organic compounds
Boc-AzAla-Ala-OMe
aLaboratoire de Chimie Physique Macromoléculaire, UMR CRNS-INPL 7568, Nancy Université, BP 451, 54001 Nancy, France, and bLaboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2), Nancy Université, UMR CNRS-UHP 7036, BP 70236, 54506 Vandoeuvre-lès-Nancy, France
*Correspondence e-mail: claude.didierjean@crm2.uhp-nancy.fr
The title compound (systematic name: tert-butyl 3-{[1-(methoxycarbonyl)ethyl]aminocarbonyl}-3-methylcarbazate), C11H21N3O5, is a precursor for the study of a new class of foldamer based on aza/α-dipeptide [Abbas et al. (2009). Tetrahedron Lett. 50, 4158–4160]. The consists of one molecule in an extended conformation which is stabilized by intermolecular N—H⋯O and C—H⋯O hydrogen bonding.
Related literature
For the synthesis, see: Majer & Randad (1994); Brosse et al. (2001); Bouillon et al. (2004); Abbas et al. (2009). For the geometry of the aza-residue in azapeptides, see: Benatalah et al. (1991), André et al. (1996). For Boc-AzAla-Pro-NHiPr, see: André et al. (1997). For the procedure, see: Flack & Schwarzenbach (1988). For hydrogen-bond motifs, see: Etter (1990).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: COLLECT (Bruker, 2004); cell SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999).
Supporting information
10.1107/S1600536809045498/dn2501sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536809045498/dn2501Isup2.hkl
The title compound was prepared from N-tert-butyloxycarbonylaminophtalimide (Abbas et al., 2009), and was crystallized by slow evaporation of a diethyl ether solution.
Because of the lack of any significant
effects, the absolute configurations of the title compound could not be determined from the diffraction experiments but was known from the method of synthesis. The origin was fixed by floating-origin restraints (Flack & Schwarzenbach, 1988). All H atoms were located in difference Fourier maps. The C/N-bonded H atoms were placed at calculated positions and refined using a riding model, with C—H distances of 0.96–0.98 Å and with N—H distance of 0.86 Å. The H-atom Uiso parameters were fixed at 1.2Ueq(C) for methine C—H, at 1.2Ueq(N) for the N—H group and at 1.5Ueq(C) for methyl C—H.Data collection: COLLECT (Bruker, 2004); cell
SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999).C11H21N3O5 | Dx = 1.207 Mg m−3 |
Mr = 275.31 | Mo Kα radiation, λ = 0.71073 Å |
Tetragonal, P41 | Cell parameters from 14534 reflections |
Hall symbol: P 4w | θ = 2.5–27.9° |
a = 9.3194 (4) Å | µ = 0.10 mm−1 |
c = 17.4420 (8) Å | T = 100 K |
V = 1514.86 (12) Å3 | Prism, colorless |
Z = 4 | 0.3 × 0.2 × 0.2 mm |
F(000) = 592 |
Nonis KappaCCD diffractometer | Rint = 0.049 |
CCD rotation images, thick slices scans | θmax = 27.8°, θmin = 2.5° |
14534 measured reflections | h = −12→12 |
1847 independent reflections | k = −12→12 |
1806 reflections with I > 2σ(I) | l = −22→22 |
Refinement on F2 | 1 restraint |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.036 | w = 1/[σ2(Fo2) + (0.0164P)2 + 0.7016P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.076 | (Δ/σ)max < 0.001 |
S = 1.12 | Δρmax = 0.17 e Å−3 |
1847 reflections | Δρmin = −0.13 e Å−3 |
178 parameters |
C11H21N3O5 | Z = 4 |
Mr = 275.31 | Mo Kα radiation |
Tetragonal, P41 | µ = 0.10 mm−1 |
a = 9.3194 (4) Å | T = 100 K |
c = 17.4420 (8) Å | 0.3 × 0.2 × 0.2 mm |
V = 1514.86 (12) Å3 |
Nonis KappaCCD diffractometer | 1806 reflections with I > 2σ(I) |
14534 measured reflections | Rint = 0.049 |
1847 independent reflections |
R[F2 > 2σ(F2)] = 0.036 | 1 restraint |
wR(F2) = 0.076 | H-atom parameters constrained |
S = 1.12 | Δρmax = 0.17 e Å−3 |
1847 reflections | Δρmin = −0.13 e Å−3 |
178 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.3488 (2) | 0.0563 (2) | 0.63461 (13) | 0.0228 (4) | |
C2 | 0.2822 (3) | −0.0204 (3) | 0.56621 (14) | 0.0311 (5) | |
H2A | 0.1902 | 0.021 | 0.5551 | 0.047* | |
H2B | 0.2706 | −0.1204 | 0.578 | 0.047* | |
H2C | 0.3438 | −0.0103 | 0.5224 | 0.047* | |
C3 | 0.2529 (3) | 0.0415 (2) | 0.70463 (14) | 0.0279 (5) | |
H3A | 0.2995 | 0.0837 | 0.7482 | 0.042* | |
H3B | 0.235 | −0.0582 | 0.7145 | 0.042* | |
H3C | 0.1635 | 0.0898 | 0.6954 | 0.042* | |
C4 | 0.5016 (3) | 0.0058 (3) | 0.64752 (15) | 0.0308 (5) | |
H4A | 0.557 | 0.022 | 0.6019 | 0.046* | |
H4B | 0.5015 | −0.0948 | 0.6594 | 0.046* | |
H4C | 0.5431 | 0.0583 | 0.6894 | 0.046* | |
O1 | 0.35134 (16) | 0.20833 (15) | 0.60837 (9) | 0.0218 (3) | |
C5 | 0.3987 (2) | 0.3109 (2) | 0.65626 (12) | 0.0193 (4) | |
O2 | 0.43957 (17) | 0.29435 (17) | 0.72181 (9) | 0.0239 (3) | |
N1 | 0.39666 (19) | 0.44041 (18) | 0.61993 (11) | 0.0201 (4) | |
