Application of parylene for surface (polymer) enhanced laser desorption/ionization of synthetic polymers

RATIONALE

Synthetic polymers of molecular masses up to a few kDa can be analyzed without the use of any matrix by direct laser desorption/ionization mass spectrometry (LDI-MS). In this technique, the surface of the sample plate plays a crucial role, and many attempts have been made to understand the influence of the surface on the ease of desorption. Since this technique requires no tedious sample pretreatment, it is a promising method for the rapid characterization of various synthetic polymers.

METHODS

Parylene (poly(p-xylylenes), PPX) was tested as a surface support for studying the molecular masses of biocompatible polymers: poly(ethylene glycol) (PEG), poly(L-lactide) (PLLA), and poly(methyl methacrylate) (PMMA). The average molecular masses of the polymers were: PEG (600.0 Da and 3.5 kDa), PMMA (2.0 kDa), and PLLA (2.8 kDa).

RESULTS

LDI mass spectra of polymers deposited on parylene were enhanced by a factor of two over those obtained directly from the gold target plate.

CONCLUSIONS

Modification of the surface of the target plate by the addition of a PPX layer extended the functionality of LDI-TOF MS, especially for the analysis of low-mass compounds. The LDI analysis using the PPX-coated target plate provided details of polymers including: end-group, composition, monomer unit, and molecular mass distribution. The average molecular weights of four tested polymers on the gold target plate and the PPX support were unchanged, indicating that sample degradation was not occurring despite the high energy of the laser beam. The LDI investigations showed that the PPX support boosted ion yields by a factor of two compared with the gold target plate.

Differentiation of diastereoisomers of protected 1,2-diaminoalkylphosphonic acids by EI mass spectrometry and density functional theory

Electron ionization mass spectrometry and density functional theory (DFT) calculations have been used to study the fragmentation of diastereoisomers of protected 1,2-diaminoalkylphosphonic acids. The loss of a diethoxyphosphoryl group and the elimination of diethyl phosphonate were found to be competitive fragmentation processes, which can be used to differentiate both stereoisomers. Selective deuterated analogs and product- and precursor-ion mass spectra allowed the elucidation of the fragmentation mechanisms. The structures of the transition states and product ions were optimized using the density functional theory (DFT), and free energy calculations confirmed the observed differences in the formation and relative intensities of specific fragment ions.

Stereochemical effects in fragmentation of diastereoisomers of protected diethyl 1,2-diamino-alkylphosphonates

Diastereoisomers of diethyl 5-substituted (2-thioxo-imidazolidin-4-yl)phosphonates, which can be regarded as protected diethyl 1,2-diaminoalkylphosphonates, have been analyzed by electron ionization mass spectrometry. Significant differences in the fragmentation of cis- and trans-diastereoisomers were found. The stereospecificity of the elimination of diethyl phosphonate and the loss of the diethoxyphosphoryl group were studied using specific labeled compounds and collision-induced dissociation. The relative abundances of ions formed via these fragmentation processes can be used for differentiation of both diastereoisomers.

Solid-state NMR spectroscopy as a tool supporting optimization of MALDI-TOF MS analysis of polylactides

We report systematic structural studies of poly(l-lactide) (PLLA) employing matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and solid-state NMR spectroscopy. (13)C cross polarization magic angle spinning (CP/MAS) NMR data for 1,8-dihydroxy-9-anthracenone (DT), 2,5-dihydroxybenzoic acid (DHB), 2-(4-hydroxyphenylazo)-benzoic acid (HABA), and trans-3-indoleacrylic acid (IAA), four matrices commonly used in MALDI-TOF analysis of polymers, were analyzed to test the influence of crystallization conditions (solvent, inorganic salt) on sample morphology. (13)C principal elements of chemical shift tensor (CST) and line-shape analyses were employed to study of the nature of hydrogen bonding and to evaluate the crystallinity and amorphicity of the pure polymer. NMR parameters for PLLA were compared with data for polylactide crystallized with the four matrices under different conditions with the addition of two inorganic salts as cationization agents. This study revealed that the semicrystalline structure of the polymer does not change when it is embedded in the matrix.

