A traceless linker for aliphatic amines that rapidly and quantitatively fragments after reduction

Reduction sensitive linkers (RSLs) have the potential to transform the field of drug delivery due to their ease of use and selective cleavage in intracellular environments. However, despite their compelling attributes, developing reduction sensitive self-immolative linkers for aliphatic amines has been challenging due to their poor leaving group ability and high pK_a values. Here a traceless self-immolative linker composed of a dithiol-ethyl carbonate connected to a benzyl carbamate (DEC) is presented, which can modify aliphatic amines and release them rapidly and quantitatively after disulfide reduction. DEC was able to reversibly modify the lysine residues on CRISPR–Cas9 with either PEG, the cell penetrating peptide Arg₁₀, or donor DNA, and generated Cas9 conjugates with significantly improved biological properties. In particular, Cas9–DEC–PEG was able to diffuse through brain tissue significantly better than unmodified Cas9, making it a more suitable candidate for genome editing in animals. Furthermore, conjugation of Arg₁₀ to Cas9 with DEC was able to generate a self-delivering Cas9 RNP that could edit cells without transfection reagents. Finally, conjugation of donor DNA to Cas9 with DEC increased the homology directed DNA repair (HDR) rate of the Cas9 RNP by 50% in HEK 293T cell line. We anticipate that DEC will have numerous applications in biotechnology, given the ubiquitous presence of aliphatic amines on small molecule and protein therapeutics.

Reduction sensitive linkers (RSLs) have the potential to transform the field of drug delivery due to their ease of use and selective cleavage in intracellular environments.     

Synthesis and characterization of amino-terminated telechelic polybutadiene

Butadiene was polymerized with water-soluble 4,4′-azobis(amidinopropane)dihydrochloride initiator in an ethanol-water medium at 60°C. Important variables, such as the initiator concentration, monomer concentration, solvency, and polymerization time and temperature were studied. ¹³C-NMR studies showed that no observable chain transfer to ethanol occurred during the polymerization. The conversion of monomer to polymer was significantly increased while maintaining a relatively narrow molecular weight distribution by intermittent feed of the initiator. The amidino end-groups of the polymer were transformed into amino groups by reduction using lithium aluminum hydride in THF, so that amine-terminated polybutadiene was obtained. The amino functionality of the polybutadiene was determined by titration to be 2.0. © 1995 John Wiley & Sons, Inc.     

Autoprotolysis constants and standardization of the glass electrode in acetonitrile-water mixtures. Effect of solvent composition

Standard e.m.f.s for the cell GE/HCl/AgCl/Ag/Pt (GE=glass electrode) in acetonitrile-water mixtures containing 0–70% (w/w) of acetonitrile were obtained. Values of the autoprotolysis constant, K_ap, of these mixed solvents were also determined from e.m.f. measurements of the cell GE/KCl + KS/AgCl/Ag/Pt. The influence of variations in the solvent composition on pK_ap values was evaluated. Over the whole of the composition range studied the pK_ap values were linearly correlated with the mole fraction of acetonitrile and with the reciprocal of the relative permittivity of solvent mixtures. Linear relationships were also obtained for pK_ap values vs. the Kamlet-Taft π^★ polarizability/dipolarity parameter in the range 0–50% (w/w).     

δ-Nitroalkanols as precursors for the one-pot synthesis of substituted tetrahydrofurans

DBU catalyses the one-pot Michael addition of nitroalkanes to 1,4-dienone derivatives, elimination of nitrous acid, then intramolecular conjugate addition-ring closure to allow the direct formation of a variety of tetrahydrofurans.     

