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The title dipeptide {systematic name: (S)-2-[(S)-2-azaniumyl­butan­amido]-3-hy­droxy­propanoate}, C7H14N2O4, was syn­thesized in the anticipation that it would form nano­porous crystals with hexa­gonal symmetry. Single-crystal X-ray diffraction analysis showed that it had instead adopted a unit cell in the space group I4, similar to L-alanyl-L-alanine [Fletterick, Tsai & Hughes (1970). J. Phys. Chem. 75, 918-922]. The resulting packing arrangement has a high density for a peptide (1.462 Mg m-3), which is rendered possible by extensive disorder over two positions for the ethyl side chain of the 2-amino­butyric acid fragment and over three positions for the serine side chain.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270113017484/qs3026sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270113017484/qs3026Isup2.hkl
Contains datablock I

cml

Chemical Markup Language (CML) file https://doi.org/10.1107/S0108270113017484/qs3026Isup3.cml
Supplementary material

CCDC reference: 963383

Introduction top

Dipeptides form nanoporous structures belonging to three different classes (Görbitz, 2007): the Val–Ala class with hydro­phobic pores (all amino acids discussed in this paper are of the L configuration, stereochemical indicators are thus not included), the Phe–Phe class with hydro­philic pores, and, with just a single member, the Leu–Ser class with hydro­phobic pores [Görbitz et al., 2005; Cambridge Structural Database (CSD; Allen, 2002) refcode JAZBOC]. Val–Ser (Görbitz, 2005a; Johansen et al., 2005) and Ile–Ser (Görbitz et al., 2006) were subsequently investigated in the search for additional Leu–Ser class structures, but yielded other types of structure. A careful analysis of the Leu–Ser crystal packing then revealed that it is in fact incompatible with side-chain branching at Cβ, as this would inevitably lead to steric conflict with main-chain atoms. Met–Ser (Görbitz et al., 2006) furthermore produced a layered packing arrangement (obtained as a 0.34-hydrate). Consequently, additional members of the Leu–Ser family, preferentially with even wider channels, had to be sought among dipeptides with other hydro­phobic and unbranched side chains at the N-terminal end. We have now synthesized two new dipeptides with nonproteinogenic amino acid residues: Nva–Ser (Nva = norvaline) with an n-propyl side chain and Abu–Ser, (I) (Abu = 2-amino­butyric acid), with an ethyl side chain. Attempts to grow crystals from Nva–Ser were, unfortunately, uniformly unsuccessful, but (I) yielded small crystals of reasonable quality that permitted a single-crystal X-ray diffraction analysis.

Experimental top

Crystal data, data collection and structure refinement details are summarized in Table 1.

Synthesis and crystallization top

The title compound was prepared by solution-phase reaction processes, described in the Supplementary materials [Not available?]. Fine crystals were grown by adding a few drops of di­methyl­formamide to an aqueous solution (10 ml) of (I) (0.275 g), with subsequent slow evaporation at room temperature.

Refinement top

During the review process of this paper, concerns were raised as to whether the complex molecular disorder could in fact be an artifact resulting from crystal twinning. The diffraction patterns at 105 K looked perfectly normal, with no indication of peak splitting, unindexed peaks or other signs of nonmerohedral twinning. It is important to note that we can safely assume the basic packing arrangement and hydrogen-bonding network to be correct, and that, due to prohibitive steric conflict, disorder would also persist in lower symmetry space groups for both Abu and Ser side-chain columns. This was subsequently demonstrated by solving the structure in the monoclinic space group C2 [a = 25.833 (7), b = 5.1328 (15), c = 18.303 (9) Å, β = 134.86 (2)°, Rint = 0.060] with Z' = 2, both molecules showing exactly the same type of disorder, as indicated for the single I4 molecule in Fig. 1, with no improvement in the R factor [= 0.086 for a slightly more crude disorder model for the C-terminal residue than applied for (I)]. Furthermore, a new data set collected with Cu radiation (λ = 1.542 Å) confirmed that the space group is also I4 at room temperature [a = b = 18.3287 (10) and c = 5.1461 (4) Å], thus ruling out the possibilty of a phase transition taking place during cooling from 295 K to the 105 K used for data collection for (I).