Analogues of cyclolinopeptide A containing alpha-hydroxymethyl amino acid residues

Linear and cyclic cyclolinopeptide A (CLA) analogues containing alpha-hydroxymethylleucine (HmL) in positions 1, 4, and 1&4, and alpha-hydroxymethylvaline (HmV) in position 5, were synthesized by the solid-phase peptide strategy and cyclized with the 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide/1-hydroxy-7-azabenzotriazole (EDC/HOAt) reagent. The peptides were examined for their immunosuppressive activity in the lymphocyte proliferation assays (LPA). Only HmL-containing peptides demonstrated at about 25% lower immunosuppressive activity, but they are four times more soluble in water solutions than the native CLA. It seems from the LPA results that peptide [(HmL4)CLA] is the most promising for further studies. This peptide was characterized in solution, at room temperature in CDCl3, and the conformation compared with that observed for CLA in the solid state.

Flavonoids from Ficaria verna Huds

A phytochemical investigation of the flowers and leaves of Ficaria verna Huds. (Ranunculaceae) yielded four additional known flavonoid compounds including: kaempferol 3-O-beta-D-(6"-a-L-rhamnopyranosyl)-glucopyranoside (nicotiflorin), apigenin 8-C-beta-D-glucopyranoside (vitexin), luteolin 8-C-beta-D-glucopyranoside (orientin) and apigenin 8-C-beta-D-(2"-O-beta-D-glucopyranosyl)-glucopyranoside (flavosativaside). The characterisation of these compounds was achieved by various chromatographic and spectroscopic methods (UV, 1H NMR, 13C NMR and MS).

Purification, cloning, and characterization of the 16S RNA m5C967 methyltransferase from Escherichia coli

The methyltransferase that forms m5C967 in Escherichia coli small subunit ribosomal RNA has been purified, cloned, and characterized. The gene was identified from the N-terminal sequence of the purified enzyme. The gene is a fusion of two open reading frames, fmu and fmv, previously believed to be distinct due to a DNA sequencing error. The gene, here named rsmB, encodes a 429-amino acid protein that has a number of homologues in prokaryotes, Archaea, and eukaryotes. C-Terminal sequencing of the overexpressed and affinity-purified protein by mass spectrometry methods verified the sequence expected for the gene product. The recombinant protein exhibited the same specificity as the previously described native enzyme; that is, it formed only m5C and only at position 967. C1407, which is also m5C in natural 16S RNA, was not methylated. In vitro, the enzyme only recognized free 16S RNA. 30S ribosomal subunits were not a substrate. There was no requirement for added magnesium, suggesting that extensive secondary or tertiary structure in the RNA substrate may not be a requirement for recognition.

Novel internucleotide 3'-NH-P(CH3)(O)-O-5' linkage. Oligo(deoxyribonucleoside methanephosphonamidates); synthesis, structure and hybridization properties

