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p-Hydroxyphenacyl, a new photoactive, aqueous soluble protecting group is proposed as a second generation α- keto “cage” reagent, a phototrigger for the efficient, rapid release of bioactive phosphates, e.g., inorganic phosphate (Pi) and ATP (Givens, R. S.; Park, C.-H. Tetrahedron Lett. 1996, 37, 6259−6262). p-Hydroxyphenacyl esters 6c and 7 trigger the release of Pi and ATP when irradiated at wavelengths between 300−350 nm also yielding p-hydroxyphenylacetic acid (8) from the rearrangement of the intermediate α-keto carbocation or its equivalent. In contrast, unsubstituted and m-substituted phenacyl esters yield only photoreduction and radical coupling products and none of the rearrangement product. Quantum efficiencies of 0.38 ± 0.04 were measured for the disappearance of the p-hydroxyphenacyl phosphate esters 6c and 7; the appearance efficiencies for 8 and ATP were 0.30 ± 0.03. Rates of release of ∼107 s-1 or better are observed for these esters with only minor variations in efficiencies and rate constants between these two examples of the p-hydroxyphenacyl phototrigger. Just as was found for the desyl “cage” series reported earlier (Givens, R. S.; Athey, P. S.; Kueper, L. W., III; Matuszewski, B.; Xue, J.-y.; Fister, T. J. Am. Chem. Soc. 1993, 115, 6001−6010), the p-hydroxyphenacyl derivatives react via their triplet states. Amino substituents, i.e., p-amino-, p-acetamido-, and p-(carbomethoxyamino)phenacyl phosphates 6f−h, were also investigated, but these analogues proved to be inferior as phototriggers when compared with p-hydroxyphenacyl.

On the basis of the Isolndole formation mechanism In the o-phthalaldehyde/2-mercaptoethanol (OPA/2-ME) derivatization of primary amines and the structure-stability relationships for Isolndoles, an Improved fluorogenic reagent, naphthalene-2,3-dlcarboxaldehyde (NDA) In the presence of cyanide ion (CN ), has been developed. Reaction of NDA/ CN' with primary amines In aqueous media results In the formation of -substKuted 1-cyanobenz[/]lsoindole (CBI) derivatives which have significantly Improved stability compared to the corresponding OPA/2-ME derivatives (for glycine greater than 50-fold Improvement was realized) and have high quantum efficiencies for fluorescence ( , = 0.54 In 60% aqueous acetonitrile for the CBI--propylamine derivative) In solvent systems commonly used In liquid chromatography. Parameters In the NDA/CN' derivatization of alanine are defined (l.e., pH and the reagent component concentrations) and used In the development of a labeling procedure for amino acid mixtures. Gradient elution fractionation of 18 CBI-amino acid derivatives was accomplished In 60 min and permitted detection limits of less than 200 fmol Injected (excitation 246 nm) or 3 pmol Injected (excitation 420 nm). The utility of the reagent In assaying amino acid mixtures resulting from the enzymatic hydrolysis of the peptides Met-enkephalln and glucagon Is demonstrated.

Most applications of photoremovable protecting groups have used o-nitrobenzyl compounds and their (often commercially available) derivatives that, however, have several disadvantages. The focus of this review is on applications of the more recently developed title compounds, which are especially well suited for time-resolved biochemical and physiological investigations, because they release the caged substrates in high yield within a few nanoseconds or less. Together, these two chromophores cover the action spectrum for photorelease from >700 nm to 250 nm.

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p-Hydroxyphenacyl is an effective photoremovable protecting group, not least due to the fast release of its substrates, accompanied by a photo-Favorskii rearrangement of compounds 1 to p-hydroxyphenylacetic acid (2) that is transparent down to 300 nm. First used for the release of ATP from 1 (X = ATP) a decade ago, 1 the reaction has been employed in a variety of fields as diverse as neurobiology, 2 enzyme catalysis, 3 and biochemistry. 4 The nature and timing of the bond-making and bond-breaking events have not been fully elucidated despite extensive experimental and theoretical efforts by our group 5 and others. 6,7 We now report observation of the primary photoproduct, the triplet biradical 3 3, and of a new side product, p-hydroxybenzyl alcohol (6), that is formed by decarbonylation of the putative spirodione intermediate 4 at moderate water concentrations (Scheme 1). Solvent kinetic isotope effect (SKIE) studies by nanosecond laser flash photolysis (LFP) provide significant information on the role of water in the photo-Favorskii rearrangement of p-hydroxyphenacyl diethyl phosphate 1a to p-hydroxyphenylacetic acid (2). Anderson and Reese first reported the intriguing photoreaction 1(X = Cl) → 2 + HCl and suggested that the skeletal rearrangement may proceed via a spirodione intermediate 4, 8 which has yet to be detected. Intersystem crossing (ISC) of diethyl phosphate 1a is very fast, k ISC = 4 × 10 11 s −1 , 5 and we have established that the rearrangement proceeds from the triplet state, T 1. 1,4b,5 This was confirmed by Phillips et al. 7a-c Hydroxylic solvents play a major role in the rearrangement. The lifetime of T 1 decreases from several μs in degassed, dry CH 3 CN to about 0.4 ns in aqueous CH 3 CN (50% by vol). 5,7c,d The lifetime of T 1 of 1a is further reduced to 100 ± 10 ps in 87% aqueous CH 3 CN (Figure 1) and to 63 ± 10 ps in wholly aqueous solution. This was the key to revealing that the decay of T 1 left weak absorptions at 445, 420, and 330 nm, which decayed with a somewhat longer lifetime of ca. 0.6 ns. Pump-probe spectra obtained with other derivatives of 1 with good leaving groups (1b,c: X = tosylate, mesylate) also displayed the transient species possessing

