Solid-phase N-terminus PEGylation of recombinant human fibroblast growth factor 2 on heparin-sepharose column

Recombinant fibroblast growth factor-2 (FGF-2) has been extensively studied and used in several clinical applications including wound healing, bone regeneration, and neuroprotection. Poly(ethylene glycol) (PEG) modification of recombinant human FGF-2 (rhFGF-2) in solution phase has been studied to increase the in vivo biostabilities and therapeutic potency. However, the solution-phase strategy is not site-controlled and the products are often not homogeneous due to the generation of multi-PEGylated proteins. In order to increase mono-PEGylated rhFGF-2 level, a novel solid-phase strategy for rhFGF-2 PEGylation is developed. RhFGF-2 proteins were loaded onto a heparin-sepharose column and the PEGylaton reaction was carried out at the N-terminus by PEG20 kDa butyraldehyde through reductive alkylation. The PEGylated rhFGF-2 was purified to near homogeneity by SP sepharose anion-exchange chromatography and the purity was more than 95% with a yield of mono-PEGylated rhFGF-2 of 58.3%, as confirmed by N-terminal sequencing and MALDI-TOF mass spectrometry. In vitro biophysical and biochemical measurements demonstrated that PEGylated rhFGF-2 has an unchanged secondary structure, receptor binding activity, cell proliferation, and MAP kinase stimulating activity, and an improved bio- and thermal stability. Animal assay showed that PEGylated rhFGF-2 has an increased half-life and reduced immunogenicity. Compared to conventional solution-phase PEGylation, the solid-phase PEGylation is advantageous in reaction time, production of mono-PEGylated protein, and improvement of biochemical and biological activity.     

Optimization of octreotide PEGylation by monitoring with fast reversed-phase high-performance liquid chromatography

The purpose of this study was to develop a fast reversed-phase high-performance liquid chromatography (HPLC) method for monitoring the octreotide PEGylation reaction in order to find optimal conditions for the production of the desired mono-PEGylated octreotide. The fast HPLC method could separate the positional isomers of two mono-PEGylated octreotides, di-PEGylated octreotide, and unmodified octreotide within 4.5 min. The PEGylation pattern was monitored at various pH conditions and molar ratios of reactants to allow optimization of the PEGylation reaction conditions for the production of N-terminally mono-PEGylated octreotide.     

Synthesis of Mono-PEGylated Growth Hormone Releasing Peptide-2 and Investigation of its Biological Activity

The purpose of this study was to investigate an efficient synthetic route to the mono-PEGylated growth hormone releasing peptide-2 (GHRP-2) and its biological activity in vivo. The commercially available key PEGylating reagent, mPEG-NHS ester, was successfully utilized to the synthesis of mono-PEGylated GHRP-2, during which the PEGylation profiles of GHRP-2 were monitored by high-performance liquid chromatography (HPLC). The product was purified by cation exchange chromatography, and its biological activity was conducted in rats. The desired mono-PEGylated GHRP-2 as the major product was readily obtained in anhydrous aprotic solvent, such as dimethyl formamide (DMF) and dimethylsulfoxide (DMSO), when the molar ratio of mPEG-NHS ester to GHRP-2 was fixed to be 0.8:1. The products were characterized by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. The evaluation of the biological activity for the products showed that the mono-PEGylated GHRP-2 gave a more stable activity than GHRP-2, suggesting that PEGylation led to the increase in the half-life of GHRP-2 in plasma without greatly impairing the biological activity. PEGylation of the GHRP-2 is a good choice for the development of the GHRP-2 applications.KEY WORDS: growth hormone, growth hormone releasing peptide-2, mono-PEGylated GHRP-2, mPEG-NHS, PEGylation     

