Urea, as substrate

Bovine serum albumin (BSA) and cyclic AMP (cAMP) are determined by a competitive binding enzyme immunoassay (315). With urease as label, an ammonia gas-sensing electrode is used to measure the amount of urease-labeled antigen bound to a double-antibody solid phase by continuously measuring the rate of ammonia produced from urea as substrate. The method yields accurate and sensitive assays for proteins (BSA less than 10 ng/mL) and antigens (cAMP less than 10 nM), with fairly good selectivity over cGMP, AMP, and GMP. 

Insertion into Carbon-Heteroatom tr-Bonds. Shirakawa et al. reported the first example of insertion of arynes into a C—N bond. Using ureas as substrates a wide variety of 1-amino-2-(aminocarbonyl)arenes 86, including 1,4-benzodiazepine and 1,5-benzodiazocme derivatives, can be prepared (Scheme 12.45) [76]. Related to this work, Larock et al. developed the intermolecnlar C—N addition of amides across the aryne triple bond, providing access to (6>-anilino)triflnoroaceto-phenones 87. The presence of the CF snbstituent resulted to be crucial for the insotion process, which were limited to secondary snbstrates (Scheme 12.45) [77]. 

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