ABSTRACT
Microwave heating was used to prepare eta5-rhenium carborane complexes in aqueous reaction media. For carboranes bearing sterically demanding substituents, isomerization of the cage from 3,1,2 to 2,1,8 derivatives occurred concomitantly with complexation. Microwave heating was equally effective at the tracer level using technetium-99m, affording access to a new class of synthons for designing novel molecular imaging agents.
Subject(s)
Carbon/chemistry , Chemistry/methods , Microwaves , Organotechnetium Compounds/chemical synthesis , Radiopharmaceuticals/chemical synthesis , Rhenium/chemistry , Technetium/chemistry , Metals/chemistry , Models, Chemical , Molecular Conformation , Organotechnetium Compounds/chemistry , Radiopharmaceuticals/chemistryABSTRACT
A method for the preparation of eta5-metallocarborane complexes of technetium-99m in water was developed. The key to the procedure is the use of aqueous sodium or potassium fluoride, which prevents premature degradation of the Tc(I) starting material used to prepare the carborane complexes. Solid-phase extraction was used to purify Tc-metallocarboranes derived from both ortho and meta isomers, which were isolated in good to excellent yields in high radiochemical purities. In conjunction with these studies, a series of fluoride-based "kits" were developed to produce the key precursor [99mTc(CO)3(H2O)3]+ in the absence of any other stabilizing ligand. Using this approach, [99mTc(CO)3(H2O)3]+ could be prepared directly from 99mTcO4- under a range of pH values, including neutral pH, which affords the opportunity to develop one-pot labeling procedures for base-sensitive targeting vectors.
Subject(s)
Boron Compounds/chemical synthesis , Fluorides/chemistry , Organometallic Compounds/chemical synthesis , Technetium/chemistry , Boron Compounds/chemistry , Chromatography, High Pressure Liquid , Hydrogen-Ion Concentration , Molecular Conformation , Organometallic Compounds/chemistry , Water/chemistryABSTRACT
A series of metallocarboranes of the types rac-[M(CO)3(eta(5)-7-R-7,8-C2B9H11)]-, rac-[M(CO)3(eta(5)-7-R-8-R'-7,8-C2B9H11)]-, and rac-[M(CO)3(eta(5)-7-R-7,9-C2B9H11)]- (M=Re) were prepared by reacting [NEt4]2[Re(CO)3Br3] or [Re(CO)3(OH2)3]Br with the corresponding carboranes in the presence of aqueous solutions of either alkali metal or tetraalkylammonium fluoride salts. Carborane derivatives that were investigated included those containing pyridine, amino, carboxylic acid, carbohydrate, and aryl substituents. During the course of the research, it was discovered that Re metallocarboranes can be prepared directly from the respective closo-clusters under similar reaction conditions used with nido-carboranes. Reaction yields ranged from modest to excellent depending on the carborane isomer and the nature of the cage substituent(s). A crystal structure of an amine-substituted Re metallocarborane was obtained where the complex crystallized in the orthorhombic space group P2(1)2(1)2(1) with a=8.982(2) A, b=11.563(3) A, c=16.811(4) A, alpha=beta=gamma=90 degrees, V=1746.1(7) A3, Z=4, and R1=0.0684.