Cardiovascular effects of a PEGylated apelin

Several studies have documented cardiovascular effects of apelin, including enhanced inotropy and vasodilation. However, these cardiovascular effects are short lived due to the predicted short circulating half-life of the apelin peptide. To address this limitation of apelin, we pursued N-terminal PEGylation of apelin and examined the cardiovascular effects of the PEGylated apelin. A 40 kDa PEG conjugated apelin-36 (PEG–apelin-36) was successfully produced with N-terminal conjugation, high purity (>98%) and minimum reduction of APJ receptor binding affinity. Using an adenylate cyclase inhibition assay, comparable in vitro bioactivity was observed between the PEG–apelin-36 and unmodified apelin-36. In vivo evaluation of the PEG–apelin-36 was performed in normal rats and rats with myocardial infarction (MI). Cardiac function was assessed via echocardiography before, during a 20 min IV infusion and up to 100 min post peptide infusion. Similar increases in cardiac ejection fraction (EF) were observed during the infusion of PEG–apelin-36 and apelin-36 in normal rats. However, animals that received PEG–apelin-36 maintained significantly increased EF over the 100 min post infusion monitoring period compared to the animals that received unmodified apelin-36. Interestingly, EF increases observed with PEG–apelin-36 and apelin-36 were greater in the MI rats. PEG–apelin-36 had a prolonged circulating life compared to apelin-36 in rats. There were no changes in aortic blood pressure when PEG–apelin-36 or apelin-36 was administered. To our knowledge this is the first report of apelin PEGylation and documentation of its cardiovascular effects.     

Structural identification and biological activity of positional isomers of long-acting and mono-PEGylated recombinant human granulocyte colony-stimulating factor with trimeric-structured methoxy polyethylene glycol N-hydroxysuccinimidyl functional group

The individual positional isomers from the mono-PEGylated recombinant human granulocyte colony-stimulating factor (rhG-CSF) were successfully isolated with additional strong cation exchange chromatography using Source 15S. The three isolated individual positional isomers were found to be homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), analytical size exclusion high-performance liquid chromatography (SE-HPLC), and analytical cation exchange HPLC (CIE-HPLC) and were also characterized with respect to site of PEGylation by enzymatic digestion with endoproteinase Lys-C and N-terminal sequencing. In addition, in vitro biological activity was determined by cell proliferation assay. It was determined that the three isolated individual positional isomers were PEGylated at Lys35, Met(N-terminal), and Lys17 of the rhG-CSF molecule with a 23-kDa trimer-structured methoxy polyethylene glycol N-hydroxysuccinimidyl functional group (mPEG-NHS). All individual positional isomers (Lys35-PEGylated rhG-CSF, Met(N-terminal)-PEGylated rhG-CSF, and Lys17-PEGylated rhG-CSF) retained in vitro biological activity and were found to be 18.5%, 37.6%, and 7.1%, respectively, compared with the rhG-CSF molecule. The significantly different in vitro biological activities observed in the individual positional isomers could be presumably due to interference of receptor binding or active sites on the rhG-CSF molecule. In conclusion, the individual positional isomers isolated from the mono-PEGylated rhG-CSF were well characterized with respect to the site of PEGylation involving Lys35, Met(N-terminal), and Lys17. This characterization of the individual positional isomers would be critical to provide a basis for establishing consistency in the manufacturing process.     

A novel solid-phase site-specific PEGylation enhances the in vitro and in vivo biostabilty of recombinant human keratinocyte growth factor 1

