organic compounds
(3R,4R,5R)-5-(Acetamidomethyl)-N-benzyl-3,4-dihydroxytetrahydrofuran-3-carboxamide
aChemistry Research Laboratory, University of, Oxford, Mansfield Road, Oxford, OX1 3TA, England
*Correspondence e-mail: michela.simone@chem.ox.ac.uk
X-ray crystallographic analysis with Cu Kα radiation established the relative configurations of the stereogenic centers in the title compound, C15H20N2O5, and clarified mechanistic ambiguities in the synthesis. The conformation of the five-membered ring approximates twisted, about a C—O bond. The of this carbon-branched dipeptide isostere was known based on the use of D-ribose as the starting material. of the gave an ambiguous result but the refined Hooft parameter is in agreement with the assumed (D-ribose) The consists of N—H⋯O and O—H⋯O hydrogen-bonded bi-layers, with the terminal methyl and phenyl groups forming a hydrophobic inter-layer interface. Some weak C—H⋯O interactions are also present.
Related literature
For reviews of sugar amino acids, see: Risseeuw et al. (2007); Smith & Fleet (1999). For investigations of peptidomimetics, see: Smith et al. (1998); Long et al. (1998, 1999); Claridge et al. (1999); Brittain et al. (2000); Hungerford et al. (2000); Raunkjr et al. (2004); Jockusch et al. (2006); Tuin et al. (2009). For crossed-aldol reactions of with formaldehyde, see: Ho (1985); Simone et al. (2005, 2008); Best et al. (2010). For more strategies for the synthesis of branched see: Hotchkiss et al. (2004); Soengas et al. (2005); Booth et al. (2008). For a related structure, see: Punzo et al. (2005). For the treatment of hydrogen atoms in CRYSTALS, see: Cooper et al. (2010). For the determination of see: Hooft et al. (2008).
Experimental
Crystal data
|
Data collection: Gemini (Oxford Diffraction, 2006); cell CrysAlis RED (Oxford Diffraction, 2002); data reduction: CrysAlis RED; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS.
Supporting information
https://doi.org/10.1107/S1600536810039589/hb5639sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810039589/hb5639Isup2.hkl
Compound (4) was dissolved in methanol, ethyl acetate and cyclohexane and then crystallized as the solvent (methanol) evaporated slowly to give crystals of (I) as very thin fragile colourless plates, which readily delaminated on handling. M.p. 428.2–429.2 K; [α]D23 +0.64 (c, 0.70 in methanol) (Simone et al., 2005).
Refinement of the Flack (1983) parameter was inconclusive, 0.0 (3), but the Hooft parameter, 0.01 (6) was in agreement with the known
(Hooft et al., 2008).The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically. The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C—H in the range 0.93–0.98, N—H = 0.86, O—H = 0.82 Å) and Uiso(H) (in the range 1.2–1.5 times Ueq of the parent atom), after which the positions were refined with riding constraints (Cooper et al., 2010).
δ-Tetrahydrofuran sugar amino acids (THF SAAs) (Risseeuw et al., 2007; Smith and Fleet, 1999) have been extensively used as dipeptide isosteres (Long et al., 1998; Brittain et al., 2000) and incorporated into peptidomimetics (Smith et al., 1998; Hungerford et al., 2000; Raunkjr et al., 2004). The secondary structural preferences induced by THF SAAs upon their incorporation into peptidomimetics have been investigated in a wide variety of systems (Long et al., 1999; Tuin et al., 2009). All these studies have been reported on linear carbon chains, however a number of approaches to branched have been developed (Soengas et al., 2005; Hotchkiss et al., 2004; Booth et al., 2008). This will allow the synthesis of THF SAAs with a branched carbon chain and allow a new family of foldamers to be created.
Compound (4) is a dipeptide isostere bearing a branching carbon substituent at position C-3 of the THF scaffold. The branched peptidomimetic (4) was synthesized in a number of steps from the suitably protected D-ribose derivative (1). A crossed aldol reaction of (1) with formaldehyde (Ho, 1985) gave the resulting lactol which was then further modified to give the carbon-branched lactone trifluoromethanesulfonate (2). Reaction of (2) in acidic methanol (Simone et al., 2008) afforded the branched δ-THF SAA (3). The dipeptide isostere (4) was synthesized from SAA scaffold (3) in four synthetic steps. The of an isomeric branched peptidomimetic has been published previously (Punzo et al., 2005). The of (4) removes mechanistic ambiguities arising from the Ho crossed aldol condensation and successive modifications of the THF scaffold. Furthermore the may provide information about the conformational preference of the scaffold (4) and its corresponding ability to induce any secondary structural features when incorporated into peptidomimetics. The use of D-ribose as the starting material enabled the determination of the of this carbon-branched dipeptide isostere (4).
