The Chirality of Aggregated Yariv Reagents Correlates with Their AGP-Binding Ability.

Yariv reagents are glycosylated triphenylazo dyes that bind to arabinogalactan proteins (AGPs), proteoglycans found in plant cell walls that are integral for plant growth and development. Yariv reagents are widely utilized as imaging, purification, and quantification tools for AGPs and represent the only small molecule probe for interrogating AGP function. The ability of Yariv reagents to bind to AGPs is dependent on the structure of the terminal glycoside on the dye. The reason for this selectivity has not been understood until the present work. Using circular dichroism spectroscopy, we show that the Yariv reagents form supramolecular aggregates with helical chirality. More significantly, the ability of the Yariv reagent to bind AGPs is correlated with this helical chirality. This finding paves the way towards developing a more detailed understanding of the nature of the Yariv-AGP complex, and the design of AGP-binding reagents with higher affinities and selectivities.

Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies.

The silylated hexatriynyl complex trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)3 SiEt3 (PtC6 TES) is converted in situ to PtC6 H (wet n-Bu4 N+ F- , THF) and cross coupled with the diyne H(C≡C)2 SiEt3 (HC4 TES; CuCl/TMEDA, O2 ) to give PtC10 TES (71 %). This sequence is repeated twice to afford PtC14 TES (65 %) and then PtC18 TES (27 %). An analogous series of reactions starting with PtC8 TES gives PtC12 TES (60 %), then PtC16 TES (43 %), and then PtC20 TES (17 %). Similar cross couplings with H(C≡C)2 Si(i-Pr)3 (HC4 TIPS) give PtC12 TIPS (68 %), PtC14 TIPS (68 %), and PtC16 TIPS (34 %). The trialkylsilyl species (up to PtC18 TES) are converted to 3+2 "click" cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n-1 C=CHN(CH2 C6 H5 )N=N (29-92 % after workups). The most general procedure involves generating the terminal polyynes PtCx H (wet n-Bu4 N+ F- , THF) in the presence of benzyl azide in DMF and aqueous CuSO4 /ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC20 TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.

An Improved Protocol for the Synthesis and Purification of Yariv Reagents.

Yariv reagents are glycoconjugate tris-azo dyes widely used in plant biology. These reagents are synthesized by diazo coupling between phloroglucinol and a para-diazophenyl glycoside. Despite their synthetic accessibility, well-defined protocols for obtaining pure Yariv reagents, and their complete compound characterization data, have not been reported. We report here optimized protocols used to synthesize, purify, and characterize a panel of six Yariv reagents and suggest approaches that could be valuable for the purification and characterization of other glycoconjugates as well.

Anti-bacterial glycosyl triazoles - Identification of an N-acetylglucosamine derivative with bacteriostatic activity against Bacillus.

N-acetylglucosaminidases (GlcNAcases) play an important role in the remodeling and recycling of bacterial peptidoglycan. Inhibitors of bacterial GlcNAcases can serve as antibacterial agents and provide an opportunity for the development of new antibiotics. We report the synthesis of triazole derivatives of N-acetylglucosamine using a copper promoted azide-alkyne coupling reaction between 1-azido-N-acetylglucosamine and a small library of terminal alkynes prepared via the Ugi reaction. These compounds were evaluated for their ability to inhibit the growth of bacteria. Two compounds that show bacteriostatic activity against Bacillus were identified, with MIC values of approximately 60 µM in both cases. Bacillus subtilis cultured in the presence of sub-MIC amounts of the glycosyl triazole inhibitors exhibit an elongated phenotype characteristic of impaired cell division. This represents the first report of inhibitors of bacterial cell wall GlcNAcases that demonstrate inhibition of cell growth in whole cell assays.