Bioorthogonal chemistry provides an exciting new strategy to visualize protein expression, track protein localization, measure protein activity, and identify protein interaction partners in living systems.[1] Two steps are typically involved in this approach: 1) the incorporation of a bioorthogonal group into a protein through either a biochemical pathway or semisynthesis; 2) a site-specific reaction between the protein that carries the bioorthogonal group and a cognate small-molecule probe. Although a plethora of methods have been developed to address the first step, such as non-sense suppression mutagenesis, [2] expressed protein ligation, [3] metabolic engineering, [4] and tagging-via-substrate, [5] only a small number of bioorthogonal reactions are known for the second step. These site-specific reactions include the acid-catalyzed nucleophilic addition of hydrazine to a ketone or aldehyde, [6] Staudinger ligation, [7] Cu I -catalyzed azide-alkyne 1,3-dipolar cycloaddition (click chemistry), [8] strain-promoted azide-alkyne 1,3-dipolar cycloaddition, [9] and the oxidative coupling of aniline.[10] To fully realize the potential of bioorthogonal chemistry in probing protein function, there is an urgent need for the discovery of additional bioorthogonal reactions with robust reaction attributes. Herein, we report a bioorthogonal, photoinducible 1,3-dipolar cycloaddition reaction that allows rapid and highly selective modification of proteins carrying a diaryl tetrazole group in biological media.Forty years ago, Huisgen and co-workers reported a photoactivated 1,3-dipolar cycloaddition reaction between 2,5-diphenyltetrazole and methyl crotonate.[11] A concerted reaction mechanism was proposed, whereby the diaryl tetrazole undergoes a facile cycloreversion reaction upon photoirradiation to release N 2 and generate in situ a nitrile imine dipole, which cyclizes spontaneously with an alkene dipolarophile to afford a pyrazoline cycloadduct (Scheme 1). The photolysis of diaryl tetrazoles was found to be extremely efficient upon UV irradiation at 290 nm, with quantum yields in the range 0.5-0.9.[12] Despite its robust mechanism, this photoactivated reaction has seen very few applications in the past four decades.[13]In our initial studies, we identified an extremely mild photoactivation procedure in the use of a hand-held UV lamp from UVP (UVM-57, 302 nm, 115 V, 0.16 amps). Under these mild conditions, the solvent compatibility, functional-group tolerance, regioselectivity, and yield of the photoactivated 1,3-dipolar cycloaddition reaction were excellent. [14] We then examined the reaction kinetics by incubating a tetrazole peptide with acrylamide in phosphate-buffered saline (PBS) at pH 7.5 under UV light (302 nm; see Figure S1 in the Supporting Information). We found that the photolysis of the tetrazole peptide to generate the nitrile imine intermediate was extremely rapid, with a first-order rate constant k 1 = 0.14 s À1 ; the subsequent cycloaddition with the dipolarophile acrylamide proceeded very efficiently, w...

We report the first application of a photoinduced 1,3-dipolar cycloaddition reaction to ‘staple’ a peptide dual inhibitor of the p53-Mdm2/Mdmx interactions. A series of stapled peptide inhibitors were efficiently synthesized and showed excellent dual inhibitory activity in ELISA assay. Furthermore, the positively charged, stapled peptides showed enhanced cellular uptake along with modest in vivo activity.

