Approach Toward a Generic Treatment of Gram-Negative Infections: Synthesis of Haptens for Catalytic Antibody Mediated Cleavage of the Interglycosidic Bond in Lipid A

Amino-functionalized iminocyclitols: synthetic glycomimetics of medicinal interest

A review on the syntheses and biological activities of unnatural glycomimetics highlighting the effect of replacement of hydroxyl groups of natural iminosugars by amino functionalities is presented.

Photo-click chemistry strategies for spatiotemporal control of metal-free ligation, labeling, and surface derivatization

Three photo-click ligation strategies described in this account provide scientists with efficient and selective tools for derivatization of various molecules, polymers, and surfaces. Fast photochemical reactions that are utilized in these techniques permit spatiotemporal control of the process. The absence of activating reagents and catalysts, as well as compatibility with aqueous media, makes photo-click ligations suitable for biomedical applications. The first of these approaches relies on the photochemical decarbonylation of cyclopropenones to produce cyclooctynes. The latter undergo rapid catalyst-free strain-promoted azide–alkyne cycloaddition (SPAAC) to azide-tagged substrates. The second method is based on a very fast (>104 M–1 s–1) light-triggered hetero-Diels–Alder reaction and permits efficient derivatization of substrates bearing vinyl ether moiety. An even faster reaction between photochemically generated naphthoquinone methides (oNQMs) and thiols (~2 × 105 M–1 s–1) serves as a basis for a third method. This thiol photo-click chemistry allows for the selective derivatization of thiol-functionalized substrates or labeling of free cysteine residues in proteins. The thioether linkage produced by the reaction of oNQMs and a thiol is stable under ambient conditions, but can be cleaved by UV irradiation, regenerating free thiol. This feature permits the removal or replacement of immobilized compounds, as well as traceless substrate release.

Inhibitors for Bacterial Cell-Wall Recycling

Gram-negative bacteria have evolved an elaborate process for the recycling of their cell wall, which is initiated in the periplasmic space by the action of lytic transglycosylases. The product of this reaction, β-D-N-acetylglucosamine-(1→4)-1,6-anhydro-β-D-N-acetylmuramyl-L-Ala-γ-D-Glu-meso-DAP-D-Ala-D-Ala (compound 1), is internalized to begin the recycling events within the cytoplasm. The first step in the cytoplasmic recycling is catalyzed by the NagZ glycosylase, which cleaves in a hydrolytic reaction the N-acetylglucosamine glycosidic bond of metabolite 1. The reactions catalyzed by both the lytic glycosylases and NagZ are believed to involve oxocarbenium transition species. We describe herein the synthesis and evaluation of four iminosaccharides as possible mimetics of the oxocarbenium species, and disclose one as a potent (compound 3, K(i) = 300 ± 15 nM) competitive inhibitor of NagZ.

Patterned surface derivatization using Diels-Alder photoclick reaction

The utility of photochemically induced hetero-Diels-Alder reaction for the light-directed surface derivatization and patterning was demonstrated. Glass slides functionalized with vinyl ether moieties are covered with aqueous solution of substrates conjugated to 3-(hydroxymethyl)-2-naphthol (NQMP). Subsequent irradiation via shadow mask results in an efficient conversion of the latter functionality into reactive 2-napthoquinone-3-methide (oNQM) in the exposed areas. oNQM undergoes very facile hetero Diels-Alder addition (k(D-A) ≈ 4 × 10(4) M(-1)s(-1)) to immobilized vinyl ether molecules resulting in a photochemically stable covalent link between a substrate and a surface. Unreacted oNQM groups are rapidly hydrated to regenerate NQMP. The click chemistry based on the addition of photochemically generated oNQM to vinyl ether works well in aqueous solution, proceeds at high rate under ambient conditions, and does not require catalyst or additional reagents. This photoclick strategy represents an unusual paradigm in photopatterning: the surface itself is photochemically inert, while photoreactive component is present in the solution. The short lifetime (τ ≈ 7 ms in H(2)O) of the active form of a photoclick reagent in aqueous solution prevents its migration from the site of irradiation, thus allowing for the spatial control of surface derivatization. Both o-napthoquinone methide precursors and vinyl ethers are stable in dark and the reaction is orthogonal to other derivatization techniques, such as acetylene-azide click reaction.

Light-induced hetero-Diels-Alder cycloaddition: a facile and selective photoclick reaction

2-Napthoquinone-3-methides (oNQMs) generated by efficient photodehydration (Φ=0.2) of 3-(hydroxymethyl)-2-naphthol undergo facile hetero-Diels-Alder addition (k(D-A)∼ 4×10(4) M(-1) s(-1)) to electron-rich polarized olefins in an aqueous solution. The resulting photostable benzo[g]chromans are produced in high to quantitative yield. The unreacted oNQM is rapidly hydrated (k(H2O) ∼145 s(-1)) to regenerate the starting diol. This competition between hydration and cycloaddition makes oNQMs highly selective, since only vinyl ethers and enamines are reactive enough to form the Diels-Alder adduct in an aqueous solution; no cycloaddition was observed with other types of alkenes. To achieve photolabeling or photoligation of two substrates, one is derivatized with a vinyl ether moiety, while 3-(hydroxymethyl)-2-naphthol is attached to the other via an appropriate linker. The light-induced Diels-Alder "click" strategy permits the formation of either a permanent or hydrolytically labile linkage. Rapid kinetics of this photoclick reaction (k=4×10(4) M(-1) s(-1)) is useful for time-resolved applications. The short lifetime (τ ∼7 ms in H(2)O) of the active form of the photoclick reagent prevents its migration from the site of irradiation, thus, allowing for spatial control of the ligation or labeling.

Design and synthesis of 2-acetamidomethyl derivatives of isofagomine as potential inhibitors of human lysosomal β-hexosaminidases

As part of a program towards the development of specific inhibitors of human lysosomal beta-hexosaminidase for use as chemical chaperones in therapy of G(M2) gangliosidosis related diseases, the synthesis of 2-acetamidomethyl derivatives of isofagomine has been undertaken. Key event in this synthesis is the conversion of a C-2 substituted gluconolactone derivative into the corresponding lactam, followed by reduction to the corresponding amine. The 1-N-imino-2 acetamidomethyl derivative 5 proved to be a rather selective inhibitor with a K(i) of 2.4 microM for homogenate of human spleen lysosomal beta-hexosaminidase.

Polyhydroxylated alkaloids -- natural occurrence and therapeutic applications

Over one hundred polyhydroxylated alkaloids have been isolated from plants and micro-organisms. These alkaloids can be potent and highly selective glycosidase inhibitors and are arousing great interest as tools to study cellular recognition and as potential therapeutic agents. However, only three of the natural products so far have been widely studied for therapeutic potential due largely to the limited commercial availability of the other compounds.