For reviews of sugar amino acids, see: Risseeuw et al. (2007); Smith & Fleet (1999). For investigations of peptidomimetics, see: Smith et al. (1998); Long et al. (1998, 1999); Claridge et al. (1999); Brittain et al. (2000); Hungerford et al. (2000); Raunkjr et al. (2004); Jockusch et al. (2006); Tuin et al. (2009). For crossed-aldol reactions of
with formaldehyde, see: Ho (1985); Simone et al. (2005, 2008); Best et al. (2010). For more strategies for the synthesis of branched see: Hotchkiss et al. (2004); Soengas et al. (2005); Booth et al. (2008). For a related structure, see: Punzo et al. (2005). For the treatment of hydrogen atoms in CRYSTALS, see: Cooper et al. (2010). For the determination of see: Hooft et al. (2008).Data collection: Gemini (Oxford Diffraction, 2006); cell
CrysAlis RED (Oxford Diffraction, 2002); data reduction: CrysAlis RED (Oxford Diffraction, 2002); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).Fig. 1. The title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as spheres of arbitary radius. | |
Fig. 2. The hydrogen bonded bi-layer viewed along the 'a' axis. The hydrophobic faces to the layers explains why the thin platey crystals were extremely fragile. | |
Fig. 3. Preparation of the title compound. |
C15H20N2O5 | Dx = 1.362 Mg m−3 |
Mr = 308.33 | Cu Kα radiation, λ = 1.54180 Å |
Orthorhombic, P212121 | Cell parameters from 6490 reflections |
a = 5.4130 (2) Å | θ = 2–50° |
b = 8.5082 (2) Å | µ = 0.86 mm−1 |
c = 32.6501 (4) Å | T = 150 K |
V = 1503.70 (7) Å3 | Plate, colourless |
Z = 4 | 0.35 × 0.20 × 0.04 mm |
F(000) = 656 |
Oxford Diffraction Gemini diffractometer | 1371 reflections with I > 2.0σ(I) |
Graphite monochromator | Rint = 0.038 |
ω scans | θmax = 54.3°, θmin = 5.4° |
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2002) | h = −5→5 |
Tmin = 0.95, Tmax = 0.97 | k = −8→8 |
12797 measured reflections | l = −33→34 |
1805 independent reflections |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.033 | Method = Modified Sheldrick w = 1/[σ2(F2) + ( 0.1P)2 + 0.0P] , where P = (max(Fo2,0) + 2Fc2)/3 |
wR(F2) = 0.061 | (Δ/σ)max = 0.0002818 |
S = 0.99 | Δρmax = 0.21 e Å−3 |
1796 reflections | Δρmin = −0.28 e Å−3 |
200 parameters | Absolute structure: Flack (1983), 681 Friedel pairs |
0 restraints | Absolute structure parameter: 0.0 (3) |
Primary atom site location: structure-invariant direct methods |
C15H20N2O5 | V = 1503.70 (7) Å3 |
Mr = 308.33 | Z = 4 |
Orthorhombic, P212121 | Cu Kα radiation |
a = 5.4130 (2) Å | µ = 0.86 mm−1 |
b = 8.5082 (2) Å | T = 150 K |
c = 32.6501 (4) Å | 0.35 × 0.20 × 0.04 mm |
Oxford Diffraction Gemini diffractometer | 1805 independent reflections |
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2002) | 1371 reflections with I > 2.0σ(I) |
Tmin = 0.95, Tmax = 0.97 | Rint = 0.038 |
12797 measured reflections | θmax = 54.3° |
R[F2 > 2σ(F2)] = 0.033 | H-atom parameters constrained |
wR(F2) = 0.061 | Δρmax = 0.21 e Å−3 |
S = 0.99 | Δρmin = −0.28 e Å−3 |