Liquid chromatography-mass spectrometry approach for the characterization and purification of crude synthetic peptide hormones

In this study, conditions for the optimal separation by LC-UV and characterisation by LC-ES-MS of crude mixtures generated during SPPS of several peptide hormones are compiled. The linear solvation energy relationship (LSER) methodology has been used to predict the retention of the target peptides and their side products and then to develop a separation LC methodology with applicability on both the analytical and preparative scale. Identification of these side products by LC-ES-MS analysis has been made on the basis of their calculated molecular masses. This method may be regarded as a key tool for the optimisation of the synthetic procedures and for complying with regulatory agencies' requirements before commercialisation of a safe and effective peptide-based pharmaceutical drug.Awarded a prize as outstanding poster on the occasion of Jornadas de Análisis Instrumental (JAI), November 26 to 29, 2002, Barcelona, Spain     

Assignment of reference pH-values to primary standard buffer solutions for standardization of potentiometric sensors in acetonitrile-water mixtures

Standard pH-values pH(PS) for seven primary standard buffer solutions in 0, 10, 30, 40, 50, 70 and 100% (w/w) acetonitrile-water mixed solvents at 298.15 K were determined according to the criteria recently endorsed by IUPAC. The preferential solvation of the ions in acetonitrile-water mixtures was studied in order to clarify the acid-base behaviour of the solutes in such mixtures. The influence of variation in the solvent composition on pH(PS) values was considered with a view to obtaining correlations that can be used to determine the pH(PS) values in any acetonitrile-water mixture up to 70% (w/w) acetonitrile. The pH(PS) values were then correlated with the weight and volume percentages and molar fraction of acetonitrile and with the Kamlet-Taft, pi(*), alpha and beta solvatochromic parameters of the acetonitrile-water mixtures. The equations obtained permit the standardization of potentiometric sensors in these mixtures.     

Rapid on-membrane proteolytic cleavage for Edman sequencing and mass spectrometric identification of proteins

A method for the rapid limited enzymatic cleavage of PVDF membrane-immobilized proteins is described. This method allows the fast characterization of PVDF blotted proteins by peptide mass fingerprinting (Henzel, W. J., Billeci, T. M., Stults, J. T., Wong, S. C., Grimley, C., Wantanabe, C., Proc. Natl. Acad. Sci. USA 1993, 90, 5011-5015), LC-MS/MS, or N-terminal sequencing and has been demonstrated on a range of proteins using a full complement of proteolytic enzymes. This technique allows the generation of proteolytic fragments between 5 and 60 min (depending on the enzyme employed), which is significantly faster than previously reported on-membrane digestion methods. To date, this on-membrane rapid digestion protocol has aided in the identification and confirmation of mutation sites in over 200 recombinant proteins.     

Effect of the solvent on the equilibria of acid-base indicators in aprotic and amphiprotic solvents

The dissociation constants of a series of indicators inN,N-dimethylformamide medium have been determined, and compared with those for the indicators in other aprotic solvents (dimethylsulphoxide and acetonitrile) and in some amphiprotic solvents (water, methanol, ethanol, propan-2-ol and tertbutanol). The effect of the solvent characteristics on the pK values have been evaluated, and the pK + p _ws ^t (H⁺) values shown to be linearly correlated with the Dimroth and ReichardtE _T ^N and acceptor number solvatochromic parameters.     

Protonation equilibria of quinolone antibacterials in acetonitrile-water mobile phases used in LC

Ionization constants of nine quinolone antibacterials in acetonitrile-water mixtures containing 0, 5.5, 10, 16.3, 25, 30, 40, 50 and 70% (w/w) acetonitrile were obtained and assignment of these pK values to the several potentially ionizable functional groups was made. The variation of the pK values obtained over the whole composition range studied can be explained by consideration of the preferential solvation of electrolytes in acetonitrile-water mixtures. In order to obtain pK values in any of the unlimited number of possible binary solvent acetonitrile-water mixtures, relationships between pK values and different bulk properties (such as dielectric constant) were examined. The linear solvation energy relationships method, LSER, was applied to study the correlation of pK values with the solvatochromic parameters of acetonitrile-water mixtures. The equations obtained allow calculation of the pK values of the quinolone antimicrobials in any acetonitrile-water mixtures up to 70% (w/w) and thus permit the knowledge of the acid-base behaviour of these important antimicrobials in the widely used acetonitrile-water media.     

On the rate of convergence to the normal law for solutions of the Burgers equation with singular initial data

We study the scaling limit of random fields which are the solutions of a nonlinear partial differential equation known as the Burgers equation, under stochastic initial condition. These are assumed to be a Gaussian process with long-range dependence. We present some results on the rate of convergence to the normal law.