Keratinocyte growth factor 1 (KGF-1) has proven useful in the treatment of pathologies associated with dermal adnexae, liver, lung, and the gastrointestinal tract diseases. However, poor stability and short plasma half-life of the protein have restricted its therapeutic applications. While it is possible to improve the stability and extend the circulating half-life of recombinant human KGF-1 (rhKGF-1) using solution-phase PEGylation, such preparations have heterogeneous structures and often low specific activities due to multiple and/or uncontrolled PEGylation. In the present study, a novel solid-phase PEGylation strategy was employed to produce homogenous mono-PEGylated rhKGF-1. RhKGF-1 protein was immobilized on a Heparin-Sepharose column and then a site-selective PEGylation reaction was carried out by a reductive alkylation at the N-terminal amino acid of the protein. The mono-PEGylated rhKGF-1, which accounted for over 40% of the total rhKGF-1 used in the PEGylation reaction, was purified to homogeneity by SP Sepharose ion-exchange chromatography. Our biophysical and biochemical studies demonstrated that the solid-phase PEGylation significantly enhanced the in vitro and in vivo biostability without affecting the over all structure of the protein. Furthermore, pharmacokinetic analysis showed that modified rhKGF-1 had considerably longer plasma half-life than its intact counterpart. Our cell-based analysis showed that, similar to rhKGF-1, PEGylated rhKGF-1 induced proliferation in NIH 3T3 cells through the activation of MAPK/Erk pathway. Notably, PEGylated rhKGF-1 exhibited a greater hepatoprotection against CCl(4)-induced injury in rats compared to rhKGF-1.     

Site-specific PEGylation of a lysine-deficient TNF-alpha with full bioactivity

Addition of polyethylene glycol to protein (PEGylation) to improve stability and other characteristics is mostly nonspecific and may occur at all lysine residues, some of which may be within or near an active site. Resultant PEGylated proteins are heterogeneous and can show markedly lower bioactivity. We attempted to develop a strategy for site-specific mono-PEGylation using tumor necrosis factor-alpha (TNF-alpha). We prepared phage libraries expressing TNF-alpha mutants in which all the lysine residues were replaced with other amino acids. A fully bioactive lysine-deficient mutant TNF-alpha (mTNF-alpha-Lys(-)) was isolated by panning against TNF-alpha-neutralizing antibody despite reports that some lysine residues were essential for its bioactivity. mTNF-alpha-Lys(-) was site-specifically mono-PEGylated at its N terminus. This mono-PEGylated mTNF-alpha-Lys(-), with superior molecular uniformity, showed higher bioactivity in vitro and greater antitumor therapeutic potency than randomly mono-PEGylated wild-type TNF-alpha. These results suggest the usefulness of the phage display system for creating functional mutant proteins and of our site-specific PEGylation approach.     

Optimal site-specific PEGylation of mutant TNF-alpha improves its antitumor potency

Recently, we created a lysine-deficient mutant tumor necrosis factor-alpha [mTNF-alpha-Lys(-)] with full bioactivity in vitro compared with wild-type TNF-alpha (wTNF-alpha), and site-specific PEGylation of mTNF-alpha-Lys(-) was found to selectively enhance its in vivo antitumor activity. In this study, we attempted to optimize this PEGylation of mTNF-alpha-Lys(-) to further improve its therapeutic potency. mTNF-alpha-Lys(-) was site-specifically modified at its N-terminus with linear polyethylene glycol (LPEG) or branched PEG (BPEG). While randomly mono-PEGylated wTNF-alpha (ran-LPEG5K-wTNF-alpha) with 5 kDa of LPEG (LPEG5K) had about only 4% in vitro bioactivity of wTNF-alpha, mono-PEGylated mTNF-alpha-Lys(-) [sp-PEG-mTNF-alpha-Lys(-)] with LPEG5K, LPEG20K, BPEG10K, and BPEG40K had 82%, 58%, 93%, and 65% bioactivities of mTNF-alpha-Lys(-), respectively. sp-LPEG-mTNF-alpha-Lys(-) and sp-BPEG10K-mTNF-alpha-Lys(-) had much superior antitumor activity to those of both unmodified TNF-alphas and ran-LPEG5K-wTNF-alpha, though sp-BPEG40K-mTNF-alpha-Lys(-) did not show in vivo antitumor activity. Thus, the molecular shape and weight of PEG may strongly influence the in vivo antitumor activity of sp-PEG-mTNF-alpha-Lys(-).     