H1 | 0.3753 | 0.4464 | 0.5721 | 0.024* | |
N2 | 0.43006 (19) | 0.56280 (19) | 0.66214 (11) | 0.0200 (4) | |
C6 | 0.3156 (2) | 0.6117 (2) | 0.71325 (14) | 0.0259 (5) | |
H6A | 0.2304 | 0.63 | 0.6839 | 0.039* | |
H6B | 0.3451 | 0.6982 | 0.7386 | 0.039* | |
H6C | 0.2961 | 0.5389 | 0.7508 | 0.039* | |
C7 | 0.5716 (2) | 0.5760 (2) | 0.68660 (12) | 0.0189 (4) | |
O3 | 0.60321 (16) | 0.65021 (16) | 0.74280 (8) | 0.0221 (3) | |
N3 | 0.67193 (19) | 0.50835 (19) | 0.64451 (10) | 0.0209 (4) | |
H3 | 0.6487 | 0.4606 | 0.6042 | 0.025* | |
C8 | 0.8201 (2) | 0.5181 (2) | 0.66902 (13) | 0.0232 (4) | |
H8 | 0.8264 | 0.478 | 0.7209 | 0.028* | |
C9 | 0.9146 (2) | 0.4274 (3) | 0.61671 (14) | 0.0296 (5) | |
H9A | 0.8853 | 0.3288 | 0.6198 | 0.044* | |
H9B | 1.0129 | 0.4358 | 0.6326 | 0.044* | |
H9C | 0.9052 | 0.4605 | 0.5648 | 0.044* | |
C10 | 0.8773 (2) | 0.6709 (3) | 0.67187 (13) | 0.0244 (4) | |
O4 | 0.97394 (18) | 0.7060 (2) | 0.71417 (11) | 0.0333 (4) | |
O5 | 0.81613 (16) | 0.75824 (17) | 0.62089 (9) | 0.0249 (3) | |
C11 | 0.8685 (3) | 0.9048 (3) | 0.62253 (16) | 0.0310 (5) | |
H11A | 0.8424 | 0.9487 | 0.6703 | 0.046* | |
H11B | 0.8267 | 0.9578 | 0.581 | 0.046* | |
H11C | 0.971 | 0.9048 | 0.6174 | 0.046* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0313 (11) | 0.0171 (9) | 0.0199 (10) | −0.0034 (8) | 0.0039 (9) | 0.0017 (8) |
C2 | 0.0429 (14) | 0.0269 (12) | 0.0236 (11) | −0.0138 (10) | 0.0058 (10) | −0.0039 (9) |
C3 | 0.0345 (12) | 0.0232 (10) | 0.0261 (11) | −0.0033 (9) | 0.0091 (10) | −0.0012 (9) |
C4 | 0.0339 (11) | 0.0269 (11) | 0.0317 (12) | 0.0044 (9) | 0.0059 (10) | 0.0039 (10) |
O1 | 0.0288 (8) | 0.0190 (7) | 0.0178 (7) | −0.0036 (6) | −0.0026 (6) | 0.0000 (6) |
C5 | 0.0183 (9) | 0.0217 (10) | 0.0180 (10) | −0.0021 (7) | 0.0011 (8) | −0.0017 (8) |
O2 | 0.0304 (8) | 0.0240 (8) | 0.0172 (7) | −0.0031 (6) | −0.0033 (6) | 0.0007 (6) |
N1 | 0.0251 (9) | 0.0199 (8) | 0.0155 (8) | −0.0020 (7) | −0.0033 (7) | −0.0001 (7) |
N2 | 0.0217 (8) | 0.0204 (8) | 0.0178 (8) | −0.0010 (6) | 0.0005 (7) | −0.0014 (7) |
C6 | 0.0224 (10) | 0.0256 (11) | 0.0295 (12) | 0.0017 (8) | 0.0029 (9) | −0.0037 (9) |
C7 | 0.0213 (10) | 0.0190 (9) | 0.0164 (10) | −0.0028 (8) | 0.0009 (7) | 0.0023 (8) |
O3 | 0.0240 (8) | 0.0256 (8) | 0.0165 (7) | −0.0023 (6) | 0.0026 (6) | −0.0024 (6) |
