CPG support

Iadonisi s group reported the preparation of an amino CPG support (30-35 Tmol NH2/g) of P-(l—>6)-linked glucose dimer (Scheme 4.14).16... 

Scheme 4.12 Application of CPG support in solid-phase oligosaccharide synthesis using glycosyl trichloroacetimidates.

Scheme 4.14 Preparation of an amino CPG support of P-(l —>6)-linked glucose dimer.

An ester bond is widely used, and the succinate 2.29 (91) is one of the most popular linkers. It is introduced onto the LCAA-CPG support as the 3 -monosuccinate ester of the first nucleoside, and it is cleaved under basic conditions in the final SPS step. The inclusion of a sarcosine spacer as in 2.30 (92) increases the linker stability... 

The SP assembly of the ON 15-mer was performed on a l- J,mol scale using an automated synthesizer. The succinate was coupled to the LCAA-CPG support (500 A) to give 2.73 (Fig. 2.21), which was submitted to reaction cycles for each elongation. The first elongation cycle is shown in detail in Fig. 2.21 and begins with detritylation of the resin-bound intermediate (step a) followed by a washing step (step b). Coupling... 

Diacid-based linkers, such as the succinic linker 21, have been described to prepare alcohols. The procedure involves the esterification of the starting alcohol with succinic anhydride and DMAP to yield the hemiester that is anchored to an amino containing-resin by means of an amide bond. The bound alcohol is then elaborated and finally released with a nucleophile. Oligosaccharides have been assembled following this approach and released with aqueous ammonia or sodium methoxide in methanol-dioxane [73, 74]. Peptide alcohols have also been prepared with the succinic linker on BHA resin and released by treatment with NH3 in MeOH for 72-96h or hydrazine in DMF for 24h [75]. Similarly, hydroquinone-0,0 -diacetic acid (linker 22) has been used to link nucleosides to polystyrene or CPG supports. Cleavage of oligonucleotides was carried out with aqueous ammonia [76]. Other diacids with a similar function have also been described [77]. 

Following the success of NPE/NPEOC chemistry [214], Eritja et al. [233] have developed an NPE linker to CPG support based on 4-(2-hydroxyethyl)-3-nitroben-... 

The P-eliminable NPE anchor (Figure 19.10) has also been proposed by Eritja et al. [233] for the synthesis of 3 -phosphates by the phosphoramidite method on LCAA-CPG support (Section 19.3.1.3). 

A urethane linker, 40, was introduced by Sproat and Brown [109] as an alternative to the succinyl linkage and is prepared by reacting LCAA-CPG with tolylene-2,6-diisocyanate. A 19-mer oligonucleotide constructed on this urethane-linked CPG support was successfully deprotected by extended aqueous ammonia treatment at 56°C for 48 h. 

Photolabile CPG supports, based on the ort/io-nitrobenzyl moiety, have been designed by Greenberg et al. [118,119] to provide orthogonal oligonucleotide cleavage conditions suitable for alkali-sensitive oligonucleotides. 

Pon RT, Yu S, Guo Z, Sanghvi Y. Multiple oligodeoxynucleotide syntheses on a reusable solid-phase CPG support via the hydroquinone-0,0 -diacetic acid (Q-linker) linker arm. Nucleic Acids Res 27 1531-1538, 1999. 

Another important feature of the synthesis of oligonucleotide-peptide conjugates is the choice of a solid support. Polystyrene supports are used in peptide synthesis and CPG supports are incorporated for oligonucleotide synthesis. Most reports describe the use of CPG for the synthesis of oligonucleotide-peptide conjugates [13,14,26,27,36,63,74]. However, in some cases low coupling yields have been reported with CPG and alternative supports have been described, such as Teflon [34], polystyrene (PS)... 

Preparation of supported copper catalysts. Two different supports were used to prepare supported catalysts. Silica gel with specific surface area of 200 m /g, pore volume of 1.5 cm /g, and particle size of 0.02-0.20 mm was used without any further treatment. The controlled pore glass (CPG) support (particle size 0.045-0.10 mm) was prepared as described elsewhere [4,5]. CPG support with surface area of 33 m /g, pore size 75 nm, pore volume 0.59 cm /g was used. The catalysts were prepared by incipient wetness impregnation of the support with Cu(ll) nitrate in the presence of citric acid followed by drying in air at 230 °C. The dried samples were calcined at 500 °C for 5 hours followed by reduction in a hydrogen atmosphere at 300-400 °C. 

Resuits obtained over siiica and CPG supported cataiysts are aiso included into Tabie 1. Siiica supported catalysts showed moderate activity. Over these catalysts the M/S ratio was beiow 2, i.e. the enantioselectivity of siiica supported copper catalysts was not better than that of the Raney-copper catalysts. 

The activity of CPG supported cataiysts was slightiy lower than that of the silica supported catalysts, however, the D-mannitol selectivity showed the highest value. Over these catalysts in the absence of additives M/S ratios above 4, or D-mannitol selectivity values around 80 % could be obtained. 

By using sodium haiides or sodium borate the hydrogenation of D-fructose could be carried out almost to the completion. These results are shown in Table 3. In these experiments upon using Raney-copper catalysts the highest selectivity of D-mannitol, 82.7 %, was obsen/ed over a cobalt containing catalysts in the presence of sodium borate. Even higher D-mannitol selectivity, i.e. 88.2, was observed over CPG supported copper catalyst in the presence of sodium borate. 

The high D-mannitol selectivity obtained over CPG supported copper catalysts needs further discussion. It is known that the surface of CPG is enriched with B-OH and B-(OH)2 moieties in the SiO matrix [8]. We suggest that the above surface moieties are involved in the overall selectivity control, if in the borate-substrate adduct the beta furanose form of the carbohydrate determines the enantio-differentiation step in the formation of D-mannitol [2], then due to the presence of surface B-(OH)2 moieties the concentration of the beta-furanose form of the carbohydrate should also increase resulting in the high selectivity for the formation of D-mannitol. 

Once all the nucleosides are in place and the last DMT is removed, treatment with aqueous ammonia removes the acyl and cyanoethyl groups and cleaves the oligonucleotide from the CPG support. 

In the case of DNA synthesis controlled-pore-glass (CPG) supports have become the favoured solid phase medium [8] and this raises the question of polymer versus inorganic support . In reality there is no real competition here, although would-be users have the opportunity to examine each option and select the one most suitable for their own needs. In fact, in many respects the two classes of support are complementary and offer different possibilities to potential users. For example, a transition metal complex immobilised on an inorganic support will find itself in quite a different electronic environment than the same complex immobilised on a polymer. Hence the immobilised complexes are in fact likely to be different and therefore to behave differently in catalytic applications. 

Convert the 5 -0-dimethoxytrityl base-protected 2 -(9-allylribo-nucleosides (generally 2 nunol) into their 3 -<7-succinates, and then turn these into the reactive 4-nitrophenyl esters. Subsequently react these with aminopropyl controlled pore glass (500 A pore diameter) to give the functionalized CPG supports for solid-phase synthesis. Use the identical procedure as described in detail for the 2 -0-methyl compounds (15). 

Automated Synthesis on 1- and 200- jmol Scales Using Controlled Pore Glass (CPG) Support, P-Cyanoethyl Diisopropyl Phosphoramidite (CED) Chemistry, and Tetraethylthiuram Disulfide (TETD)... 

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