Automated mass spectrometric analysis of urinary free catecholamines using on-line solid phase extraction

Analysis of catecholamines (epinephrine, norepinephrine and dopamine) in plasma and urine is used for diagnosis and treatment of catecholamine-producing tumors. Current analytical techniques for catecholamine quantification are laborious, time-consuming and technically demanding. Our aim was to develop an automated on-line solid phase extraction method coupled to high performance liquid chromatography–tandem mass spectrometry (XLC–MS/MS) for the quantification of free catecholamines in urine. Five microlitre urine equivalent was pre-purified by automated on-line solid phase extraction, using phenylboronic acid complexation. Reversed phase (pentafluorophenylpropyl column) chromatography was applied. Mass spectrometric detection was operated in multiple reaction monitoring mode using a quadrupole tandem mass spectrometer with positive electrospray ionization. Urinary reference intervals were set in 24-h urine collections of 120 healthy subjects. XLC–MS/MS was compared with liquid chromatography with electrochemical detection (HPLC–ECD). Total run-time was 14 min. Intra- and inter-assay analytical variations were <10%. Linearity was excellent (R² > 0.99). Quantification limits were 1.47 nmol/L, 15.8 nmol/L and 11.7 nmol/L for epinephrine, norepinephrine and dopamine, respectively. XLC–MS/MS correlated well with HPLC–ECD (correlation coefficient >0.98). Reference intervals were 1–10 μmol/mol, 10–50 μmol/mol and 60–225 μmol/mol creatinine for epinephrine, norepinephrine and dopamine, respectively. Advantages of the XLC–MS/MS catecholamine method include its high analytical performance by selective PBA affinity and high specificity and sensitivity by unique MS/MS fragmentation.     

Phase behaviour of stearic acid-stearonitrile mixtures: A thermodynamic study in bulk and at the air-water interface

The solid-liquid phase behaviour of stearic acid (SA) and stearonitrile (SN) in binary mixtures was investigated by differential scanning calorimetry (DSC), and the formation of SA-SN mixed monolayers at the air-water interface was followed by surface pressure-area (π-A) measurements and by Brewster angle microscope (BAM) observation. The solid-liquid phase diagram is a eutectic type phase diagram, with the eutectic composition 0.90 < X_SN < 0.95 and T^eut = 40.9 °C. The DSC results also suggest that the two components are immiscible in the solid phase but form a liquid mixture with positive deviations to the ideal behaviour. At the air-water interface, the two components form liquid condensed monolayers in the entire range of compositions, at low surface pressures, while solid mixed monolayers only form at high surface pressures for X_SN < 0.8. Thermodynamic analysis indicates that SA and SN are miscible in the liquid condensed phase, with negative deviations from the ideal behaviour. The variation of the collapse surface pressure of mixed monolayers also indicates miscibility at the air-water interface.     

Mono-PEGylation of ribonuclease A: High PEGylation efficiency by thiolation with small molecular weight reagent

PEGylation can improve the therapeutic potential of ribonuclease A (RNase A), a cancer chemotherapeutic agent. However, the common PEGylation that targets at the ?-amino groups of proteins can lead to imprecise control of the stoichiometry of the protein-PEG conjugate (i.e., mono-, di- and multi-PEGylated protein). To prepare a PEGylated therapeutic protein, it is desirable that the protein is mono-PEGylated for industrial production, convenient purification and analytical characterization. Here, N-hydroxysuccinimide esters of S-acetylthioacetic acid (SATA) and 2-iminothiolane (IT) were used to introduce thiol groups on RNase A, followed by maleimide chemistry based PEGylation of the thiolated RNase A. Interestingly, the yield of mono-PEGylated RNase A was higher than 60%, and di- or multi-PEGylated RNase A were absent in the PEGylated product. Presumably, the limited number and low solvent accessibility of the introduced thiol group favored mono-PEGylation of RNase A. As compared to the unmodified RNase A, the mono-PEGylated RNase A showed slightly decreased enzymatic activity, increased anti-proliferative ability and unchanged structural properties. Our study is expected to control the PEGylation process and optimize the industrial pharmaceutical production of PEGylated proteins.     

