Facile Access to Multisensitive and Self-Healing Hydrogels with Reversible and Dynamic Boronic Ester and Disulfide Linkages.

Multifunctional and multiresponsive hydrogels have presented a promising platform to design and fabricate smart devices for application in a wide variety of fields. However, their preparations often involve multistep preparation of multiresponsive polymer precursors, tedious reactions to introduce functional groups or sophisticated molecular designs. In this work, a multifunctional boronic acid-based cross-linker bis(phenylboronic acid carbamoyl) cystamine (BPBAC) was readily prepared from inexpensive commercially available 3-carboxylphenylboronic acid (CPBA) and cystamine dihydrochloride, which has the ability to cross-link the cis-diols and catechol-containing hydrophilic polymers to form hydrogels. Due to the presence of the reversible and dynamic boronate ester and disulfide bonds, the obtained hydrogels were demonstrated to not only possess pH, glucose, and redox triresponsive features, but also have autonomic self-healing properties under ambient conditions. Moreover, we can modulate the rheological and mechanical properties by simply adjusting the BPBAC amount. The features, such as commercially available starting materials, easy-to-implement approach, and versatility in controlling cross-linking network and mechanical properties, make the strategy described here a promising platform for fabricating multifunctional and smart hydrogels.

Selenium and sulfur in exchange reactions: a comparative study.

Cysteamine reduces selenocystamine to form hemiselenocystamine and then cystamine. The rate constants are k(1) = 1.3 × 10(5) M(-1) s(-1); k(-1) = 2.6 × 10(7) M(-1) s(-1); k(2) = 11 M(-1) s(-1); and k(-2) = 1.4 × 10(3) M(-1) s(-1), respectively. Rate constants for reactions of cysteine/selenocystine are similar. Reaction rates of selenium as a nucleophile and as an electrophile are 2-3 and 4 orders of magnitude higher, respectively, than those of sulfur. Sulfides and selenides are comparable as leaving groups.

Epoxy-amine synthesised hydrogel scaffolds for soft-tissue engineering.

Highly porous and biodegradable hydrogels based on poly(ethylene glycol) (PEG) and cystamine (Cys) were fabricated using epoxy-amine chemistry and investigated as scaffolds for soft-tissue engineering. Whereas the application of fused-salt templates provided a comprehensive interconnecting pore morphology, the incorporation of a specially designed poly(epsilon-caprolactone) (PCL) cross-linker provided enhanced mechanical function without adversely effecting the scaffolds positive biological interactions. The addition of only 1.2 wt% of the PCL cross-linker was sufficient to provide improvements in the ultimate stress of 30-40%. In vitro studies not only confirmed the non-cytotoxic nature of the scaffolds, but also their degradation products, which were isolated and characterised by nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionisation time-of-flight mass spectroscopy (MALDI ToF MS). In vivo trials were conducted over a period of 8 weeks through implantation of the scaffolds into the dorsal region of rats. At both 2 and 8 week time points the explants revealed complete infiltration by the surrounding tissue and the development of a vascular network to support the newly generated tissue, without an excessive foreign-body response.

A general fluorescence-based coupled assay for S-adenosylmethionine-dependent methyltransferases.

We have developed a simple and sensitive fluorescence-based two-step coupled enzyme assay to report the activity of S-adenosylmethionine-dependent methyltransferases. This assay relies on a fluorescein-cystamine-methyl red (FL-S-S-MR) reporter molecule that can be activated by thiols. In the absence of thiols, fluorescence from the reporter is quenched through fluorescence resonance energy transfer between the two chromophores. In this report, we use catechol-O-methyltransferase with the addition of S-adenosylhomocysteine hydrolase to produce the thiol homocysteine. The presence of homocysteine leads to disulfide bond cleavage in the cystamine tether and fluorescence dequenching as the uncoupled chromophores are diluted into the surrounding media. The sensitivity and specificity of FL-S-S-MR to thiols enabled detection of

Palladium-mediated C5 substitution of pyrimidine nucleosides.

One of the most efficient ways to link a reporter group to oligonucleotides is through the incorporation of a modified nucleoside during automated oligonucleotide synthesis. To be useful, it is important that the reporter group not interfere in hybridization reactions. This unit describes two linkers that can be used for the incorporation of a reporter group at the C5 position of deoxyuridine: a flexible aminoethylthioether linker, and a rigid amidopropynyl linker. The latter is sufficiently long and positioned so that the reporter group lies outside the major groove of the DNA duplex.

Synthesis and antitumour effect of the melanogenesis-based antimelanoma agent N-propionyl-4-S-cysteaminylphenol.

Chemotherapy of malignant melanoma is still a great challenge, as no effective drugs are available. The development of melanogenesis-based drugs is a promising area of research because melanogenesis is a unique biochemical pathway operating only in melanoma cells (and their normal counterparts) so that the tumour can be targeted. We have been using cysteinylphenol, a sulphur-containing analogue of tyrosine, and derivatives for that purpose. N-Acetyl-4-S-cysteaminylphenol was found to have the best antimelanoma effect in cell culture systems and in mice bearing B16 melanoma tumours. It also caused depigmentation of the skin, suggesting the possibility of use as a hypopigmenting agent. To improve the efficiency of the drug, we thought of replacing the acetyl group in N-acetyl-4-S-cysteaminylphenol with a propionyl group in the hope that increased hydrophobicity would increase the cellular uptake of the drug. N-Propionyl-4-S-cysteaminylphenol was synthesized by condensing 4-hydroxythiophenol with 2-ethyl-2-oxazoline. The drug showed both cytostatic and cytocidal effects in a human melanotic melanoma cell line. The drug was found to be a good depigmenting agent for the black hair follicles of C57 black mice when given s.c. for 14 days. A 10-day treatment with N-propionyl-4-S-cysteaminylphenol at 300 mg/kg body weight reduced the growth rate of B16 melanoma s.c. tumours in mice by 36%. The propionyl derivative was found to increase the life span of mice bearing melanoma more effectively than did the acetyl derivative.

