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The environmentally amiable route to carbon-heteroatom bond formation, described by Sharpless as 'click chemistry', has become known as a fast, efficient, and reliable approach to the synthesis of novel compounds with desired functionalities. Readily available starting materials must be used in this methodology and they should be essentially inert to most biological and organic conditions, including water and molecular oxygen. In this review, we cover reactions included in this label such as cycloadditions, nucleophilic ring-opening reactions of strained cycles, and amide synthesis, as well as their applications in organic synthesis, molecular biology, macromolecular chemistry and materials science. 1 Introduction 2 Click Synthesis of Epoxides and Aziridines 3 Nucleophilic Opening of Strained Rings: Epoxides and Aziridines 4 Huisgen 1,3-Dipolar Cycloadditions 4.1 Supramolecular Click Chemistry 4.2 Liquid Crystals 4.3 Self-Assembled Monolayers 4.4 Multicomponent Reactions 4.5 Creating Drug Candidates under Click Conditions 4.6 Click Chemistry with Peptides and Proteins 4.7 DNA as Participant in Click Reactions 5 Concluding Remarks

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The effect of conformation on glycoside reactivity was investigated by studying the hydrolysis of a selection of 3,6-anhydroglucosides as models for glucose in the highly reactive (1)C(4) conformation. Methyl 3,6-anhydro-beta-D-glucopyranoside was found to hydrolyze 200-400 times faster than methyl glucosides in the (4)C(1) conformation, while methyl 3,6-anhydro-beta-D-galactopyranoside, which is in the B(1,4) conformation, was less reactive than methyl beta-D-galactopyranoside. Methyl (3,6-anhydro-beta-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranoside, methyl (3,6-anhydro-alpha-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranosyl-(1 --> 6)-alpha-D-glucopyranoside, and methyl (3,6-anhydro-beta-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranosyl-(1 --> 6)-alpha-D-glucopyranoside were prepared and found to react selectively at the anhydro residue. The finding that (1)C(4) conformers of glucosides are highly reactive species is in accordance with and supports previous results showing that axial OH groups are less electron withdrawing than equatorial OH groups.