Rigid spacers: Optimal highly potent divalent ligands of the P. aeruginosa lectin LecA have been prepared. The ligands consist of a rigid spacer derived from glucose–triazole units (see figure). Systematic variation of the number of spacer units and the aglycon linker led to a 7500‐fold enhancement in potency.

Multivalent galactosides inhibiting Pseudomonas aeruginosa biofilms may help control this problematic pathogen. To understand the binding mode of tetravalent glycopeptide dendrimer GalAG2 [(Gal-β-OC6H4CO-Lys-Pro-Leu)4(Lys-Phe-Lys-Ile)2Lys-His-Ile-NH2] to its target lectin LecA, crystal structures of LecA complexes with divalent analog GalAG1 [(Gal-β-OC6H4CO-Lys-Pro-Leu)2Lys-Phe-Lys-Ile-NH2] and related glucose-triazole linked bis-galactosides 3u3 [Gal-β-O(CH2)n-(C2HN3)-4-Glc-β-(C2HN3)-[β-Glc-4-(N3HC2)]2-(CH2)n-O-β-Gal (n = 1)] and 5u3 (n = 3) were obtained, revealing a chelate bound 3u3, cross-linked 5u3, and monovalently bound GalAG1. Nevertheless, a chelate bound model better explaining their strong LecA binding and the absence of lectin aggregation was obtained by modeling for all three ligands. A model of the chelate bound GalAG2·LecA complex was also obtained rationalizing its unusually tight LecA binding (KD = 2.5 nM) and aggregation by lectin cross-linking. The very weak biofilm inhibition with divalent LecA inhibitors suggests that lectin aggregation is necessary for biofilm inhibition by GalAG2, pointing to multivalent glycoclusters as a unique opportunity to control P. aeruginosa biofilms.

The synthesis of a new rigid spacer based on carbohydrate-triazole repeating units and their incorporation into divalent systems is described. Inhibition studies showed that a well-matched system with a rigid spacer with flexible ends leads to the most potent inhibition of Pseudomonas aeruginosa lectin LecA.

SummaryThe synthesis of phenylene-ethynylene rods and their use as rigid spacers is described. Alternation of a Sonogashira reaction and silyl group cleavage was used to obtain rigid spacers with even and odd numbers of phenylene units. Preliminary applications of these rods in divalent systems are shown. Inhibition studies with Pseudomonas Aeruginosa lectin LecA showed that the rigid spacer proved greatly beneficial for the inhibitory potency.

Acetylated/silylated maltooligosaccharides with different degrees of oligomerization have been tested as chiral stationary phases for enantioselective gas chromatography. The acyclic dextrin derivatives carrying tert-butyldimethylsilyl groups at the primary hydroxyl sites and acetyl groups at the secondary hydroxyl sites showed an unexpected ability for the enantioseparation of alpha-amino acid derivatives and halogenated compounds, in addition to some underivatized chiral compounds. Some examples of an improved enantioselectivity invoked by the linear CSPs as compared to that of cyclic oligosaccharides are demonstrated in this work. The results highlight the role of the polar external surface of the selector in lieu of the well-established inclusion mechanism of enantiorecognition by cyclic dextrins. Thus, the enantioseparation of chiral compounds on linear dextrin derivatives--devoid of a molecular cavity--sheds a new light on the mechanisms of enantiorecognition by cyclodextrin derivatives. In contrast to cyclodextrins, linear dextrins are readily accessible in both enantiomeric forms.

NMR spectroscopic investigations involving extensive use of ROESY and DOSY techniques and comparison withsilylated‐acetylated linear dextrins as acyclic model compounds shed light on the origin of the phenomenon ofenantiodiscrimination of fluorinated α‐amino acid derivatives by heptakis[2,3‐di‐O‐acetyl‐6‐O‐(tert‐butyldimethylsilyl)]‐β‐cyclodextrin. The effectiveness and versatility of the cyclic derivatized oligosaccharide as a chiral solvating agent for the NMR determination of enantiomeric purity in the same class of compounds is demonstrated. A regular correlation between the relative positions of enantiomers' signals and absolute configurations is observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Amino acids U 0400 External vs. Internal Interactions in the Enantiodiscrimination of Fluorinated α-Amino Acid Derivatives by Heptakis[2,3-di-O-acetyl-6-O-(tert-butyldimethylsilyl)]-βcyclodextrin, a Powerful Chiral Solvating Agent for NMRSpectroscopy. -(UCCELLO-BARRETTA*, G.; BALZANO, F.; PERTICI, F.; JICSINSZKY, L.; SICOLI, G.; SCHURIG, V.; Eur.