Diastereomeric dithymidine methanephosphonamidates (TnpmT) were synthesized by reaction of 3'-amino-3'-deoxythymidine with 3'- O -acetylthymidin-5-yl-methanephosphonochloridate. Separated dinucleotide TnpmT(fast) and TnpmT(slow) diastereomers were used as building blocks to prepare chimeric dodecathy-midylates, possessing one to four modified linkages, by means of phosphoramidite automated solid phase synthesis. As expected, the methanephosphonamidate internucleotide linkage is resistant to nuclease P1, snake venom PDE and 3'-exonuclease from human plasma. Degradation of dodecathymidylates possessing modified internucleotide linkages in alternate positions proved the 'hopping' properties of 3'-exonuclease. Oligo(deoxyribonucleotide methanephosphonamidates) were tested for their binding affinity to complementary oligomers in thermal denaturation experiments. All the oligomers showed lower binding affinity to DNA and RNA targets, however, oligomers originating from the TnpmT(fast) dimeric unit exhibited better hybridization properties than their diastereomeric TnpmT(slow) counterparts. A lowering of T m of approximately 2.4 degrees C (1.0-1.8 degrees C) was observed for each introduced TnpmT(fast) modification and 6.0 degrees C (4.2-5.0 degrees C) for each TnpmT(slow) modification in duplexes of modified dodecathymidylates with dA12(A12) oligomers. The oligo(deoxyribonucleoside methanephosphonamidate) designated F4, possessing four modified methanephosphonate linkages originating from the TnpmT(fast) diastereomeric unit, exhibits a tendency for triplex formation, as was demonstrated in thermal denaturation experiments with the d(A21C4T21) hairpin oligomer.

Pharmacokinetic-stereoselective differentiation of some isomeric analogues of ifosfamide

Three bromine-ifosfamide analogues: racemic chlorobromofosfamide (+/-)-(R,S)-1, its levorotatory enantiomer (-)-(S)-2 and racemic bromofosfamide (+/-)-(R,S)-3 showed considerable stereoselective differences in their pharmacokinetics and bioavailability depending on the route of administration and regimen of dosage studies in rats. Remarkable differences in the AUCi.p. parameters (212, 54, 89 mumol x min x ml-1, respectively) were demonstrated in comparison with a standard ifosfamide (158 mumol x min x ml-1). However, the AUCp.o. established for (+/-)-(R,S)-1 and (-)-(S)-2 were similar and different from the value measured for (+/-)-(R,S)-3. A wide variability in the determined parameters after i.p. injection and similarities after p.o. administration were finally confirmed by the AUCp.o./AUCi.p. mean ratio which equaled 0.24; 0.79;, 0.54, respectively, as well as by different bioavailability data. The results showed that the pharmacokinetic bioequivalance between i.v. and p.o. treatment is possible to approach by adjustment of fractionated oral dosage.

The practical synthesis of a methylenebisphosphonate analogue of benzamide adenine dinucleotide: inhibition of human inosine monophosphate dehydrogenase (type I and II)

beta-Methylene-BAD (8), a nonhydrolyzable analogue of benzamide adenine dinucleotide (BAD), was synthesized as potential inhibitor of human inosine monophosphate dehydrogenase (IMPDH). Treatment of 2',3'-O-isopropylideneadenosine 5'-methylenebisphosphonate (15) with DCC afforded P1,P4-bis(2',3'-O-isopropylideneadenosine) 5'-P1,P2:P3,P4-dimethylenetetrakisphosphonate (17). This compound was further converted with DCC to an active intermediate 18 which upon reaction with 3-(2',3'-O-isopropylidene-beta-D-ribofuranosyl)benzamide (19) gave, after hydrolysis and deisopropylidenation, the desired beta-methylene-BAD (8) in 95% yield. In a similar manner, treatment of 18 with 2',3'-O-isopropylidenetiazofurin (21) followed by hydrolysis and deprotection afforded beta-methylene-TAD (5) in 91% yield. Compound 8 (IC50 = 0.665 microM) was found to be a 6-8 times less potent inhibitor of IMPDH than 5 (IC50 = 0.107 microM) and was almost equally potent against IMPDH type I and type II. Although TAD and beta-methylene-TAD were bound by LADH with the same affinity, the binding affinity of 8 toward LADH (Ki = 333 microM) was found to be 50-fold lower than that of the parent pyrophosphate 7 (Ki = 6.3 microM).

Formation of the [b+41]+. ion in the mass spectra of 2-thiouridines

In the electron impact mass spectra of some 2-thiouridines a prominent base +41 (b+C2HO) peak was found. The sulphur atom at the 2 position facilitates its formation.