(3 R

The title compound, C15H20N2O5, is the first example of a branched tetrahydro­furan sugar amino acid dipeptide isostere incorporated into a peptidomimetic. The crystal structure contains intermolecular N—H⋯O and O—H⋯O hydrogen bonds.


Comment
-Tetrahydrofuran (THF) sugar amino acids (SAA) have been extensively investigated as dipeptide isosteres (Baron et al., 2004;Grotenberg et al., 2004;Raunkjr et al., 2004).Introduction of -THF SAA building blocks has been shown to induce secondary structural features such as -turn-like structures (Chakraborty et al., 2004;Smith et al., 2003;Hungerford et al., 2000) and helices (Claridge et al., 1999;Osterkamp et al., 2000) in small peptidomimetics.All the previously reported -THF SAA scaffolds have linear carbon chains, as in (1), which has been incorporated into peptidomimetics such as (2).The synthesis of branched sugar lactones (Hotchkiss et al., 2004) has allowed ready access to a new class of -THF SAA building blocks, such as (3), which contain a branched carbon chain.The monomer (3) was prepared as an oil from l-lyxonolactone in a sequence in which the branched carbon chain was introduced by the Ho (1978, 1985a,b) crossed aldol procedure, and the -THF ring was subsequently formed by an intramolecular alkylation.The branched scaffold (3) was transformed into the crystalline branched peptidomimetic (4).
The structure of (4) has been determined in order to remove any ambiguity in the stereochemical outcomes of either the aldol or the ring closure reactions.Additionally, the crystal structure of (4) may give some indication of the

Figure 1
The molecular structure of (4), with displacement ellipsoids drawn at the 50% probability level.secondary structural motif likely to be induced by the incorporation of the monomer (3) into peptidomimetics.The molecular structure of (4) is shown in Fig. 1.As usually expected for sugar derivatives, there are intermolecular hydrogen bonds (Table 2 and Fig. 2).

Experimental
Compound (4) was dissolved in acetone in a small glass cylinder and then crystallized as the solvent evaporated slowly to give colourless needle-like crystals.Table 1 Selected bond lengths (A Ê ).

Figure 2 A
Figure 2 A packing diagram of (4), viewed down the b axis.Hydrogen bonds are indicated by dashed lines.