Split and mix protocols

While the procedure shown in Scheme 4 [26], Hke the original method, introduces much of the diversity (i. e., up to three variable positions) off the solid phase, thereby limiting the combinatorial potential available for split-and-mix protocols, another recently described scheme [30] builds up the diversity in a stepwise manner on the solid phase, which simpHfies the logistics for automated library production. Intermediates may also be used to access thiohydantoins (see Scheme 6). 

This dendritic support (1) was used to generate a library of indole derivatives with three centers of diversity following the Fischer protocol and the split and mix strategy. One example of this sequence is outlined in Scheme 7.1. 

The library of 140 pyrrole-3-carboxamides was synthesized following the split-mix protocol with 14 primary amines and 10 a-bromo-ketones as variable building blocks. In the first step Rink-Amide-AM-PS resin was acetoacetylated at —15 °C by addition of di-ketene to the resin suspended in CH2CI2. After 0.5 h at —15 °C and 2 h at room temperature the resin was washed and dried. A negative Kaiser test proved the complete conver-... 

Split synthesis is a completely different approach to library generation from parallel synthesis. Furthermore, split synthesis can be performed only on a resin solution phase is not an option. Split synthesis involves dividing, or splitting, a pile of loaded resin into batches for reaction with a set of building blocks. After the reaction, all the resin is pooled back together, thoroughly mixed, and then resplit for reaction with the next set of building blocks. Based on this protocol, split synthesis is often also called mix-split or pool-split synthesis. 

The feasibility of on-bead screening of an SP tweezer library with soluble tripeptides was then evaluated. An 125-member SPpool library L36 was prepared (Fig. 9.51) from the key resin-bound intermediate 9.137 using mix-and-split protocols, three monomer sets M1-M3, each containing five a-amino acid representatives, and the... 

Francis et al. (227) reported the synthesis of a > 10,000-member encoded SP pool library L37 characterized by a turn element (monomers M2, prepared using simple synthetic routes) surrounded by two a-amino acids (monomers Mi and M3) and capped on the N-terminus (monomers M4). The structure of the library and the monomer sets are reported in Fig. 9.52. Mix-and-split protocols and a popular encoding method (177) were used to prepare and encode the library. 

Split the purified cDNA from step 10 into two samples of 25 pL each. Mix each sample with 10 pL of the appropriate lOx reaction buffer (provided by the supplier) and bring to a total volume of 100 pL with water. Add 10 U of either of two restriction enzymes (Nla III or Tai 7 see Note 5) and incubate at the appropriate temperature (37 °C for Nla III, 65 °C for Tai I) for 1 h. Recover the digested cDNA using the QIAquick PCR Purification Kit, following the manufaaurer s protocol to the letter. Elute the cDNA in 50 pL of the included elution buffer (EB). 

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