A racemization test in peptide synthesis using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM)

Racemization of the C-terminal amino acid (Ala) has been studied in various solvents during coupling between 4-methoxybenzyloxycarbonyl (Z(OMe))-Gly-L-Ala-OH and phenylalanine benzyl ester (H-Phe-OBzl) with 4-(4,6-dimethoxy-1,3,5-thiazin-2-yl)-4-methylmorpholinium chloride (DMT-MM). The reaction occurred without substantial racemization in AcOEt, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), CH3CN, and 2-PrOH, while a slight racemization was observed in dimethyl sulfoxide (DMSO), EtOH, and MeOH. The extent of racemization may correlate with the polarity of the solvents.     

Enhancement of facilitated olefin transport by amino acid in silver-polymer complex membranes

Silver ions dissolved in a polymer matrix are additionally coordinated by carbonyl oxygens of asparagines and their counter anions interact with cationic sites, resulting in the enhanced activity of the silver ion as an olefin carrier for facilitated olefin transport.     

Antibacterial activities of polystyrene-block-poly(4-vinyl pyridine) and poly(styrene-random-4-vinyl pyridine)

Styrene was polymerized in the presence of benzoyl peroxide (BPO) and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to yield polystyrene-TEMPO (PS-TEMPO) macroinitiator. The PS-TEMPO macroinitiator with different molecular weight was reacted with 4-vinyl pyridine (4-VP) to synthesize polystyrene-block-poly(4-vinyl pyridine) (PS-b-PVP), which was then quaternized with n-octyl iodide. Antibacterial activity of the quaternized copolymers was assessed against a gram negative bacterium (Pseudomonas aeruginosa) and a gram positive one (Staphylococcus aureus) by using the shake flask test method, and the results were compared with those of poly(styrene-random-4-vinyl pyridine) (P(ST-r--VP)). The quaternized copolymers inhibited greatly the growth of the bacteria, and PS-b-PVP was more active than P(ST-r-VP), which was ascribed to the fact that the content of quaternized 4-VP units on the surface of the particles of the former copolymer was higher than that corresponding to the latter one.     

Continuous flow and flow injection stripping voltammetric determination of silver(I), mercury(II), and bismuth(III) at a bulk modified graphite tube electrode

The epoxy-impregnated graphite tube electrode bulk modified with 2-mercaptobenzoxazole, employed in a wall-jet configuration, was found to be useful for the continuous flow and flow injection stripping voltammetric determinations of Ag^I, Hg^II and Bi^III. For continuous flow, detection limits for Ag^I, Hg^II and Bi^III were 1.8 × 10⁻¹⁰ M, 1.9 × 10⁻⁹ M and 9.5 × 10⁻⁹ M, respectively (10 min accumulation, S/N = 3). Precisions for 5.00 × 10⁻⁹ M Ag^I, 1.00 × 10⁻⁸ M Hg^II and 1.00 × 10⁻⁷ M Bi^III were 10.5%, 5.77 % and 7.90% (relative standard deviations, n = 6), respectively. In the case of flow injection stripping, with a 500 μL injection loop, detection limits of 0.59 ng, 2.0 ng and 120 ng were obtained for Ag^I, Hg^II and Bi^III, respectively (S/N = 3). Selected metal ions, inorganic and organic substances were investigated for interferences. The electrode was tested with a certified sample and then applied to the determinations of the metal ions in a urine and a sea-water sample.     

Construction of a 2,6-difunctionalized 2-methyl-2H-1-benzopyran library by using a solid-phase synthesis protocol

[reaction: see text] A library containing 1200 analogues of 2,6-difunctionalized 2-methyl-2H-1-benzopyran was constructed by using a solid-phase synthesis protocol. Polymer-bound 6-amido-, 6-sulfonamido-, and 6-uredo-functionalized 2-hydroxymethyl-2-methylbenzopyrans 10 were prepared as part of a first-generation diversification step by employing reactions of respective acid halides, sulfonyl chlorides, and isocyanates with the amine precursor 7. Transformations of the resin-bound intermediates 10 by reactions with alkyl and acid halides were then used to produce a diverse series of 2,6-difunctionalized 2-methyl-2H-1-benzopyran analogues 12 and 14.     

Differential effects of Fas cross-linking on phospholipase D activation and related lipid metabolism in Fas-resistant A20 cells

A20 murine lymphoma cells undergoing Fas-mediated apoptosis showed increase in the activity of phospholipase D (PLD), which is involved in proliferative or mitogenic cellular responses. Using A20 cell lines that were resistant to Fas-induced apoptosis, we investigated the differential effects of Fas cross-linking on PLD activity and sphingolipid metabolism. The basal PLD activities in all of the selected three Fas-resistant clones (#5, #8, and #11) were about 2~4 folds higher than that of wild type A20 cells. Among the PLD isoforms, PLD2 expression was increased in all of the selected Fas-resistant clones. The Fas downstream signaling events triggered by Fas cross-linking, including the activations of PLD, phosphatidylcholine-specific phospholipase C (PC-PLC), sphingomyelinase (SMase), the increase in diacylglycerol (DAG) and protein phosphorylation levels, and the translocation of protein kinase C to membrane were not changed in both of Fas-resistant clone #5 and #8. In contrast, Fas cross-linking stimulated the activity of PLD, PC-PLC, and SMase, translocation of PKC, and protein phosphorylation in Fas-resistant clone #11, similar to that of wild type cells. We also found that clone #11 had a different Fas sequence encoding Fas B which has been known to inhibit Fas-induced apoptosis. These findings suggest that increased PLD2 expression resulting in increased basal PLD activity and the blockade of Fas downstream signaling cascades may be involved to limit apoptosis induced by Fas cross-linking.     

Stereoselective synthesis of (+)-SCH 351448: a unique ligand system for sodium, calcium, and other cations

(+)-SCH 351448 (Na+ salt A) was synthesized employing ring-closing olefin metathesis reaction of an open diene diester intermediate for construction of the 28-membered macrodiolide structure. The open diene diester was prepared from the monomeric hydroxy carboxylic acid and two different olefin fragments. The monomeric hydroxy acid was synthesized via Julia-Julia coupling reaction of intermediates derived from the same olefinic fragments. Oxane units in these fragments were prepared by radical cyclization reactions of beta-alkoxyacrylates. Analogous SCH 351448 salts incorporating other mono- and divalent cations may be prepared. Under acidic conditions, SCH 351448 (Na+ salt A) was the most stable complex, but SCH 351448 (Ca2+ salt) and (Na+ salt B) appear to be physiologically important species.     

Mesocellular polymer foams with unprecedented uniform large mesopores and high surface areas

Mesocellular polymer foams with uniform approximately 17 nm cellular pores were fabricated using mesocellular silica foams as inorganic templates. The mesocellular polymer foams have high surface areas up to approximately 600 m(2)g(-1) and pore volumes of 1.6 cm(3)g(-1).