We report the first use of a photoinduced 1,3-dipolar cycloaddition reaction in "stapling" peptide side chains to reinforce a model peptide helical structure with moderate to excellent yields. The resulting pyrazoline "staplers" exhibit unique fluorescence useful in a cell permeability study.Peptide helices are frequent mediators of key protein-protein interactions that regulate many important biological processes such as stress response and apoptosis. 1 However, when peptide helices are taken out of protein context and placed into aqueous buffer in isolation, they usually adopt random coil conformations, leading to a drastic reduction in biological activity and thus diminished therapeutic potential. Among numerous strategies that aim to stabilize or mimic peptide helices, 2 the most straightforward, yet effective, strategy is sidechain cross-linking ("peptide stapling"). [3][4][5][6] In addition to structural reinforcement, peptide stapling usually leads to increased metabolic stability, improved membrane permeability, and potentially enhanced binding affinity to protein targets due to pre-organization.Since peptide stapling necessitates macrocyclization, an entropically unfavorable process, 7 very few reactions are known to date that give rise to good yields along with the reinforced structures. These include disulfide bond formation, 3 lactam formation, 4 ruthenium-catalyzed ring closing metathesis, 5 and copper-catalyzed azide-acetylene cycloaddition. 6 While these reactions have enabled the synthesis of stapled peptide helices, the development of additional stapling reactions with high yields and predictable structural effect is still highly desirable. Herein, we report the first synthesis of stapled peptide helices using a photoinduced nitrile imine-mediated intramolecular 1,3-dipolar cycloaddion reaction, and the subsequent structural, photophysical, and preliminary cellular uptake studies of the stapled peptides.We recently reported a photoactivated nitrile imine-mediated 1,3-dipolar cycloaddition as a new bioorthogonal reaction for protein labeling both in vitro and in vivo. 8 During these studies, we observed that the nitrile imine species, while reactive toward suitable alkenes, was exceedingly stable in the aqueous medium. To probe whether this unique reactivity profile can be harnessed to "staple" peptides, we appended an alkene and a tetrazole moiety, respectively, to peptide sidechains located at the i and i + 4 positions of Balaram's 3 10 -helix 9 (scheme in Table 1). We chose this peptide helix model because it has been studied previously by Grubbs and co-workers 5a in demonstrating ruthenium-catalyzed ring closing metathesis chemistry for † Electronic supplemental information ( NIH Public Access Author ManuscriptChem Commun (Camb). Author manuscript; available in PMC 2010 October 7. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript peptide stapling. We envisioned that upon photoirradiation, tetrazole would undergo the cycloreversion reaction to generate the ni...

Bioorthogonal chemistry provides an exciting new strategy to visualize protein expression, track protein localization, measure protein activity, and identify protein interaction partners in living systems.[1] Two steps are typically involved in this approach: 1) the incorporation of a bioorthogonal group into a protein through either a biochemical pathway or semisynthesis; 2) a site-specific reaction between the protein that carries the bioorthogonal group and a cognate small-molecule probe. Although a plethora of methods have been developed to address the first step, such as non-sense suppression mutagenesis, [2] expressed protein ligation, [3] metabolic engineering, [4] and tagging-via-substrate, [5] only a small number of bioorthogonal reactions are known for the second step. These site-specific reactions include the acid-catalyzed nucleophilic addition of hydrazine to a ketone or aldehyde, [6] Staudinger ligation, [7] Cu I -catalyzed azide-alkyne 1,3-dipolar cycloaddition (click chemistry), [8] strain-promoted azide-alkyne 1,3-dipolar cycloaddition, [9] and the oxidative coupling of aniline.[10] To fully realize the potential of bioorthogonal chemistry in probing protein function, there is an urgent need for the discovery of additional bioorthogonal reactions with robust reaction attributes. Herein, we report a bioorthogonal, photoinducible 1,3-dipolar cycloaddition reaction that allows rapid and highly selective modification of proteins carrying a diaryl tetrazole group in biological media.Forty years ago, Huisgen and co-workers reported a photoactivated 1,3-dipolar cycloaddition reaction between 2,5-diphenyltetrazole and methyl crotonate.[11] A concerted reaction mechanism was proposed, whereby the diaryl tetrazole undergoes a facile cycloreversion reaction upon photoirradiation to release N 2 and generate in situ a nitrile imine dipole, which cyclizes spontaneously with an alkene dipolarophile to afford a pyrazoline cycloadduct (Scheme 1). The photolysis of diaryl tetrazoles was found to be extremely efficient upon UV irradiation at 290 nm, with quantum yields in the range 0.5-0.9.[12] Despite its robust mechanism, this photoactivated reaction has seen very few applications in the past four decades.[13]In our initial studies, we identified an extremely mild photoactivation procedure in the use of a hand-held UV lamp from UVP (UVM-57, 302 nm, 115 V, 0.16 amps). Under these mild conditions, the solvent compatibility, functional-group tolerance, regioselectivity, and yield of the photoactivated 1,3-dipolar cycloaddition reaction were excellent. [14] We then examined the reaction kinetics by incubating a tetrazole peptide with acrylamide in phosphate-buffered saline (PBS) at pH 7.5 under UV light (302 nm; see Figure S1 in the Supporting Information). We found that the photolysis of the tetrazole peptide to generate the nitrile imine intermediate was extremely rapid, with a first-order rate constant k 1 = 0.14 s À1 ; the subsequent cycloaddition with the dipolarophile acrylamide proceeded very efficiently, w...