N3 | 0.0197 (8) | 0.0273 (9) | 0.0157 (8) | −0.0014 (7) | 0.0003 (7) | −0.0035 (7) |
C8 | 0.0212 (10) | 0.0306 (11) | 0.0179 (10) | 0.0013 (8) | −0.0020 (8) | 0.0005 (9) |
C9 | 0.0231 (11) | 0.0413 (13) | 0.0243 (11) | 0.0049 (9) | 0.0008 (9) | −0.0043 (10) |
C10 | 0.0186 (10) | 0.0357 (12) | 0.0188 (10) | 0.0012 (9) | 0.0007 (8) | −0.0009 (9) |
O4 | 0.0263 (8) | 0.0421 (10) | 0.0316 (9) | −0.0027 (7) | −0.0105 (7) | −0.0012 (8) |
O5 | 0.0228 (8) | 0.0301 (8) | 0.0217 (8) | −0.0039 (6) | −0.0038 (6) | 0.0018 (7) |
C11 | 0.0283 (12) | 0.0330 (12) | 0.0317 (12) | −0.0052 (9) | −0.0019 (10) | 0.0031 (10) |
C1—O1 | 1.489 (2) | C6—H6A | 0.96 |
C1—C4 | 1.517 (3) | C6—H6B | 0.96 |
C1—C3 | 1.520 (3) | C6—H6C | 0.96 |
C1—C2 | 1.523 (3) | C7—O3 | 1.235 (3) |
C2—H2A | 0.96 | C7—N3 | 1.346 (3) |
C2—H2B | 0.96 | N3—C8 | 1.448 (3) |
C2—H2C | 0.96 | N3—H3 | 0.86 |
C3—H3A | 0.96 | C8—C10 | 1.521 (3) |
C3—H3B | 0.96 | C8—C9 | 1.524 (3) |
C3—H3C | 0.96 | C8—H8 | 0.98 |
C4—H4A | 0.96 | C9—H9A | 0.96 |
C4—H4B | 0.96 | C9—H9B | 0.96 |
C4—H4C | 0.96 | C9—H9C | 0.96 |
O1—C5 | 1.344 (2) | C10—O4 | 1.210 (3) |
C5—O2 | 1.215 (3) | C10—O5 | 1.334 (3) |
C5—N1 | 1.363 (3) | O5—C11 | 1.450 (3) |
N1—N2 | 1.393 (2) | C11—H11A | 0.96 |
N1—H1 | 0.86 | C11—H11B | 0.96 |
N2—C7 | 1.392 (3) | C11—H11C | 0.96 |
N2—C6 | 1.463 (3) | ||
O1—C1—C4 | 109.01 (17) | N2—C6—H6A | 109.5 |
O1—C1—C3 | 110.01 (17) | N2—C6—H6B | 109.5 |
C4—C1—C3 | 113.9 (2) | H6A—C6—H6B | 109.5 |
O1—C1—C2 | 102.26 (17) | N2—C6—H6C | 109.5 |
C4—C1—C2 | 110.7 (2) | H6A—C6—H6C | 109.5 |
C3—C1—C2 | 110.32 (19) | H6B—C6—H6C | 109.5 |
C1—C2—H2A | 109.5 | O3—C7—N3 | 122.0 (2) |
C1—C2—H2B | 109.5 | O3—C7—N2 | 121.24 (19) |
H2A—C2—H2B | 109.5 | N3—C7—N2 | 116.72 (18) |
C1—C2—H2C | 109.5 | C7—N3—C8 | 118.14 (18) |
H2A—C2—H2C | 109.5 | C7—N3—H3 | 120.9 |
H2B—C2—H2C | 109.5 | C8—N3—H3 | 120.9 |
C1—C3—H3A | 109.5 | N3—C8—C10 | 113.75 (18) |
C1—C3—H3B | 109.5 | N3—C8—C9 | 109.84 (18) |
H3A—C3—H3B | 109.5 | C10—C8—C9 | 109.64 (19) |
C1—C3—H3C | 109.5 | N3—C8—H8 | 107.8 |
H3A—C3—H3C | 109.5 | C10—C8—H8 | 107.8 |
H3B—C3—H3C | 109.5 | C9—C8—H8 | 107.8 |
C1—C4—H4A | 109.5 | C8—C9—H9A | 109.5 |
C1—C4—H4B | 109.5 | C8—C9—H9B | 109.5 |
H4A—C4—H4B | 109.5 | H9A—C9—H9B | 109.5 |
C1—C4—H4C | 109.5 | C8—C9—H9C | 109.5 |
H4A—C4—H4C | 109.5 | H9A—C9—H9C | 109.5 |
