In 1985, Houghten  reported on peptide synthesis carried out on a resin sealed in porous polypropylene packets. The pore size of the polypropylene mesh (74 mm) allows the free access of chemicals to and from the contained resin. Each packet or ''tea-bag'' can be individually labeled to identify the peptide synthesized on the entrapped polymer. Many ''tea-bags'' can be combined in the same reaction to carry out common synthetic steps, such as washing and deprotection. The packets are sorted in separate reaction vessels according to the specific amino acid that will be coupled next. Cleavage, depending on the amount of used resin, can be carried out in separate vessels or in a 96-well microtiter plate with a 2-mL well volume. In the original paper, 248 different tridecapeptides were synthesized in 10- to 20-mg quantities and characterized in less than 4 weeks.
The ''tea-bag'' method is very practical as it does not require any special tools, except a sealing device to make the ''tea-bags''. A number of mesh materials of different porosity are available form Spectrum Medical Industries. Almost all commercially available resins can be used, as long as the size of the beads is larger than the mesh size; in addition, the mesh should be stable to reaction conditions. The scale of the synthesis is easy to control by the size of the packet chosen to contain the desired amount of a polymer support. Multiple synthesis can be carried out manually or on a synthesizer. The ''tea-bags'' can be mechanically labeled, or radiofrequency tags can be used for this purpose.
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