1796 reflections | Absolute structure: Flack (1983), 681 Friedel pairs |
200 parameters | Absolute structure parameter: 0.0 (3) |
0 restraints |
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems open-flow nitrogen cryostat (Cosier & Glazer, 1986) with a nominal stability of 0.1 K. Cosier, J. & Glazer, A.M., 1986. J. Appl. Cryst. 105 107. The 9 missing reflections are all low-angle and in the penumbra of the beam trap. Their indices are 1 0 1 0 1 1 0 1 2 0 1 3 0 0 4 0 1 4 0 1 5 0 0 6 |
x | y | z | Uiso*/Ueq | ||
O1 | 0.5384 (3) | 0.54901 (19) | 0.24407 (4) | 0.0310 | |
C2 | 0.5370 (4) | 0.5114 (3) | 0.28721 (7) | 0.0285 | |
C3 | 0.2641 (4) | 0.5070 (3) | 0.29786 (7) | 0.0260 | |
C4 | 0.1541 (4) | 0.4286 (3) | 0.25891 (7) | 0.0254 | |
C5 | 0.3580 (4) | 0.4433 (3) | 0.22659 (7) | 0.0292 | |
O6 | 0.1751 (3) | 0.6640 (2) | 0.30274 (4) | 0.0326 | |
O7 | 0.0770 (3) | 0.27045 (18) | 0.26442 (4) | 0.0315 | |
C8 | 0.2035 (5) | 0.4123 (4) | 0.33591 (8) | 0.0282 | |
O9 | 0.3097 (3) | 0.2865 (2) | 0.34244 (5) | 0.0385 | |
N10 | 0.0228 (4) | 0.4687 (2) | 0.35927 (6) | 0.0333 | |
C11 | −0.0761 (5) | 0.3862 (3) | 0.39501 (7) | 0.0386 | |
C12 | 0.0572 (5) | 0.4266 (4) | 0.43394 (8) | 0.0357 | |
C13 | 0.2683 (6) | 0.3472 (4) | 0.44544 (9) | 0.0475 | |
C14 | 0.3884 (6) | 0.3856 (4) | 0.48131 (11) | 0.0609 | |
C15 | 0.3030 (7) | 0.5041 (5) | 0.50564 (9) | 0.0650 | |
C16 | 0.0949 (7) | 0.5856 (4) | 0.49430 (9) | 0.0609 | |
C17 | −0.0278 (5) | 0.5475 (4) | 0.45838 (8) | 0.0465 | |
C18 | 0.2707 (4) | 0.5031 (3) | 0.18519 (7) | 0.0335 | |
N19 | 0.4531 (4) | 0.4865 (2) | 0.15327 (6) | 0.0334 | |
C20 | 0.4739 (5) | 0.3543 (4) | 0.13069 (8) | 0.0327 | |
O21 | 0.3280 (4) | 0.2440 (2) | 0.13419 (5) | 0.0418 | |
C22 | 0.6860 (5) | 0.3518 (3) | 0.10127 (8) | 0.0482 | |
H61 | 0.1223 | 0.6945 | 0.2814 | 0.0479* | |
H71 | 0.1969 | 0.2186 | 0.2694 | 0.0465* | |
H101 | −0.0317 | 0.5582 | 0.3538 | 0.0384* | |
H191 | 0.5586 | 0.5638 | 0.1497 | 0.0387* | |
H22 | 0.6302 | 0.5904 | 0.3029 | 0.0333* | |
H21 | 0.6124 | 0.4078 | 0.2913 | 0.0332* | |
H41 | 0.0066 | 0.4876 | 0.2499 | 0.0266* | |
H51 | 0.4304 | 0.3372 | 0.2225 | 0.0326* | |
H111 | −0.2474 | 0.4142 | 0.3983 | 0.0447* | |
H112 | −0.0631 | 0.2706 | 0.3888 | 0.0441* | |
H131 | 0.3326 | 0.2659 | 0.4287 | 0.0566* | |
H141 | 0.5300 | 0.3272 | 0.4883 | 0.0728* | |
H151 | 0.3864 | 0.5282 | 0.5307 | 0.0784* | |
H161 | 0.0278 | 0.6652 | 0.5111 | 0.0716* | |
H171 | −0.1695 | 0.6031 | 0.4505 | 0.0557* | |
H181 | 0.2260 | 0.6167 | 0.1869 | 0.0395* | |
H182 | 0.1239 | 0.4446 | 0.1778 | 0.0396* | |
H223 | 0.6719 | 0.2678 | 0.0820 | 0.0701* | |
H222 | 0.8402 | 0.3475 | 0.1150 | 0.0711* | |
H221 | 0.6889 | 0.4446 | 0.0854 | 0.0713* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0310 (9) | 0.0329 (11) | 0.0290 (10) | −0.0035 (9) | −0.0004 (8) | 0.0013 (9) |
C2 | 0.0288 (17) | 0.0261 (19) | 0.0305 (16) | 0.0022 (15) | −0.0051 (13) | 0.0002 (13) |
C3 | 0.0303 (17) | 0.0240 (19) | 0.0237 (16) | 0.0006 (15) | 0.0003 (12) | 0.0029 (14) |