H4B—C4—H4C | 109.5 | H9B—C9—H9C | 109.5 |
C5—O1—C1 | 119.40 (17) | O4—C10—O5 | 124.0 (2) |
O2—C5—O1 | 126.7 (2) | O4—C10—C8 | 122.3 (2) |
O2—C5—N1 | 123.66 (19) | O5—C10—C8 | 113.58 (18) |
O1—C5—N1 | 109.64 (18) | C10—O5—C11 | 114.71 (18) |
C5—N1—N2 | 118.43 (18) | O5—C11—H11A | 109.5 |
C5—N1—H1 | 120.8 | O5—C11—H11B | 109.5 |
N2—N1—H1 | 120.8 | H11A—C11—H11B | 109.5 |
C7—N2—N1 | 116.51 (17) | O5—C11—H11C | 109.5 |
C7—N2—C6 | 118.49 (18) | H11A—C11—H11C | 109.5 |
N1—N2—C6 | 114.46 (17) | H11B—C11—H11C | 109.5 |
C4—C1—O1—C5 | −65.6 (2) | C6—N2—C7—N3 | 168.95 (18) |
C3—C1—O1—C5 | 60.0 (2) | O3—C7—N3—C8 | 3.2 (3) |
C2—C1—O1—C5 | 177.16 (18) | N2—C7—N3—C8 | −179.09 (18) |
C1—O1—C5—O2 | −1.3 (3) | C7—N3—C8—C10 | −60.0 (3) |
C1—O1—C5—N1 | 177.86 (17) | C7—N3—C8—C9 | 176.65 (19) |
O2—C5—N1—N2 | −6.4 (3) | N3—C8—C10—O4 | 153.4 (2) |
O1—C5—N1—N2 | 174.45 (17) | C9—C8—C10—O4 | −83.2 (3) |
C5—N1—N2—C7 | 68.4 (2) | N3—C8—C10—O5 | −30.0 (3) |
C5—N1—N2—C6 | −75.9 (2) | C9—C8—C10—O5 | 93.5 (2) |
N1—N2—C7—O3 | −156.14 (19) | O4—C10—O5—C11 | −3.6 (3) |
C6—N2—C7—O3 | −13.3 (3) | C8—C10—O5—C11 | 179.84 (19) |
N1—N2—C7—N3 | 26.1 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2i | 0.86 | 2.18 | 2.972 (2) | 153 |
N3—H3···O3i | 0.86 | 2.03 | 2.850 (2) | 159 |
C6—H6A···O4ii | 0.96 | 2.55 | 3.303 (3) | 136 |
C11—H11B···O4iii | 0.96 | 2.41 | 3.346 (3) | 164 |
Symmetry codes: (i) y, −x+1, z−1/4; (ii) x−1, y, z; (iii) y, −x+2, z−1/4. |
Experimental details
Crystal data | |
Chemical formula | C11H21N3O5 |
Mr | 275.31 |
Crystal system, space group | Tetragonal, P41 |
Temperature (K) | 100 |
a, c (Å) | 9.3194 (4), 17.4420 (8) |
V (Å3) | 1514.86 (12) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.3 × 0.2 × 0.2 |
Data collection | |
Diffractometer | Nonis KappaCCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 14534, 1847, 1806 |
Rint | 0.049 |
(sin θ/λ)max (Å−1) | 0.656 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.036, 0.076, 1.12 |
No. of reflections | 1847 |
No. of parameters | 178 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.17, −0.13 |
Computer programs: COLLECT (Bruker, 2004), DENZO and SCALEPACK (Otwinowski & Minor, 1997), SIR92 (Altomare et al., 1994), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2009), WinGX (Farrugia, 1999).
