Boc-AzAla-Ala-OMe

Cécile Abbas; Brigitte Jamart Grégoire; Régis Vanderesse; Claude Didierjean

doi:10.1107/S1600536809045498

. 2009 Nov 14;65(Pt 12):o3079. doi: 10.1107/S1600536809045498

Boc-AzAla-Ala-OMe

Cécile Abbas ^a, Brigitte Jamart Grégoire ^a, Régis Vanderesse ^a, Claude Didierjean ^b,^*

PMCID: PMC2972050 PMID: 21578809

Abstract

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 oligomerization [Abbas et al. (2009 ▶). Tetrahedron Lett. 50, 4158–4160]. The asymmetric unit 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 refinement procedure, see: Flack & Schwarzenbach (1988 ▶). For hydrogen-bond motifs, see: Etter (1990 ▶). graphic file with name e-65-o3079-scheme1.jpg

Experimental

Crystal data

C₁₁H₂₁N₃O₅
M _r = 275.31
Tetragonal,
a = 9.3194 (4) Å
c = 17.4420 (8) Å
V = 1514.86 (12) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 100 K
0.3 × 0.2 × 0.2 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: none
14534 measured reflections
1847 independent reflections
1806 reflections with I > 2σ(I)
R _int = 0.049

Refinement

R[F ² > 2σ(F ²)] = 0.036
wR(F ²) = 0.076
S = 1.12
1847 reflections
178 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.17 e Å⁻³
Δρ_min = −0.13 e Å⁻³

Data collection: COLLECT (Bruker, 2004 ▶); cell refinement: 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 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809045498/dn2501sup1.cif

e-65-o3079-sup1.cif^{(16.8KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809045498/dn2501Isup2.hkl

e-65-o3079-Isup2.hkl^{(89.1KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

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

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

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

supplementary crystallographic information

Comment

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 CH^α 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—N^α (N1—N2) and N^α—C^β (N2—C6) bonds are shorter by about 0.06Å than their homologous bonds in peptides; (ii) the N^α—C' ((N2—C7) bond of 1.392 (3)Å is shorter than the homologous C^α—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 N^α 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.

Experimental

The title compound was prepared from N-tert-butyloxycarbonylaminophtalimide (Abbas et al., 2009), and was crystallized by slow evaporation of a diethyl ether solution.