C4 | 0.0291 (14) | 0.0156 (18) | 0.0313 (16) | 0.0013 (13) | −0.0048 (14) | 0.0002 (14) |
C5 | 0.0299 (15) | 0.0260 (18) | 0.0316 (16) | −0.0019 (16) | 0.0001 (13) | −0.0043 (15) |
O6 | 0.0433 (11) | 0.0236 (13) | 0.0309 (11) | 0.0047 (10) | −0.0042 (9) | −0.0010 (9) |
O7 | 0.0303 (11) | 0.0251 (12) | 0.0390 (10) | −0.0027 (9) | −0.0010 (8) | −0.0005 (9) |
C8 | 0.0280 (17) | 0.028 (2) | 0.0287 (18) | −0.0011 (17) | −0.0022 (15) | −0.0061 (16) |
O9 | 0.0453 (12) | 0.0285 (12) | 0.0417 (12) | 0.0080 (11) | 0.0038 (10) | 0.0052 (10) |
N10 | 0.0378 (13) | 0.0288 (15) | 0.0334 (13) | 0.0078 (13) | −0.0003 (12) | 0.0038 (11) |
C11 | 0.0394 (18) | 0.044 (2) | 0.0322 (17) | −0.0018 (16) | 0.0059 (15) | 0.0031 (15) |
C12 | 0.0366 (18) | 0.042 (2) | 0.0282 (17) | −0.0039 (18) | 0.0041 (16) | 0.0094 (17) |
C13 | 0.048 (2) | 0.054 (2) | 0.041 (2) | −0.003 (2) | 0.0050 (18) | 0.0083 (18) |
C14 | 0.046 (2) | 0.077 (3) | 0.059 (2) | −0.009 (2) | −0.008 (2) | 0.021 (2) |
C15 | 0.072 (3) | 0.081 (3) | 0.042 (2) | −0.022 (3) | −0.010 (2) | 0.005 (2) |
C16 | 0.072 (3) | 0.066 (3) | 0.044 (2) | −0.007 (2) | 0.007 (2) | −0.0091 (19) |
C17 | 0.0511 (19) | 0.050 (2) | 0.0382 (18) | 0.0005 (19) | 0.0049 (18) | 0.0023 (17) |
C18 | 0.0340 (16) | 0.032 (2) | 0.0346 (17) | −0.0018 (15) | 0.0013 (14) | −0.0018 (15) |
N19 | 0.0367 (13) | 0.0319 (16) | 0.0318 (13) | −0.0115 (13) | 0.0074 (12) | −0.0025 (12) |
C20 | 0.0385 (19) | 0.034 (2) | 0.0254 (16) | 0.0013 (19) | −0.0072 (17) | 0.0015 (17) |
O21 | 0.0472 (13) | 0.0319 (14) | 0.0462 (12) | −0.0103 (11) | 0.0017 (11) | −0.0039 (10) |
C22 | 0.052 (2) | 0.054 (2) | 0.0389 (18) | 0.0002 (18) | 0.0118 (17) | −0.0006 (16) |
O1—C2 | 1.444 (2) | C12—C13 | 1.379 (3) |
O1—C5 | 1.445 (3) | C12—C17 | 1.381 (4) |
C2—C3 | 1.518 (3) | C13—C14 | 1.379 (4) |
C2—H22 | 0.983 | C13—H131 | 0.948 |
C2—H21 | 0.981 | C14—C15 | 1.364 (4) |
C3—C4 | 1.555 (3) | C14—H141 | 0.941 |
C3—O6 | 1.429 (3) | C15—C16 | 1.373 (4) |
C3—C8 | 1.517 (3) | C15—H151 | 0.956 |
C4—C5 | 1.532 (3) | C16—C17 | 1.386 (3) |
C4—O7 | 1.420 (2) | C16—H161 | 0.945 |
C4—H41 | 0.988 | C17—H171 | 0.937 |
C5—C18 | 1.520 (3) | C18—N19 | 1.443 (3) |
C5—H51 | 0.993 | C18—H181 | 0.998 |
O6—H61 | 0.796 | C18—H182 | 0.968 |
O7—H71 | 0.801 | N19—C20 | 1.350 (3) |
C8—O9 | 1.234 (3) | N19—H191 | 0.879 |
C8—N10 | 1.330 (3) | C20—O21 | 1.232 (3) |
N10—C11 | 1.463 (3) | C20—C22 | 1.497 (3) |
N10—H101 | 0.836 | C22—H223 | 0.956 |
C11—C12 | 1.501 (3) | C22—H222 | 0.947 |
C11—H111 | 0.963 | C22—H221 | 0.945 |
C11—H112 | 1.007 | ||
C2—O1—C5 | 104.10 (17) | H111—C11—H112 | 109.4 |
O1—C2—C3 | 103.53 (17) | C11—C12—C13 | 121.1 (3) |
O1—C2—H22 | 110.7 | C11—C12—C17 | 120.0 (3) |
C3—C2—H22 | 113.4 | C13—C12—C17 | 118.9 (3) |
O1—C2—H21 | 109.3 | C12—C13—C14 | 120.4 (3) |
C3—C2—H21 | 110.6 | C12—C13—H131 | 120.3 |
H22—C2—H21 | 109.2 | C14—C13—H131 | 119.3 |
C2—C3—C4 | 101.29 (19) | C13—C14—C15 | 120.7 (3) |
C2—C3—O6 | 109.3 (2) | C13—C14—H141 | 117.6 |
