Ruthenium-induced allylcarbamate cleavage in living cells.

Organometallics are increasingly gaining attention as tools in chemical biology owing to their distinguished physicochemical properties, reactivities, and three-dimensional structures. Along these lines, the exceptional ability of organometallic compounds to catalyze a wide variety of chemical transformations has not yet been sufficiently exploited for chemical biology, but could yield bioactive molecules with novel properties. For example, such catalysts could eventually be used to amplify signals by turning over a substrate multiple times, catalytically label or deactivate target biomolecules, or release prodrugs and all this in a cellular environment. However, designing catalysts which work under physiological conditions is a significant challenge owing to the combined presence of air, water, and a plethora of cellular components such as millimolar concentrations of thiols, which are prone to poison organometallic catalysts, especially under protic and aerobic conditions. With respect to this new aspect of bioorganometallic chemistry, we herein disclose a ruthenium-catalyzed release of amines from their allylcarbamates that tolerates the combination of water, air, and thiols, and we demonstrate the utility of this cleavage reaction in living mammalian cells. In the course of screening several organometallic catalysts for a variety of reactions, we found that the complex [Cp*Ru(cod)Cl] (Cp*= pentamethylcyclopentadienyl, cod= 1,5-cyclooctadiene; 1) catalyzes the cleavage of allylcarbamates 2 to their respective amines 3 in the presence of an excess of thiophenol in an open flask experiment, tolerating water and air (Scheme 1). 12] For example, the reaction of pmethylaniline allylcarbamate 2a (200 mm) with 5 equivalents of thiophenol in the presence of 10 mol% ruthenium catalyst 1, carried out in MeOH/H2O (95:5) under air and overnight at room temperature, provides p-methylaniline in 86% yield if isolated as the tert-butoxycarbonyl (Boc)-protected amine, and 89% yield according to GC analysis (Table 1, entry 1). This deprotection is quite general as it works under the same conditions with high yields also for allylcarbamates of an electron-acceptor-substituted aniline (2b, 85% yield) and a primary (2c, 94%, isolated as the Boc-protected amine), as well as a secondary amine (2d, 87% yield; Scheme 1). The influence of air, water, and aliphatic thiols on the GCdetermined yields of this ruthenium-catalyzed cleavage is shown for substrate 2a in Table 1. Accordingly, yields are not significantly affected by air and water (Table 1, entries 1–3). In contrast, omitting thiophenol prevents the carbamate cleavage completely in the presence of water and air (Table 1, entry 4). Most importantly for cellular applications, the cleavage reaction can be performed in the presence of aliphatic thiols, such as benzeneethanethiol, with virtually no influence on the yield of the reaction (93%; Table 1, entry 5). However, if performed at room temperature, the aromatic thiol is necessary because substitution for an aliphatic thiol leads to a significant reduction in yield (34%; Table 1, entry 6). Interestingly, increasing the temperature to 37 8C provides the released amine with an improved yield of 67% by using the aliphatic thiol benzeneethanethiol as the only nucleophile. To evaluate the carbamate cleavage under conditions that more closely resemble a physiological environment, the bis[*] C. Streu, Prof. E. Meggers Department of Chemistry University of Pennsylvania 231 South 34th Street, Philadelphia, PA 19104 (USA) Fax: (+1)215-746-0348 E-mail: meggers@sas.upenn.edu Homepage: http://www.sas.upenn.edu/~meggers/