What does the word 'click' mean here? I guess it means "join" here but I'm not sure.
Yes, it is detailed here and in numerous other places. It refers to a class of reactions, and does not mean "join."
From the above-cited page on named reactions:
"Click Chemistry" is a term that was introduced by K. B. Sharpless in 2001 to describe reactions that are high yielding, wide in scope, create only byproducts that can be removed without chromatography, are stereospecific, simple to perform, and can be conducted in easily removable or benign solvents.
Sigma-Aldrich has a primer where they state:
The traditional process of drug discovery based on natural secondary metabolites has often been slow, costly, and labor-intensive. Even with the advent of combinatorial chemistry and high-throughput screening in the past two decades, the generation of leads is dependent on the reliability of the individual reactions to construct the new molecular framework. Click chemistry is a newer approach to the synthesis of drug-like molecules that can accelerate the drug discovery process by utilizing a few practical and reliable reactions. Sharpless and coworkers defined what makes a click reaction as one that is wide in scope and easy to perform, uses only readily available reagents, and is insensitive to oxygen and water. In fact, in several instances water is the ideal reaction solvent, providing the best yields and highest rates. Reaction work-up and purification uses benign solvents and avoids chromatography.
A pretty comprehensive overview is given here, in a manuscript entitled Click Chemistry, a Powerful Tool for Pharmaceutical Sciences. Hein, Liu, and Wang. Pharm Res. 2008 Oct; 25(10): 2216–2230.
Click chemistry is a term coined by K.B. Sharpless in 2001. The original paper "Click Chemistry: Diverse Chemical Function from a Few Good Reactions." describes a set of very well working reactions with certain characteristics that, in general, can be used to join molecules together. Such characteristics are for example:
- wide in scope
- high rates and yields
- very selective
- no/ inoffensive byproducts
- ideally work in water
This was the original definition, however, if people talk about click chemistry nowadays what they often refer to is the copper catalyzed Alkyne Azide Cycloaddition or similar reactions like the Strain-Promoted Alkyne Azide Cycloaddition (copper-free click chemistry) or the Tetrazine Ligations.
- Hartmuth C. Kolb, M. G. Finn, K. Barry Sharpless, Angew. Chem. Int. Ed. 2001, 40 (11), 2004-2021. DOI: 10.1002/1521-3773(20010601)40:11<2004::AID-ANIE2004>3.0.CO;2-5
- Christian Spiteri, John E. Moses, Angew. Chem. Int. Ed. 2009, 49 (1), 31-33. DOI: 10.1002/anie.200905322
- Jan Dommerholt, Floris P. J. T. Rutjes, Floris L. van Delft, Topics in Current Chemistry, 2016, 374, 16. DOI: 10.1007/s41061-016-0016-4
- Jolita Šečkutė, Neal K Devaraj, Curr. Opin. Chem. Biol., 2013, 17, 761 - 767. DOI: 10.1016/j.cbpa.2013.08.004