C4—C3—O6 | 111.3 (2) | C15—C14—H141 | 121.7 |
C2—C3—C8 | 114.3 (2) | C14—C15—C16 | 119.6 (3) |
C4—C3—C8 | 111.0 (2) | C14—C15—H151 | 119.8 |
O6—C3—C8 | 109.4 (2) | C16—C15—H151 | 120.6 |
C3—C4—C5 | 104.63 (19) | C15—C16—C17 | 120.2 (3) |
C3—C4—O7 | 114.56 (19) | C15—C16—H161 | 121.4 |
C5—C4—O7 | 112.09 (19) | C17—C16—H161 | 118.3 |
C3—C4—H41 | 109.5 | C16—C17—C12 | 120.2 (3) |
C5—C4—H41 | 109.7 | C16—C17—H171 | 120.5 |
O7—C4—H41 | 106.4 | C12—C17—H171 | 119.3 |
C4—C5—O1 | 105.40 (17) | C5—C18—N19 | 113.39 (19) |
C4—C5—C18 | 114.6 (2) | C5—C18—H181 | 110.5 |
O1—C5—C18 | 110.66 (19) | N19—C18—H181 | 107.5 |
C4—C5—H51 | 107.7 | C5—C18—H182 | 107.8 |
O1—C5—H51 | 110.6 | N19—C18—H182 | 109.3 |
C18—C5—H51 | 107.9 | H181—C18—H182 | 108.2 |
C3—O6—H61 | 109.1 | C18—N19—C20 | 122.2 (2) |
C4—O7—H71 | 108.0 | C18—N19—H191 | 117.8 |
C3—C8—O9 | 120.1 (2) | C20—N19—H191 | 119.9 |
C3—C8—N10 | 115.9 (3) | N19—C20—O21 | 122.1 (2) |
O9—C8—N10 | 123.8 (2) | N19—C20—C22 | 115.2 (3) |
C8—N10—C11 | 123.6 (2) | O21—C20—C22 | 122.7 (3) |
C8—N10—H101 | 117.8 | C20—C22—H223 | 111.9 |
C11—N10—H101 | 118.5 | C20—C22—H222 | 111.9 |
N10—C11—C12 | 112.9 (2) | H223—C22—H222 | 110.6 |
N10—C11—H111 | 108.9 | C20—C22—H221 | 110.7 |
C12—C11—H111 | 108.1 | H223—C22—H221 | 105.3 |
N10—C11—H112 | 106.4 | H222—C22—H221 | 106.0 |
C12—C11—H112 | 111.2 |
D—H···A | D—H | H···A | D···A | D—H···A |
O6—H61···O7i | 0.80 | 1.95 | 2.737 (4) | 167 |
O7—H71···O1ii | 0.80 | 2.08 | 2.821 (4) | 154 |
N10—H101···O21i | 0.84 | 2.29 | 3.023 (4) | 147 |
N19—H191···O9iii | 0.88 | 2.04 | 2.861 (4) | 155 |
C2—H22···O21iii | 0.98 | 2.45 | 3.322 (4) | 148 |
C4—H41···O1iv | 0.99 | 2.59 | 3.520 (4) | 156 |
C4—H41···O7i | 0.99 | 2.49 | 3.257 (4) | 134 |
Symmetry codes: (i) −x, y+1/2, −z+1/2; (ii) −x+1, y−1/2, −z+1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) x−1, y, z. |
Experimental details
Crystal data | |
Chemical formula | C15H20N2O5 |
Mr | 308.33 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 150 |
a, b, c (Å) | 5.4130 (2), 8.5082 (2), 32.6501 (4) |
V (Å3) | 1503.70 (7) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 0.86 |
Crystal size (mm) | 0.35 × 0.20 × 0.04 |
Data collection | |
Diffractometer | Oxford Diffraction Gemini |
Absorption correction | Multi-scan (CrysAlis RED; Oxford Diffraction, 2002) |
Tmin, Tmax | 0.95, 0.97 |
No. of measured, independent and observed [I > 2.0σ(I)] reflections | 12797, 1805, 1371 |
Rint | 0.038 |
θmax (°) | 54.3 |
(sin θ/λ)max (Å−1) | 0.527 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.061, 0.99 |
No. of reflections | 1796 |
No. of parameters | 200 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.21, −0.28 |
Absolute structure | Flack (1983), 681 Friedel pairs |
Absolute structure parameter | 0.0 (3) |
Computer programs: Gemini (Oxford Diffraction, 2006), CrysAlis RED (Oxford Diffraction, 2002), SIR92 (Altomare et al., 1994), CRYSTALS (Betteridge et al., 2003), CAMERON (Watkin et al., 1996).
