Standard solution 1 is similar to the Reference Chromatogram provided with the USP Powdered Cat's Claw Extract RS; the tailing factor for the isopteropodine peak in Standard solution 2 is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of Standard solution 1, Standard solution 2, and the Test solution into the chromatograph, record the chromatograms, and measure the areas of the analyte peaks. Identify the retention times of the peaks corresponding to speciophylline, uncarine F, mitraphylline, isomitraphylline, pteropodine, and isopteropodine by comparison of the chromatogram of Standard solution 1 with the Reference Chromatogram provided with the lot of the USP Powdered Cat's Claw Extract RS used. Separately calculate the percentages of speciophylline, uncarine F, mitraphylline, isomitraphylline, rhynchophylline, isorhynchophylline, pteropodine, and isopteropodine, as isopteropodine, in the portion of Cat's Claw taken by the formula: in which C is the concentration, in mg per mL, of USP Isopteropodine RS in Standard solution 2; W is the weight, in g, of Cat's Claw taken to prepare the Test solution; rU is the peak response for each relevant alkaloid obtained from the Test solution; and rS is the peak response for isopteropodine obtained from Standard solution 2. Calculate the content of pentacyclic oxindole alkaloids by adding the percentages of speciophylline, uncarine F, mitraphylline, isomitraphylline, pteropodine, and isopteropodine. Calculate the content of tetracyclic oxindole alkaloids, as isopteropodine, by adding the individual percentages of rhynchophylline and isorhynchophylline: not more than 0.05 percent of tetracyclic oxindole alkaloids is found.