N—H and C—H bond lengths were fixed at 0.91 (NH3+), 0.88 (>N—H), 0.98 (CH3), 0.99 (CH2) or 1.00 (CH) Å (default SHELXTL values at 105 K; Sheldrick, 2008), with rotation permitted for the amino group. Uiso values were 1.5Ueq of the carrier atom for hy­droxy, amino and methyl groups, and 1.2Ueq for other H atoms. Heavy-atom disorder was evident for the Abu side chain (two components), as well as for the Ser residue, for which the main-chain atoms, although at short separation, were also included in a disorder model with three components (see Fig. 1). The combination of tetra­gonal symmetry, extensive disorder and a small crystal with rather weak diffraction put pressure on the reflection-to-parameter ratio. In order not to compromise this ratio further, a number of measures were taken to limit the number of refinement parameters: (i) refinement of a single isotropic displacement parameter for atoms C21 and C22, and for atoms C61, C62 and C63; (ii) applying the same set of anisotropic displacement parameters for equivalent main-chain atoms affected by disorder, e.g. N21, N22 and N23; (iii) use of SHELXTL AFIX 83 commands for hy­droxy H atoms, which uses the best staggered position considering the available hydrogen-bond acceptors. As the electron density associated with the three positions for the Ser Cβ atoms was large and diffuse, appropriate restraints were introduced for the geometry of this side chain. In the absence of significant anomalous scattering effects, 865 Friedel pairs were merged.

Results and discussion top

The molecular structure (Fig. 1) and the crystal packing arrangement (Fig. 2d) show that (I) does not belong to the Leu–Ser class, but instead is a close mimic of the structure of Ala–Ala (CSD refcode ALAALA; Fletterick et al., 1970) shown in Fig. 2(a), which has a three-dimensional hydrogen-bonding network and tetra­gonal symmetry (space group I4). Hydro­phobic columns generated by the methyl groups of the N-terminal residues of Ala–Ala are located on regular fourfold rotation axes, while the methyl groups of the C-terminal residues build independent columns with 42 screw symmetry. The former has a series of small voids along the c axis (Fig. 2b). These do not take the shape of a continuous channel, but at high pressure the crystals are nevertheless permeable to O2 (but not to N2; Afonso et al., 2010).

We have previously shown that the tetra­gonal unit cell of Ala–Ala is incompatible with an ethyl side chain at the second residue, as Ala–Abu takes on a completely different crystal-packing arrangement with lower density, both for the hydrate obtained from an aqueous solution (1.282 Mg m-3; Görbitz, 2002) and for the related nonhydrate from a 1,1,1,3,3,3-hexa­fluoro­propan-2-ol solution (1.244 Mg m-3; Görbitz, 2005b). I4 symmetry is, on the other hand, retained for Abu–Ala (XOSHOC; Görbitz, 2002) (Fig. 2c), for which the additional side-chain methyl groups essentially fill the voids of the Ala–Ala structure at the fourfold axes (Fig. 2c). This close packing of ethyl side chains implies the introduction of disorder to avoid steric conflict, with an even distribution between two side-chain conformations (gauche- and gauche+). The same type of disorder occurs for the Abu residue of (I), as shown in Fig. 1 and Fig. 2(d) and in detail in Fig. 3(a). The torsion angles listed in Table 2 reveal, as for Abu–Ala, substantial deviations from idealized staggered gauche conformations at ±60° for N1—C11/C12—C21/C22—C31/C32, suggesting a very crowded environment for the Abu side chain.