Development and validation of a sensitive ultra performance liquid chromatography tandem mass spectrometry method for the analysis of fentanyl and its major metabolite norfentanyl in urine and whole blood in forensic context

Fentanyl and its major metabolite norfentanyl often occur in low doses in biological samples. Therefore, a highly sensitive liquid chromatography tandem mass spectrometry (LC–MS/MS) method has been developed and fully validated. Sample preparation was performed on a mixed-mode cation exchange solid phase extraction (SPE) cartridge with an additional alkaline wash step to decrease matrix effects and thus increase sensitivity. Ionization of fentanyl and norfentanyl with electrospray ionization (ESI) was more efficient than atmospheric pressure chemical ionization (APCI). The use of a mobile phase of high pH resulted in higher ESI signals than the conventional low pH mobile phases. In the final method, gradient elution with 10 mM ammonium bicarbonate (pH 9) and methanol was performed. A comparison of columns with different internal diameter and/or smaller particles showed optimal resolution and sensitivity when an Acquity C18 column (1.7 μm, 2.1 mm × 50 mm) was used. Deuterium labeled internal standards were used, but with careful evaluation of their stability since loss of deuteriums was seen. With limits of detection of 0.25 pg/ml for fentanyl and 2.5 pg/ml for norfentanyl in urine and 5 pg/ml for fentanyl and norfentanyl in whole blood the presented method is highly appropriate for the analysis of fentanyl and norfentanyl in forensic urine and blood samples.     

Determination of stability constants between complexing agents and At(I) and At(III) species present at ultra-trace concentrations

A competition method is proposed to determine the complexation constants between At(I) and At(III) species and complexing agents. The method, tested with an inorganic ligand, thiocyanate ion (SCN⁻), and an organic macromolecule, thiacalix[4]arenetetrasulfonate (LH₄) is based on solid/liquid separation or liquid/liquid extraction. For the solid/liquid separation, the cationic exchanger Dowex 50X8 was used. The interaction of At(I) and At(III) with the cationic exchanger is specific but could not be described by the expected cation exchange process. Most probably, At(I, III) interacts with a “strong” site (in weak amount) to form a surface complex at the surface of the resin organic skeleton. For the liquid/liquid separation, chloroform, toluene and hexane were used. All solvents extract astatine species with distribution coefficients varying between 0.7 and 120. The extraction process was shown to be independent of aqueous phase characteristics (pH, ionic strength) and was explained by the solvation of astatine species by the organic solvent. The effect of the addition of the thiacalix[4]arenetetrasulfonate on the solid/liquid or liquid/liquid distribution coefficients could be well described by the formation of a 1:1 complex with stability constants of log β₁ = 4.5 ± 0.4 and 3.3 ± 0.3 for At(I) and At(III), respectively. For the thiocyanate ion, the data measured in the presence of the organic solvents could be explained by the formation of both 1:1 and 1:2 At:SCN complexes. In the case of the solid/liquid separation, data analysis was hampered by the probable formation of a ternary complex between At(I, III), SCN⁻ and the functional groups of the resin. As for the calixarene, the interaction strength appeared slightly higher for At(I) (log β₂ = 5.9 ± 0.3 and log β₁ = 3.8 ± 0.2 for 1:2 and 1:1 complexed species, respectively) than for At(III) (log β₂ = 5.3 ± 0.2 and log β₁ = 2.8 ± 0.2 for 1:2 and 1:1 complexed species, respectively).     