Objective. To determine whether there is a difference in pass rates on the North American Pharmacist Licensure Examination (NAPLEX) between students who did and did not require remediation for deficient course grades. Methods. Student-specific data were collected regarding course grade deficiencies and completion of a comprehensive examination or course for remediation. Student-specific first-time NAPLEX performance data for the graduating classes of 2008, 2009, and 2011were provided by the National Association of Boards of Pharmacy (NABP). Results. A significant difference was found in first-time NAPLEX mean pass rates between students who did not need to undergo remediation versus those who did ( 97% vs 70%). Conclusion. Students requiring remediation for deficient course grades had a lower pass rate on the NAPLEX compared with those who did not require remediation. The difference can be attributed to several factors and therefore further study is needed.

We report a chemical lipidation model for the study of protein lipidations in vitro and in live mammalian cells based on a bioorthogonal, photoinduced tetrazole-alkene cycloaddition reaction.Protein lipidation-the covalent attachment of lipid anchors to a protein-regulates many cellular processes by controlling subcellular protein localization. 1 A prominent example is N-Ras, which controls cell growth, differentiation, and apoptosis by acting as a molecular switch in the signal transduction pathway, cycling between the inactive GDP-bound form and the active GTP-bound form. 2 As a prerequisite for its biological activity, N-Ras requires two sequential lipidations -a palmitoylation at Cys-181 and a farnesylation at Cys-186-in order to partition into proper compartments (Fig. 1a). 3 While the affinities of various lipid anchors toward membrane structures have been studied in vitro using the lipid bilayer model, 4 the dynamics of spatiotemporal segregation of proteins upon lipidation in vivo remains less well understood. 5 To probe the effect of lipidation on protein localization dynamics in vivo, two strategies have been successfully developed. One involved the fusion of fluorescent proteins to the target protein to facilitate its monitoring by confocal fluorescent microscopy. 6 Another involved the microinjection of the dye-labeled, semisynthesized proteins with the predetermined lipidation patterns into living cells followed by examination of its subcellular localizations by fluorescent microscopy. 7 While these two approaches have elucidated the effect of lipidation on protein localization, the spatiotemporal resolution of intracellular trafficking upon lipidation was limited. We have recently reported a photoinduced tetrazolealkene cycloaddition reaction for selective functionalization of either tetrazole or alkenecontaining proteins both in vitro and in vivo. 8 We envisioned that this photoinduced bioorthogonal reaction may provide a chemical strategy for probing protein lipidation in live cells with an improved spatiotemporal resolution. A two-step procedure will be employed in this approach; the photoreactive tetrazoles are first incorporated at the target lipidation sites, which then react with exogenous lipid dipolarophiles to form the lipidated products via the photoinduced cycloaddition reaction ( Correspondence to: Qing Lin, qinglin@buffalo.edu. Since successive lipidations are typically required for stable membrane association, we decided to examine the effect of lipid numbers by preparing two semi-synthetic EGFP proteins carrying varying number of photoreactive tetrazole moieties using the inteinmediated protein ligation strategy (Scheme 1). Thus, two short peptides containing either one (Tet 1) or two (Tet 2) tetrazole sidechains were prepared via solid-phase peptide synthesis. 10 In parallel, we cloned EGFP(1-239) into the ligation vector, pTXB1, and overexpressed EGFP-intein-CBD in E. coli. The ligation products, EGFP-Tet 3 and 4, were obtained by incubating the immobilized fusion prot...

Aerospace simulations can model worlds, such as the Earth, with differing levels of fidelity. The simulation may represent the world as a plane, a sphere, an ellipsoid, or a highorder closed surface. The world may or may not rotate. The user may select lower fidelity models based on computational limits, a need for simplified analysis, or comparison to other data. However, the user will also wish to retain a close semblance of behavior to the real world. The effects of gravity on objects are an important component of modeling real-world behavior. Engineers generally equate the term gravity with the observed free-fall acceleration. However, free-fall acceleration is not equal to all observers. To observers on the surface of a rotating world, free-fall acceleration is the sum of gravitational attraction and the centrifugal acceleration due to the world's rotation. On the other hand, free-fall acceleration equals gravitational attraction to an observer in inertial space. Surface-observed simulations (e.g. aircraft), which use non-rotating world models, may choose to model observed free fall acceleration as the "gravity" term; such a model actually combines gravitational attraction with centrifugal acceleration due to the Earth's rotation. However, this modeling choice invites confusion as one evolves the simulation to higher fidelity world models or adds inertial observers. Care must be taken to model gravity in concert with the world model to avoid denigrating the fidelity of modeling observed free fall. The paper will go into greater depth on gravity modeling and the physical disparities and synergies that arise when coupling specific gravity models with world models.

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