The surprising aspect of the structure of (I) is that it exists at all, that is that the densely packed hydro­phobic columns of the second residue in Ala–Ala (Fig. 2a) can in fact adapt to accommodate the significantly larger Ser side chain (Fig. 2c) without disrupting the entire structure. This is rendered possible by a slight increase in unit-cell volume (Table 3), but most of all by a remarkably tight stacking of Ser side chains, resulting in a high-density structure. Furthermore, as seen in Fig. 1, the Ser side chain is disordered over three positions. The major position, with N—C—C—O = gauche-, forms what appears to be a hydrogen-bonded ring in the projection in Fig. 2(d), but actually is a right-handed helix (Fig. 3b). The occupancies of the O21 atoms involved in these chains are sterically limited to 1/2, so half of the serine side chains need to use two other conformations. These are distributed randomly along the fourfold screw axis, as illustrated in Fig. 3(b), and may donate H atoms to main-chain carboxyl­ate acceptors when N—C—C—O is gauche+ [occupancy 0.299 (9), violet atom O22 in all illustrations] or to other Ser OH groups when N—C—C—O is trans [occupancy 0.201 (9), O23 orange]. Hydrogen-bond data are given in Table 4.

In addition to the three structures shown in Fig. 2, Ala–Ser could, from the observations made here, be a potential member of the Ala–Ala group. However, a tetra­gonal polymorph has not been observed, as this dipeptide forms monoclinic crystals with exceptionally high density (1.566 Mg m-3) and a compact three-dimensional hydrogen-bonding pattern (Jones et al., 1978).

In conclusion, in the absence of a crystal structure for Nva–Ser (see above), it appears that Leu-Ser is indeed the sole member of its own class of nanoporous dipeptide structures.

Related literature top

For related literature, see: Afonso et al. (2010); Allen (2002); Fletterick et al. (1970); Görbitz (2002, 2005a, 2005b, 2007); Görbitz et al. (2005, 2006); Johansen et al. (2005); Jones et al. (1978); Sheldrick (2008).