Application of cystamine and N,N'-Bis(glycyl)cystamine as linkers in polysaccharide-protein conjugation.

Pneumococcal polysaccharide type 6B, 14, or 23F (35-70 kDa) was activated with cyanogen bromide and modified with cystamine. After reduction of the spacer, the thiol-containing (i.e. cysteamine-modified) polysaccharide obtained was added in a 5-10-fold molar excess to bromoacetylated tetanus toxoid to give thioether-linked polysaccharide-protein conjugates in a yield of 10-20%. This approach failed for preparing a type 19F polysaccharide-protein conjugate, possibly due to intramolecular elimination of cysteamine from the reduced 19F polysaccharide. When N,N'-bis(glycyl)cystamine was introduced as a spacer molecule, the elimination of the reduced spacer was suppressed, thus allowing preparation of a 19F polysaccharide-tetanus toxoid conjugate (15%).

The effect of a cystamine derivative, bis[2-(E-2-hexenoylamino)ethyl] disulfide, on rat platelet aggregation.

Bis[2-(E-2-alkenoylamino)ethyl] disulfides (compds. I), synthesized from cystamine and 2-trans fatty acids, inhibited collagen-induced rat and rabbit platelet aggregation. The most potent compound was bis[2-(E-2-hexenoylamino)ethyl] disulfide (compd. I-1), and this compound suppressed thromboxane B2 formation from arachidonic acid in rat platelets. The results suggested that compd. I-1 has an inhibitory effect on cyclooxygenase.

Synthesis and radioprotective activity of dipeptide cysteamine and cystamine derivatives.

Some N-(dipeptidyl)-S-acetylcysteamine and N,N'-(dipeptidyl)cystamine salt derivatives were synthesized and evaluated as candidate radioprotector agents. Toxicity and radioprotective activity as the dose reduction factor (DRF) were determined in vivo on mice and compared to N-glycyl-S-acetylcysteamine trifluoroacetate. One of the most interesting compounds of this series was N-glycylglycyl-S-acetylcysteamine trifluoroacetate (8).

Photochemical crosslinking of protein and DNA in chromatin. II. Synthesis and application of psoralen-cystamine-arylazido photocrosslinking reagents.

The synthesis and testing of a new type of nucleic acid-protein photocrosslinking reagent is described. The reagents are composed of a psoralen ligand for nucleic acid photoattachment, which is linked to an azidobenzoyl group, for protein photoattachment. The linker contains a disulfide bridge which can be opened by reduction with mercaptans. The reagents were tested in a chromatin system, where it was found that they induced cleavable crosslinks between the histones and the DNA upon irradiation with long-wavelength ultraviolet light (lambda greater than 300 nm).

Synthesis and chromatographic properties of 1,3-thiazane-2-carboxylic acid (beta-homothiaproline).

Details are reported for the synthesis of 1,3-thiazane-2-carboxylic acid, or beta-homothiaproline, 3-Bromopropylamine is allowed to react with sodium thiosulfate to give S-sulfo-homocysteamine, which is then split in acidic medium to homocystamine. Homocystamine is reduced by a slight excess of dithioerythritol and allowed to react with sodium glyoxylate. beta-Homothiaproline is then isolated by ion exchange on Dowex 50 and finally obtained in pure crystalline form, with a fairly good yield. Some chemical and chromatographic properties of beta-homothiaproline, in comparison with gamma-homothiaproline (1,3-thiazane-4-carboxylic acid), beta-thiaproline (thiazolidine-2-carboxylic acid) and gamma-thiaproline (thiazolidine-4-carboxylic acid) are described.

Synthesis and properties of N-acetyl-N'-(p-glyoxylylbenzoyl)cystamine, a new reagent for RNA-RNA and RNA-protein cross-linking.

The synthesis of N-acetyl-N'-(p-glyoxylylbenzoyl)cystamine (Gbz-Cyn2-Ac) is described. Like other glyoxal-type reagents it reacts with guanine and arginine. The kinetics and pH dependence of these reactions are studied. (Gbz-Cyn2-Ac) reacts with non-base-paired guanines at about 20 sites in 16-S rRNA. After reduction of disulfide bonds each derivatized guanine residue carries a free -- SH group which can be used to create RNA-RNA bridges or, after introducing an additional photoactivatable derivative, RNA-protein bridges.

Molecular properties of the adrenergic alpha-receptor. I--Structural requirements for specific covalent occupancy by N,N'-bis--(5-aminopentyl)cystamine derivatives.

The synthesis and alpha-adrenoreceptor blocking activity of several substituted analogs of the prototype alpha-blocker N,N'-bis-(5-aminopentyl)cystamine (APC) are described. The three optical forms of the analog carrying methyl groups on the carbons alpha- to the sulfurs were synthesized and shown to be equipotent and somewhat less active than APC. The omega, omega'-bis-guanidino analog of APC was less active. Significant improvement in potency was observed only with APC analogs carrying benzyl and substituted benzyl groups on the terminal nitrogens. Linking the terminal nitrogens of APC with a p.xyledenyl group so as to give the 26-membered analog caused a sharp drop in activity. The significance of these results as regards the alpha-receptor topography is discussed.