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2i | 0.86 | 2.18 | 2.972 (2) | 152.9 |
N3—H3···O3i | 0.86 | 2.03 | 2.850 (2) | 158.7 |
C6—H6A···O4ii | 0.96 | 2.55 | 3.303 (3) | 135.6 |
C11—H11B···O4iii | 0.96 | 2.41 | 3.346 (3) | 164.3 |
Symmetry codes: (i) y, −x+1, z−1/4; (ii) x−1, y, z; (iii) y, −x+2, z−1/4. |
Acknowledgements
The authors thank the National Research Agency (ANR) for financial support (No. NT05_4_42848). Support from Nancy Université for the X-ray measurements is gratefully acknowledged
References
Abbas, C., Pickaert, G., Didierjean, C., Grégoire, B. J. & Vanderesse, R. (2009). Tetrahedron Lett. 50, 4158–4160. Web of Science CSD CrossRef CAS Google Scholar
Altomare, A., Cascarano, G., Giacovazzo, C., Guagliardi, A., Burla, M. C., Polidori, G. & Camalli, M. (1994). J. Appl. Cryst. 27, 435. CrossRef Web of Science IUCr Journals Google Scholar
André, F., Boussard, G., Bayeul, D., Didierjean, C., Aubry, A. & Marraud, M. (1997). J. Pept. Res. 49, 556–562. PubMed Web of Science Google Scholar
André, F., Marraud, M., Boussard, G., Didierjean, C. & Aubry, A. (1996). Tetrahedron Lett. 37, 183–186. Google Scholar
Benatalah, Z., Aubry, A., Boussard, G. & Marraud, M. (1991). Int. J. Pept. Protein Res. 38, 603–605. CrossRef PubMed CAS Web of Science Google Scholar
Bouillon, I., Brosse, N., Vanderesse, R. & Jamart-Grégoire, B. (2004). Tetrahedron Lett. 45, 3569–3572. Web of Science CrossRef CAS Google Scholar
Brosse, N., Pinto, M.-F., Bodiguel, J. & Jamart-Gregoire, B. (2001). J. Org. Chem. 66, 2869–2873. Web of Science CrossRef PubMed CAS Google Scholar
Bruker (2004). COLLECT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126. CrossRef CAS Web of Science Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Flack, H. D. & Schwarzenbach, D. (1988). Acta Cryst. A44, 499–506. CrossRef CAS Web of Science IUCr Journals Google Scholar
Majer, P. & Randad, R. S. (1994). J. Org. Chem. 59, 1937–1938. CrossRef CAS Web of Science Google Scholar
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
As part of our continuing studies on the synthesis and structure of hydrazino-and N-amino-peptides, we recently described the original and efficient synthesis of aza/α-dipeptides via Mitsunobu and trans-protections protocols starting from N-tert-butyloxycarbonylaminophtalimide (Abbas et al., 2009; Majer & Randad 1994; Brosse et al. 2001; Bouillon et al. 2004). Aza-peptides are pseudopeptides, in which nitrogen has been substituted for at least one of the CHα groups. Here we report the crystal structure of the pseudodipeptide Boc-AzAla-Ala-OMe (Fig. 1).
In the present study, the geometry of the aza-residue is similar to those observed for known azapeptides structures. In most of the cases, the α-nitrogen adopts a non-planar planar structure (André et al., 1996; Benatalah et al. 1991). In the title compound, the deviation of the α-nitrogen out of the plane, defined by the three atoms bonded to it, is 0.268 (2) Å. The greatest difference from standard peptide group concern the bond lengths and bond angles around the α-nitrogen: (i) the N—Nα (N1—N2) and Nα—Cβ (N2—C6) bonds are shorter by about 0.06Å than their homologous bonds in peptides; (ii) the Nα—C' ((N2—C7) bond of 1.392 (3)Å is shorter than the homologous Cα—C' bond and exceeds the dimension of the amide bond; (iii) the bond angles around the α-nitrogen are larger by 5–6° than the bond angles around the α-carbon.
In the solid state, Boc-AzAla-Pro-NHiPr (André et al., 1997) and the title compound Boc-AzAla-Ala-OMe adopt two distinct conformations with the Nα atoms having opposite configurations. In the former, the AzAla residue assumes the R chirality and the pseudodipeptide is folded by an intramolecular hydrogen bond between the (iPr)NH and the Boc(CO) groups. In the crystal of the title compound, the pseudodipeptides adopt an extended conformation which form infinite chains along the four fold axis. The N-H goups of AzaAla and Ala residues are engaged in intermolecular hydrogen bonds with the carbonyl groups of the N-terminal protecting group and the aza-residue, respectively, forming two C(4) chain motifs (Fig. 2, Etter 1990). Combination of these two motifs generates a new R22(12) pattern, shown in the Fig. 2. Finally, the third carbonyl group, C10=O4, is involved in weak CH···O hydrogen bonds forming a threedimensional network structure.