Computing details top

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT-Plus (Bruker, 2007); data reduction: SAINT-Plus (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level. Only main-chain atoms N1, C11/C12 (constrained to have the same set of coordinates), C4 and O1 are unaffected by disorder. In the electronic version of the journal, for the Abu side chain, the two alternative positions, each with occupancy 1/2, are shown in light blue and green, respectively. For the C-terminal part, three alternative side-chain orientations are shown in dark colours for component 1 (occupancy 1/2, atom names Xn1), grey/violet for component 2 [occupancy 0.299 (9)] and light grey/orange for component 3 [occupancy 0.201 (9)], with methylene H atoms omitted. For the main chain only, component 1 is included due to extensive overlap.
[Figure 2] Fig. 2. (a) The unit-cell and molecular packing of Ala–Ala (Fletterick et al., 1970), with the inclusion of symbols for crystallographic symmetry operations. Voids at the fourfold axis, calculated in Mercury (Macrae et al., 2008) using a 1.2 Å probe with 0.5 Å grid spacing, account for approximately 5.8% of the unit-cell volume. (b) Part of the same structure, viewed along the a axis. (c) The crystal packing of Abu–Ala (Görbitz, 2002). The different sizes of the hydrophobic columns generated by Abu and Ala side chains have been highlighted. (d) The crystal packing of (I); the colour coding is as in Fig. 1. Inside the circle are hydrogen bonds between Ser side chains (only component 1 is shown). In all parts, dashed lines indicate hydrogen bonds.
[Figure 3] Fig. 3. (a) The stacking of hydrophobic groups along the regular fourfold axis. A wire-frame representation is used to emphasize the steric conflict leading to the 1:1 disorder described in the text. Some prohibitively short distances (in Å) are indicated by dashed lines (red). (b) The hydrogen bonding (dashed lines) along the 42 screw axis. A right-handed hydrogen-bonded chain formed by the OH groups of component 1 has been highlighted. The directly opposing amino acid must have a different conformation; the sequence shown here (3–3-2–2-3–2 from the top) is just a random example. The colour coding is as in Fig. 1.
(S)-2-[(S)-2-Azaniumylbutanamido]-3-hydroxypropanoate top
Crystal data top
C7H14N2O4Dx = 1.462 Mg m3
Mr = 190.20Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4Cell parameters from 2704 reflections
Hall symbol: I 4θ = 3.1–25.1°
a = 18.335 (7) ŵ = 0.12 mm1
c = 5.141 (2) ÅT = 105 K
V = 1728.1 (12) Å3Needle, colourless
Z = 80.39 × 0.09 × 0.06 mm
F(000) = 816
Data collection top
Bruker APEXII CCD area-detector
diffractometer
862 independent reflections
Radiation source: fine-focus sealed tube780 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.084
Detector resolution: 8.3 pixels mm-1θmax = 25.1°, θmin = 2.2°
Sets of exposures each taken over 0.5° ω rotation scansh = 2121
Absorption correction: multi-scan
(SADABS; Bruker, 2007)
k = 2121
Tmin = 0.788, Tmax = 0.993l = 66
6072 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.080H-atom parameters constrained
wR(F2) = 0.195 w = 1/[σ2(Fo2) + (0.0359P)2 + 9.6883P]
where P = (Fo2 + 2Fc2)/3
S = 1.30(Δ/σ)max < 0.001
862 reflectionsΔρmax = 0.38 e Å3
177 parametersΔρmin = 0.30 e Å3
767 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.014 (3)
Crystal data top
C7H14N2O4Z = 8
Mr = 190.20Mo Kα radiation
Tetragonal, I4µ = 0.12 mm1
a = 18.335 (7) ÅT = 105 K
c = 5.141 (2) Å0.39 × 0.09 × 0.06 mm
V = 1728.1 (12) Å3
Data collection top
Bruker APEXII CCD area-detector
diffractometer
862 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2007)
780 reflections with I > 2σ(I)
Tmin = 0.788, Tmax = 0.993Rint = 0.084
6072 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.080767 restraints
wR(F2) = 0.195H-atom parameters constrained
S = 1.30Δρmax = 0.38 e Å3
862 reflectionsΔρmin = 0.30 e Å3
177 parameters
Special details top

