Fluorous benzyl group

The assembly of tetrapeptide 19 that contains all possible 0-dipeptide bonds, (03-03)-, (03-02)-, and (02-03), and also a turn inducing 03-(R)-Ala-02-(R)-Val element was achieved employing a Boc-strategy (Scheme 5). A fluorous benzyl group was incorporated in the first amino acid to streamline the purification procedure by fluorous solid phase extraction (LSPE) (Lilippov et al. 2002 de Visser et al. 2003). Thus, the assembly of the fully protected tetrapeptide commenced with the construction of the first 03-03-peptide bond by applying the previously established conditions. A residence time of 3 min at 90°C provided the Boc-protected dipeptide 15 in 91% isolated yield after LSPE. Notably, the product precipitated in the collection flask, which was kept at ambient temperature, indicating the poor solubility of this class of compounds (Hessel et al. 2005). 

Figure 10. Disaccharide synthesis with a fluorous benzyl group...

Scheme 3.18 Synthesis (box) and use of a fluorous benzyl protective group...

A recent example of the parallel synthesis of different quinazoline-2,4-dione derivatives (46) demonstrates how to combine the advantages of fluorous synthesis with those of solid-phase chemistry without using expensive perfluorinated solvents [22] (Scheme 3.22). In the beginning, a fluorous benzyl alcohol (47) is adsorbed on fluorous reversed-phase silica gel (FRPSG). Then, in a sequence of splits and reactions, the linker group, which remains bound to the FRPSG by fluorophilic interactions, is converted into a library of differently substituted carboxamido-urethanes (48). These are cyclized and the liberated quinazoline-2,4-diones (46) are eluted from the support with the fluorophobic solvents water and CHjCN/... 

Curran, DP, Feiritto R, Hua Y. Preparation of a fluorous benzyl protecting group and its use in fiuorous synthesis approach to a disaccharide. Tetrahedron Lett. 1998 39 4937 940. 

D. P. Curran, R. Ferritto, Y. Hua, Preparation of a Eluor-ous Benzyl Protecting Group and its Use in a Fluorous Synthesis Approach to a Disaccharide , Tetmzhedron Lett. 1998, 39, 4937. 

The synthesis of N-alkylated dihydropteridinones 34 started with a displacement reaction of 4,6-dichloro-5-nitropyrimidine with a fluorous amino-ester (Scheme 23) [53]. The compounds formed 35 were then reacted with secondary amines to yield 36. The reduction of the nitro group of 36 was conducted by hydrogenation using Pd on charcoal as a catalyst. The cyclization reactions of 37 were promoted by microwave irradiation. The N-alkylation reaction of the cyclized products 38 with benzyl halides gave monobenzylated... 

Oligosaccharide syntheses have also been performed in parallel using a fluorous support.A benzyl-type protecting group (HfBn) used in some of these procedures is shown in Figure 7.26. The novel approach here is that the fluorous group or tag is recycled and this can be achieved fairly easily... 

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