In this group of the universal supports, the hydroxy groups are protected with the 1-methoxy -1-ethylidene (MED) group. In contrast to the conventional DMT group, no colorful product is formed in the course of deprotection. The treatment with an acid results in the hydrolysis of the orthoester to deprotect one of the hydroxy groups while the other one is left protected as an acetate ester. The MED protecting group is completely removed by treating the solid support for 20 s with 3% dichloroacetic acid or 2% trichloroacetic acid in methylene chloride so that carrying out the standard detritylation subroutine is more than sufficient for the deprotection of the solid support.
There are two types of universal solid supports different in the attachment of the universal linker to the solid phase.
In the first type, the universal linker is attached via a cleavable ester bond of succinyl linker. These supports (products 01111-01113) are perfect for small-scale applications including the synthesis in 96-well plates. When the final deprotection is carried out, the oligonucleotides are first released from the solid phase. With ammonia-methylamine mixture (AMA) and concentrated aqueous ammonium hydroxide at room temperature, this step requires 15 min and 1 h, respectively. The dephosphorylation and the base deprotection are then carried out in solution. In this case, dephosphorylation of P=O 2’-deoxyoligonucleotides with AMA and conc. aqueous ammonium hydroxide requires 1 h and 8 h at 65°C, respectively. With gaseous ammonia, following the standard protocol for the deprotection of nucleic bases is sufficient for the completion of the 3'- dephosphorylation. With 2'-O-substituted nucleosides, the dephosphorylation is more rapid. Importantly, the dephosphorylation of the 3'-terminus is more rapid than the deprotection of nucleic bases even when the labile base-protecting groups are used.
In the second type of solid supports (items 01121-01123), the universal linker is attached to the solid phase via a chemically inert amide bond. In the final deprotection step, the solid phase should be kept in contact with the deprotecting agent over a period of time sufficient to complete the 3'-dephosphorylation (see above). These supports are most suitable for large-scale applications where the time of exposure of the solid phase to concentrated aqueous ammonium hydroxide is less critical.
To read and download the User Guide for Universal Solid Supports, use this link.