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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
N10.7087 (2)0.6819 (2)0.7119 (15)0.0311 (11)
H10.67250.69730.81970.047*
H20.69910.69670.54660.047*
H30.75200.70120.76500.047*
C110.7132 (3)0.6013 (2)0.7194 (13)0.0211 (10)0.50
H1110.74000.58720.88100.025*0.50
C210.6400 (4)0.5606 (6)0.718 (3)0.0210 (16)*0.50
H21A0.64800.50900.66840.025*0.50
H21B0.60700.58290.58760.025*0.50
C310.6028 (5)0.5647 (6)1.005 (2)0.031 (3)0.50
H31A0.55520.54051.00100.046*0.50
H31B0.59650.61581.05550.046*0.50
H31C0.63440.54011.13150.046*0.50
C120.7132 (3)0.6013 (2)0.7194 (13)0.0211 (10)0.50
H1210.73840.58610.88310.025*0.50
C220.6340 (4)0.5741 (7)0.726 (3)0.0210 (16)*0.50
H22A0.60320.60920.82210.025*0.50
H22B0.63160.52650.81690.025*0.50
C320.6037 (5)0.5651 (7)0.430 (2)0.031 (3)0.50
H32A0.55560.54180.43330.046*0.50
H32B0.63750.53480.32930.046*0.50
H32C0.59970.61330.34830.046*0.50
O10.77388 (19)0.6190 (2)0.3075 (12)0.0296 (9)
C40.7587 (3)0.5762 (3)0.4841 (14)0.0244 (11)
N210.7773 (7)0.5008 (13)0.491 (5)0.0259 (15)0.50
H40.76620.47490.62990.031*0.50
C510.8142 (5)0.4657 (6)0.274 (3)0.0283 (14)0.50
H510.82620.50400.14240.034*0.50
C610.8855 (5)0.4295 (4)0.361 (3)0.035 (2)*0.50
H61A0.87490.39370.49980.042*0.50
H61B0.90690.40270.21180.042*0.50
O210.9372 (4)0.4813 (5)0.454 (2)0.057 (3)0.50
H210.94390.51360.34100.085*0.50
C710.7629 (7)0.4096 (7)0.146 (4)0.0222 (15)0.50
O310.7316 (7)0.4247 (9)0.060 (3)0.031 (2)0.50
O410.7530 (13)0.3497 (8)0.268 (4)0.030 (2)0.50
N220.7773 (10)0.5120 (12)0.480 (5)0.0259 (15)0.299 (9)
H50.76330.48550.61420.031*0.299 (9)
C520.8195 (8)0.4740 (7)0.283 (3)0.0283 (14)0.299 (9)
H520.82550.50780.13220.034*0.299 (9)
C620.8956 (6)0.4535 (10)0.380 (3)0.035 (2)*0.299 (9)
H62A0.91770.41810.25770.042*0.299 (9)
H62B0.92670.49760.38120.042*0.299 (9)
O220.8946 (7)0.4226 (7)0.634 (2)0.042 (4)0.299 (9)
H220.85180.41030.67230.064*0.299 (9)
C720.7775 (12)0.4065 (10)0.187 (4)0.0222 (15)0.299 (9)
O320.7439 (16)0.4090 (12)0.023 (4)0.031 (2)0.299 (9)
O420.7745 (11)0.3518 (8)0.341 (4)0.030 (2)0.299 (9)
N230.770 (2)0.502 (3)0.495 (10)0.0259 (15)0.201 (9)
H60.74700.47700.61600.031*0.201 (9)
C530.8176 (11)0.4623 (13)0.318 (6)0.0283 (14)0.201 (9)
H530.83880.49800.19230.034*0.201 (9)
C630.8806 (12)0.4256 (15)0.464 (4)0.035 (2)*0.201 (9)
H63A0.91420.46360.53050.042*0.201 (9)
H63B0.86090.39860.61540.042*0.201 (9)
O230.9201 (10)0.3765 (10)0.302 (5)0.047 (6)0.201 (9)
H230.92360.39420.15150.070*0.201 (9)
C730.7731 (18)0.4059 (18)0.163 (7)0.0222 (15)0.201 (9)
O330.751 (3)0.421 (3)0.058 (6)0.031 (2)0.201 (9)
O430.762 (3)0.344 (2)0.273 (10)0.030 (2)0.201 (9)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.023 (2)0.033 (2)0.037 (3)0.0007 (17)0.005 (2)0.003 (2)