Phase studies of model biomembranes: Complex behavior of DSPC/DOPC/Cholesterol

We have undertaken a series of experiments to examine the behavior of individual components of cell membranes. Here we report an initial stage of these experiments, in which the properties of a chemically simple lipid mixture are carefully mapped onto a phase diagram. Four different experimental methods were used to establish the phase behavior of the 3-component mixture DSPC/DOPC/chol: (1) confocal fluorescence microscopy observation of giant unilamellar vesicles, GUVs; (2) FRET from perylene to C20:0-DiI; (3) fluorescence of dilute dyes C18:2-DiO and C20:0-DiI; and (4) wide angle X-ray diffraction. This particular 3-component mixture was chosen, in part, for a high level of immiscibility of the components in order to facilitate solving the phase behavior at all compositions. At 23 °C, a large fraction of the possible compositions for this mixture give rise to a solid phase. A region of 3-phase coexistence of {Lα + Lβ + Lo} was detected and defined based on a combination of fluorescence microscopy of GUVs, FRET, and dilute C20:0-DiI fluorescence. At very low cholesterol concentrations, the solid phase is the tilted-chain phase Lβ′. Most of the phase boundaries have been determined to be within a few percent of the composition. Measurements of the perturbations of the boundaries of this accurate phase diagram could serve as a means to understand the behaviors of a range of added lipids and proteins.     

Influence of variables in the hydrothermal treatment of rice straw on the composition of the resulting fractions

The influence of the hydrothermal treatment conditions of rice straw (temperature – 150–190 °C , time – 0–20 min after reaching the operation temperature – and liquid/solid ratio – 6–8), on the composition of liquid and solid fractions was studied. Polynomial models were found for to reproduce the experimental results with errors less than 6%.     

溶葡球菌酶的定点突变与PEG巯基定点修饰

为了建立聚乙二醇 (PEG) 巯基定点修饰溶葡球菌酶的方法,并检验假定连接区的突变与修饰对酶活的影响,对溶葡球菌酶的假定连接区进行了巯基聚乙二醇定点修饰研究。通过分析溶葡球菌酶的结构特征,选择两个结构域之间的氨基酸 (133-154aa) 进行定点突变引入半胱氨酸残基。使用单甲氧基聚乙二醇马来酰亚胺 (mPEG-MAL) 进行定点修饰,对修饰后的酶进行纯化并测定酶活性。结果表明定点突变的半胱氨酸残基PEG修饰效率高、产物单一,运用简便的Ni2+-NTA柱亲和层析法实现了一步分离,获得了高纯度的目标蛋白,但在连接区进行定点突变及PEG定点修饰后的酶活有不同程度的降低,表明假定连接区部分位点的PEG修饰会对溶葡球菌酶的催化活性产生一定影响。     

Linker-Extended Native Cyanovirin-N Facilitates PEGylation and Potently Inhibits HIV-1 by Targeting the Glycan Ligand

Cyanovirin-N (CVN) potently inhibits human immunodeficiency virus type 1 (HIV-1) infection, but both cytotoxicity and immunogenicity have hindered the translation of this protein into a viable therapeutic. A molecular docking analysis suggested that up to 12 residues were involved in the interaction of the reverse parallel CVN dimer with the oligosaccharide targets, among which Leu-1 was the most prominent hot spot residue. This finding provided a possible explanation for the lack of anti-HIV-1 activity observed with N-terminal PEGylated CVN. Therefore, linker-CVN (LCVN) was designed as a CVN derivative with a flexible and hydrophilic linker (Gly₄Ser)₃ at the N-terminus. The N-terminal α-amine of LCVN was PEGylated to create 10 K PEG-aldehyde (ALD)-LCVN. LCVN and 10 K PEG-ALD-LCVN retained the specificity and affinity of CVN for high mannose N-glycans. Moreover, LCVN exhibited significant anti-HIV-1 activity with attenuated cytotoxicity in the HaCaT keratinocyte cell line and MT-4 T lymphocyte cell lines. 10 K PEG-ALD-LCVN also efficiently inactivated HIV-1 with remarkably decreased cytotoxicity and pronounced cell-to-cell fusion inhibitory activity in vitro. The linker-extended CVN and the mono-PEGylated derivative were determined to be promising candidates for the development of an anti-HIV-1 agent. This derivatization approach provided a model for the PEGylation of biologic candidates without introducing point mutations.     

