ABSTRACT
The limitations of linear “solitary” peptide synthesis were first overcome by Houghten [25] with the use of tea-bag methodology and Geysen with “pin” methodology [26]. The pin method was a revolutionary approach to peptide synthesis and moved away from traditional PS-based resins, allowing the synthesis of peptides on the surface of polyethylene (PE) supports [rod-like materials termed pins (4 mm diameter×40 mm)] in a multiple parallel manner. These derivatized materials were prepared by radiation grafting in which the pins were placed in a γ-radiation source in the presence of an aqueous solution of acrylic acid. Radiation (initially 1 million rad) activated the surface by radical formation to a depth of several micrometers, which reacted with the acrylic acid to give rise to a polyacrylic
acid derivatized pin (Fig. 7). It was this (immobilized) graft that could then be used as a support for peptide synthesis, initially by coupling to a suitably protected lysine residue (Boc-Lys-OMe). Due to the discrete and handlable nature of the pins they could be
arranged in an array format akin to the microtiter plates used for biological screening with synthesis taking place by dipping the tips of the pins into the appropriate solutions. Although the whole pin was derivatized, only the tip was actually used synthetically. The major problems were thus logistical, due to compound numbers, rather than chemical. This basic procedure allowed the synthesis in 1984 of 208 overlapping peptides covering the entire peptide sequence of the coat protein VP1 of foot-and-mouth disease virus (FMDV). This was accomplished using Boc chemistry with the peptide directly attached to the pin as shown in Figure 7. Two assumptions made by the authors in this original work were that an initial loading of at least 1 nmol would be sufficient for even a lowefficiency synthesis to allow antibody binding and that high purity was not necessary.