C110.025 (2)0.027 (2)0.011 (2)0.0015 (17)0.0046 (18)0.000 (2)
C310.037 (5)0.036 (5)0.021 (5)0.004 (4)0.008 (4)0.009 (4)
C120.025 (2)0.027 (2)0.011 (2)0.0015 (17)0.0046 (18)0.000 (2)
C320.028 (5)0.042 (5)0.022 (5)0.009 (4)0.001 (4)0.004 (4)
O10.039 (2)0.0363 (19)0.0131 (18)0.0033 (16)0.0026 (18)0.0036 (17)
C40.026 (2)0.029 (2)0.018 (2)0.0009 (19)0.003 (2)0.003 (2)
N210.033 (3)0.025 (2)0.019 (2)0.002 (2)0.004 (2)0.000 (2)
C510.034 (2)0.027 (2)0.024 (3)0.0016 (18)0.008 (2)0.001 (2)
O210.053 (4)0.053 (5)0.064 (6)0.015 (4)0.012 (5)0.002 (5)
C710.020 (3)0.027 (2)0.020 (3)0.006 (2)0.004 (2)0.000 (2)
O310.035 (5)0.034 (4)0.026 (3)0.003 (4)0.003 (3)0.007 (2)
O410.032 (5)0.026 (2)0.032 (4)0.003 (3)0.003 (3)0.006 (2)
N220.033 (3)0.025 (2)0.019 (2)0.002 (2)0.004 (2)0.000 (2)
C520.034 (2)0.027 (2)0.024 (3)0.0016 (18)0.008 (2)0.001 (2)
O220.047 (6)0.043 (6)0.037 (7)0.001 (5)0.001 (5)0.003 (5)
C720.020 (3)0.027 (2)0.020 (3)0.006 (2)0.004 (2)0.000 (2)
O320.035 (5)0.034 (4)0.026 (3)0.003 (4)0.003 (3)0.007 (2)
O420.032 (5)0.026 (2)0.032 (4)0.003 (3)0.003 (3)0.006 (2)
N230.033 (3)0.025 (2)0.019 (2)0.002 (2)0.004 (2)0.000 (2)
C530.034 (2)0.027 (2)0.024 (3)0.0016 (18)0.008 (2)0.001 (2)
O230.047 (7)0.049 (8)0.044 (9)0.010 (5)0.010 (7)0.002 (7)
C730.020 (3)0.027 (2)0.020 (3)0.006 (2)0.004 (2)0.000 (2)
O330.035 (5)0.034 (4)0.026 (3)0.003 (4)0.003 (3)0.007 (2)
O430.032 (5)0.026 (2)0.032 (4)0.003 (3)0.003 (3)0.006 (2)
Geometric parameters (Å, º) top
N1—C111.480 (6)C61—O211.425 (3)
N1—H10.9100C61—H61A0.9900
N1—H20.9100C61—H61B0.9900
N1—H30.9100O21—H210.8400
C11—C211.535 (7)C71—O311.239 (8)
C11—C41.541 (7)C71—O411.279 (7)
C11—H1111.0000N22—C521.452 (3)
C21—C311.629 (17)N22—H50.8800
C21—H21A0.9900C52—C621.529 (3)
C21—H21B0.9900C52—C721.540 (8)
C31—H31A0.9800C52—H521.0000
C31—H31B0.9800C62—O221.425 (3)
C31—H31C0.9800C62—H62A0.9900
C22—C321.629 (17)C62—H62B0.9900
C22—H22A0.9900O22—H220.8400
C22—H22B0.9900C72—O321.240 (8)
C32—H32A0.9800C72—O421.279 (7)
C32—H32B0.9800N23—C531.454 (3)
C32—H32C0.9800N23—H60.8800
O1—C41.231 (7)C53—C631.532 (3)
C4—N221.226 (19)C53—C731.541 (8)
C4—N231.38 (6)C53—H531.0000
C4—N211.42 (2)C63—O231.426 (3)
N21—C511.454 (3)C63—H63A0.9900
N21—H40.8800C63—H63B0.9900
C51—C611.532 (3)O23—H230.8400
C51—C711.542 (8)C73—O331.239 (8)
C51—H511.0000C73—O431.279 (7)
N1—C11—C21115.9 (6)O21—C61—H61A109.2
N1—C11—C4107.9 (4)C51—C61—H61A109.2
C21—C11—C4108.9 (7)O21—C61—H61B109.2
N1—C11—H111107.9C51—C61—H61B109.2
C21—C11—H111107.9H61A—C61—H61B107.9
C4—C11—H111107.9C61—O21—H21109.5
C11—C21—C31109.8 (9)O31—C71—O41123.2 (7)
C11—C21—H21A109.7O31—C71—C51120.0 (6)
C31—C21—H21A109.7O41—C71—C51116.8 (6)
C11—C21—H21B109.7C4—N22—C52128 (2)
C31—C21—H21B109.7C4—N22—H5115.9
H21A—C21—H21B108.2C52—N22—H5115.9
C21—C31—H31A109.5N22—C52—C62112.1 (3)