Type III secretion (TTS) is an essential virulence function forShigella flexneri that delivers effector proteins that are responsible for bacterial invasion of intestinal epithelial cells. The Shigella TTS apparatus (TTSA) consists of a basal body that spans the bacterial inner and outer membranes and a needle exposed at the pathogen surface. At the distal end of the needle is a "tip complex" composed of invasion plasmid antigen D (IpaD). IpaD not only regulates TTS, but is required for the recruitment and stable association of the translocator protein IpaB at the TTSA needle tip in the presence of deoxycholate or other bile salts. This phenomenon is not accompanied by induction of TTS or the recruitment of IpaC to the Shigella surface. We now show that IpaD specifically binds fluorescein-labeled deoxycholate and, based on energy transfer measurements and docking simulations, this interaction appears to occur where the N-terminal domain of IpaD meets its central coiled-coil, a region that may also be involved in needle-tip interactions. TTS is initiated as a series of distinct steps and that small molecules present in the bacterial milieu are capable of inducing the first step of TSS through interactions with the needle tip protein IpaD. Furthermore, the amino acids proposed to be important for deoxycholate binding by IpaD appear to have significant roles in regulating tip complex composition and pathogen entry into host cells.Shigella flexneri is the etiologic agent of shigellosis, a potentially life-threatening bacillary dysentery in humans. Although shigellosis is typically considered a disease of the developing world, it is an underreported problem in industrialized nations where it is an infectious agent in child daycare centers, nursing homes, and in any situation where sanitation procedures become compromised (1). Shigellosis is spread by the fecal-oral route with larger outbreaks linked to contaminated water, which makes it a serious public health problem anywhere treatment regimens are inadequate. Following ingestion, Shigella travels to the colon where it crosses M cells and kills macrophages to gain access to the basal side of the colonic epithelium. S. flexneri then promotes its own uptake into epithelial cells by inducing membrane ruffling at the site of pathogen contact.Shigella invasiveness is the product of a 31-kb segment on its large virulence plasmid, which encodes the components of a type III secretion system (TTSS). 4 The Shigella TTSS is used to subvert the normal host cell mechanisms that control the actin cytoskeleton to promote invasion (2, 3). Within this genetic region, the mxi/spa operons encode the type III secretion apparatus (TTSA) and the ipa/ipg operon encodes the type III secreted protein effectors/translocators, IpaA-D, and IpgC, the cytoplasmic chaperone for IpaB and IpaC (4). The TTSA is a nanomachine that provides a conduit for secretion from the bacterial cytoplasm to the membrane and cytoplasm of target cells. It is composed of two main parts: an external needle that allow...

In our search for a more versatile protecting group that would exhibit fast release rates for peptides, we have designed and developed the p-hydroxyphenacyl (pHP) group as a new photoremovable protecting group. We report the application of this protecting group for the dipeptide Ala-Ala (1) and for the nonapeptide bradykinin (2), two representative peptides that demonstrate C-terminus "caging" and photorelease. The synthesis of these p-hydroxyphenacyl esters was accomplished in good yields by DBU-catalyzed displacement of bromide from p-hydroxyphenacyl bromide. As in the case of caged γ-amino acids 11 (pHP glu) and 12 (pHP GABA) and caged nucleotide 17 (pHP ATP) reported earlier, 1,2 irradiations of the p-hydroxyphenacyl esters of 1 and 2 actuate the release of the peptides with rate constants that are consistently greater than 10 8 s -1 and appearance efficiencies (Φ app ) that range from 0.1 to 0.3. Release of the substrate is accompanied by a deep-seated rearrangement of the protecting group into the near-UV silent p-hydroxyphenylacetic acid (6). Quenching studies of pHP Ala-Ala (7) with either sodium 2-naphthalenesulfonate or potassium sorbate gave good Stern-Volmer kinetics yielding a rate constant for release of 1.82 × 10 8 s -1 . Quenching of the phosphorescence emission from pHP Ala-Ala (7, E T ) 70.1 kcal/mol) and pHP GABA (12, E T ) 68.9 kcal/mol) were also observed. The biological efficacy of bradykinin released from pHP bradykinin (9) was examined on single rat sensory neurons grown in tissue culture. A single 337 nm flash (<1 ns) released sufficient bradykinin from the p-hydroxyphenacyl protected nonapeptide to activate cell-surface bradykinin receptors as indicated by a rapid increase in the intracellular calcium concentration. A selective antagonist of type 2 bradykinin receptors blocked the biological response. From these results, it is apparent that flash photolysis of p-hydroxyphenacyl protected peptides provides a powerful tool for the rapid and localized activation of biological receptors.