PEG chain length impacts yield of solid-phase protein PEGylation and efficiency of PEGylated protein separation by ion-exchange chromatography: Insights of mechanistic models

The mechanisms behind protein PEGylation are complex and dictated by the structure of the protein reactant. Hence, it is difficult to design a reaction process which can produce the desired PEGylated form at high yield. Likewise, efficient purification processes following protein PEGylation must be constructed on an ad hoc basis for each product. The retention and binding mechanisms driving electrostatic interaction-based chromatography (ion-exchange chromatography) of PEGylated proteins (randomly PEGylated lysozyme and mono-PEGylated bovine serum albumin) were investigated, based on our previously developed model Chem. Eng. Technol. 2005, 28, 1387–1393. PEGylation of each protein resulted in a shift to a smaller elution volume compared to the unmodified molecule, but did not affect the number of binding sites appreciably. The shift of the retention volume of PEGylated proteins correlated with the calculated thickness of PEG layer around the protein molecule. Random PEGylation was carried out on a column (solid-phase PEGylation) and the PEGylated proteins were separated on the same column. Solid-phase PEGylation inhibited the production of multi-PEGylated forms and resulted in a relatively low yield of selective mono-PEGylated form. Pore diffusion may play an important role in solid-phase PEGylation. These results suggest the possibility of a reaction and purification process development based on the mechanistic model for PEGylated proteins on ion exchange chromatography.     

A new modified Edman procedure for analysis of N-terminal valine adducts in hemoglobin by LC–MS/MS

A rapid and sensitive method using liquid chromatography–tandem mass spectrometry (LC–MS/MS) for simultaneous determination of adducts from acrylamide, glycidamide and ethylene oxide to N-terminal valines in hemoglobin (Hb) was developed. This new procedure is based on the same principles as the N-alkyl Edman procedure for analysis of adducts from electrophilic agents to N-terminal valines in Hb. The N-substituted valines can be detached, enriched and measured selectively as thiohydantoins by the use of an Edman reagent, in this case fluorescein isothiocyanate (FITC). This procedure is denoted as the “adduct FIRE procedure” as the FITC reagent is used for measurement of adducts (R) formed from electrophilic compounds with a modified Edman procedure. In this study, fluorescein thiohydantoin (FTH) analytes of N-substituted valines from acrylamide, glycidamide and ethylene oxide, as well as their corresponding hepta- and tri-deuterium-substituted analogues, were synthesized. These analytes (n = 8) were then characterized by LC–MS/MS (ESI, positive ion mode) and obtained product ions were interpreted. A considerable work with optimization of the FIRE procedure™, resulted in a procedure in which low background levels of the studied adducts could be measured from 250 μL lyzed whole blood samples (human non-smokers). The analytes were enriched and purified with solid phase extraction columns and analyzed by LC–MS/MS with LOQ down to 1 pmol adduct/g Hb. Compared to other procedures for determination of N-terminal Hb adducts, the introduction of FITC has led to a simplified procedure, where whole blood also can be used, giving new opportunities and reduced hand on time with increased sample throughput.     

Investigation of α-phenylnorstatine and α-benzylnorstatine as transition state isostere motifs in the search for new BACE-1 inhibitors

Inhibition of the BACE-1 protease enzyme has over the recent decade developed into a promising drug strategy for Alzheimer therapy. In this report, more than 20 new BACE-1 protease inhibitors based on ??-phenylnorstatine, ??-benzylnorstatine, iso-serine, and ??-alanine moieties have been prepared. The inhibitors were synthesized by applying Fmoc solid phase methodology and evaluated for their inhibitory properties. The most potent inhibitor, tert-alcohol containing (R)-12 (IC₅₀ = 0.19 ??M) was co-crystallized in the active site of the BACE-1 protease, furnishing a novel binding mode in which the N-terminal amine makes a hydrogen bond to one of the catalytic aspartic acids.