C21—C31—H31B109.5N22—C52—C72110.2 (5)
H31A—C31—H31B109.5C62—C52—C72111.3 (5)
C21—C31—H31C109.5N22—C52—H52107.7
H31A—C31—H31C109.5C62—C52—H52107.7
H31B—C31—H31C109.5C72—C52—H52107.7
C32—C22—H22A109.8O22—C62—C52112.5 (4)
C32—C22—H22B109.8O22—C62—H62A109.1
H22A—C22—H22B108.2C52—C62—H62A109.1
C22—C32—H32A109.5O22—C62—H62B109.1
C22—C32—H32B109.5C52—C62—H62B109.1
H32A—C32—H32B109.5H62A—C62—H62B107.8
C22—C32—H32C109.5C62—O22—H22109.5
H32A—C32—H32C109.5O32—C72—O42123.0 (7)
H32B—C32—H32C109.5O32—C72—C52119.9 (6)
N22—C4—O1122.5 (14)O42—C72—C52116.8 (6)
N22—C4—N238 (3)C4—N23—C53124 (4)
O1—C4—N23129 (2)C4—N23—H6118.0
N22—C4—N213.3 (19)C53—N23—H6118.0
O1—C4—N21125.7 (11)N23—C53—C63111.5 (4)
N23—C4—N215 (3)N23—C53—C73109.9 (5)
N22—C4—C11116.7 (14)C63—C53—C73110.9 (5)
O1—C4—C11120.7 (4)N23—C53—H53108.1
N23—C4—C11110 (2)C63—C53—H53108.1
N21—C4—C11113.5 (10)C73—C53—H53108.1
C4—N21—C51121.4 (18)O23—C63—C53111.9 (4)
C4—N21—H4119.3O23—C63—H63A109.2
C51—N21—H4119.3C53—C63—H63A109.2
N21—C51—C61111.5 (4)O23—C63—H63B109.2
N21—C51—C71109.8 (4)C53—C63—H63B109.2
C61—C51—C71110.8 (5)H63A—C63—H63B107.9
N21—C51—H51108.2C63—O23—H23109.5
C61—C51—H51108.2O33—C73—O43123.2 (7)
C71—C51—H51108.2O33—C73—C53120.0 (6)
O21—C61—C51112.1 (4)O43—C73—C53116.8 (6)
N1—C11—C4—N21170.3 (8)C61—C51—C71—O4148.4 (19)
C11—C4—N21—C51174.1 (7)O1—C4—N22—C521 (2)
C4—N21—C51—C71113.0 (12)N23—C4—N22—C52142 (19)
N21—C51—C71—O31102.4 (15)N21—C4—N22—C52165 (27)
N1—C11—C21—C3176.8 (10)C11—C4—N22—C52179.4 (12)
N1—C12—C22—C3287.9 (9)C4—N22—C52—C62110 (2)
N21—C51—C61—O2163.7 (11)C4—N22—C52—C72125 (2)
N22—C52—C62—O2245.3 (13)C72—C52—C62—O2278.6 (12)
N23—C53—C63—O23170 (3)N22—C52—C72—O32101 (3)
C4—C11—C21—C31161.3 (7)C62—C52—C72—O32134 (3)
N1—C11—C4—N22169.4 (12)N22—C52—C72—O4274 (2)
C21—C11—C4—N2264.0 (14)C62—C52—C72—O4251 (2)
N1—C11—C4—O112.2 (6)N22—C4—N23—C5328 (16)
C21—C11—C4—O1114.5 (7)O1—C4—N23—C5315 (4)
N1—C11—C4—N23174.7 (19)N21—C4—N23—C5343 (28)
C21—C11—C4—N2359 (2)C11—C4—N23—C53172.9 (18)
C21—C11—C4—N2163.1 (10)C4—N23—C53—C63118 (3)
N22—C4—N21—C5120 (25)C4—N23—C53—C73119 (3)
O1—C4—N21—C513.3 (15)C73—C53—C63—O2347 (3)
N23—C4—N21—C51123 (30)N23—C53—C73—O3396 (4)
C4—N21—C51—C61123.8 (10)C63—C53—C73—O33140 (4)
C71—C51—C61—O21173.7 (10)N23—C53—C73—O4384 (5)
C61—C51—C71—O31134.1 (15)C63—C53—C73—O4340 (5)
N21—C51—C71—O4175 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O31i0.911.992.862 (15)160
N1—H2···O41ii0.911.982.84 (2)157
N1—H3···O41iii0.911.982.86 (2)163
C11—H111···O1iv1.002.353.238 (6)147
N21—H4···O31iv0.881.952.82 (3)173
O21—H21···O21v0.842.293.081 (6)158
O22—H22···O31iv0.842.613.37 (2)152
O23—H23···O21vi0.842.172.77 (2)129
Symmetry codes: (i) y+1, x, z+1; (ii) y+1, x, z; (iii) y+1/2, x+3/2, z+1/2; (iv) x, y, z+1; (v) y+1/2, x+3/2, z1/2; (vi) y+3/2, x1/2, z1/2.