D—H···A | D—H | H···A | D···A | D—H···A |
O6—H61···O7i | 0.80 | 1.95 | 2.737 (4) | 167 |
O7—H71···O1ii | 0.80 | 2.08 | 2.821 (4) | 154 |
N10—H101···O21i | 0.84 | 2.29 | 3.023 (4) | 147 |
N19—H191···O9iii | 0.88 | 2.04 | 2.861 (4) | 155 |
C2—H22···O21iii | 0.98 | 2.45 | 3.322 (4) | 148 |
C4—H41···O1iv | 0.99 | 2.59 | 3.520 (4) | 156 |
C4—H41···O7i | 0.99 | 2.49 | 3.257 (4) | 134 |
Symmetry codes: (i) −x, y+1/2, −z+1/2; (ii) −x+1, y−1/2, −z+1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) x−1, y, z. |
Footnotes
‡Present address: Medway School of Pharmacy, Universities of Kent and Greenwich at Medway, Central Avenue, Chatham Maritime, Kent, ME4 4TB, England.
Acknowledgements
Financial support to MIS provided through the European Community's Human Potential Programme under contract HPRN-CT-2002–00173 is gratefully acknowledged.
References
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δ-Tetrahydrofuran sugar amino acids (THF SAAs) (Risseeuw et al., 2007; Smith and Fleet, 1999) have been extensively used as dipeptide isosteres (Long et al., 1998; Brittain et al., 2000) and incorporated into peptidomimetics (Smith et al., 1998; Hungerford et al., 2000; Raunkjr et al., 2004). The secondary structural preferences induced by THF SAAs upon their incorporation into peptidomimetics have been investigated in a wide variety of systems (Long et al., 1999; Tuin et al., 2009). All these studies have been reported on linear carbon chains, however a number of approaches to branched carbohydrates have been developed (Soengas et al., 2005; Hotchkiss et al., 2004; Booth et al., 2008). This will allow the synthesis of THF SAAs with a branched carbon chain and allow a new family of foldamers to be created.
Compound (4) is a dipeptide isostere bearing a branching carbon substituent at position C-3 of the THF scaffold. The branched peptidomimetic (4) was synthesized in a number of steps from the suitably protected D-ribose derivative (1). A crossed aldol reaction of (1) with formaldehyde (Ho, 1985) gave the resulting lactol which was then further modified to give the carbon-branched lactone trifluoromethanesulfonate (2). Reaction of (2) in acidic methanol (Simone et al., 2008) afforded the branched δ-THF SAA (3). The dipeptide isostere (4) was synthesized from SAA scaffold (3) in four synthetic steps. The crystal structure of an isomeric branched peptidomimetic has been published previously (Punzo et al., 2005). The crystal structure of (4) removes mechanistic ambiguities arising from the Ho crossed aldol condensation and successive modifications of the THF scaffold. Furthermore the crystal structure may provide information about the conformational preference of the scaffold (4) and its corresponding ability to induce any secondary structural features when incorporated into peptidomimetics. The use of D-ribose as the starting material enabled the determination of the absolute configuration of this carbon-branched dipeptide isostere (4).