Experimental details

Crystal data
Chemical formulaC7H14N2O4
Mr190.20
Crystal system, space groupTetragonal, I4
Temperature (K)105
a, c (Å)18.335 (7), 5.141 (2)
V3)1728.1 (12)
Z8
Radiation typeMo Kα
µ (mm1)0.12
Crystal size (mm)0.39 × 0.09 × 0.06
Data collection
DiffractometerBruker APEXII CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2007)
Tmin, Tmax0.788, 0.993
No. of measured, independent and
observed [I > 2σ(I)] reflections
6072, 862, 780
Rint0.084
(sin θ/λ)max1)0.597
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.080, 0.195, 1.30
No. of reflections862
No. of parameters177
No. of restraints767
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.38, 0.30

Computer programs: APEX2 (Bruker, 2007), SAINT-Plus (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Selected torsion angles (º) top
N1—C11—C4—N21170.3 (8)N1—C12—C22—C3287.9 (9)
C11—C4—N21—C51174.1 (7)N21—C51—C61—O2163.7 (11)
C4—N21—C51—C71113.0 (12)N22—C52—C62—O2245.3 (13)
N21—C51—C71—O31102.4 (15)N23—C53—C63—O23170 (3)
N1—C11—C21—C3176.8 (10)
Crystal data for dipeptide structures with I4 symmetry top
ParameterAla–Ala*Abu–Ala**(I)
a, b (Å)17.985 (5)17.9290 (12)18.355 (7)
c (Å)5.154 (3)5.2196 (5)5.141 (2)
V3)1667.11677.8 (2)1728.1 (12)
Dx (Mg m-3)1.2761.3791.462
Notes: (*) Fletterick et al. (1970); (**) Görbitz (2002).
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O31i0.911.992.862 (15)160.3
N1—H2···O41ii0.911.982.84 (2)156.9
N1—H3···O41iii0.911.982.86 (2)163.1
C11—H111···O1iv1.002.353.238 (6)147.1
N21—H4···O31iv0.881.952.82 (3)173.3
O21—H21···O21v0.842.293.081 (6)157.5
O22—H22···O31iv0.842.613.37 (2)152.1
O23—H23···O21vi0.842.172.77 (2)129.3
Symmetry codes: (i) y+1, x, z+1; (ii) y+1, x, z; (iii) y+1/2, x+3/2, z+1/2; (iv) x, y, z+1; (v) y+1/2, x+3/2, z1/2; (vi) y+3/2, x1/2, z1/2.
 

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