An oxazol-5(4H)-one from benzyloxy­carbonyl-(Aib)₄-OH

Benzyl N-[8-(4,4-dimethyl-5-oxo-4,5-dihydrooxazol-2-yl)-2,5,5,8-tetra­methyl-3,6-dioxo-4,7-diazanon-2-yl]­carbamate, C₂₄H₃₄N₄O₆, an oxazol-5(4H)-one from N-α-benzyloxycarbonyl-(Aib)₄-OH (Aib = α-amino­isobutyryl) represents the longest peptide oxazolone so far characterized by X-ray diffraction. The overall geometry of the oxazolone ring compares well with literature data. The Aib(1) and Aib(2) residues are folded into a type III β-bend, while the conformation adopted by Aib(3), preceding the oxazolone moiety, is semi-extended. The disposition of the oxazolone ring relative to the preceding residue is stabilized by C—­H...N and C—H...O intramolecular interactions.

Computing details

Data collection: FEBO (Belletti, 1993); cell refinement: FEBO; data reduction: FEBO; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1998); software used to prepare material for publication: SHELXL97.

benzyl N-[8-(4,4-dimethyl-5-oxooxazol-2-yl)-2,5,5,8-tetramethyl-3,6-dioxo-4,7- diazanon-2-yl]carbamate

Crystal data

C24H34N4O6	Dx = 1.203 Mg m^−3
Mr = 474.55	Melting point: 430 K K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.324 (2) Å	Cell parameters from 48 reflections
b = 25.149 (3) Å	θ = 7–12°
c = 11.753 (2) Å	µ = 0.09 mm^−1
β = 108.00 (5)°	T = 293 K
V = 2621.1 (8) Å^3	Prism, colourless
Z = 4	0.6 × 0.4 × 0.4 mm
F(000) = 1016

Data collection

Philips PW1100 diffractometer	Rint = 0.020
Radiation source: fine-focus sealed tube	θmax = 24.7°, θmin = 4.4°
Graphite monochromator	h = −10→10
θ–2θ scans	k = 0→29
4649 measured reflections	l = 0→13
4427 independent reflections	3 standard reflections every 50 reflections
3058 reflections with I > 2σ(I)	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.132	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0835P)^2] where P = (Fo^2 + 2Fc^2)/3
4427 reflections	(Δ/σ)max = 0.021
315 parameters	Δρmax = 0.15 e Å^−3
3 restraints	Δρmin = −0.22 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
C01	0.0368 (3)	0.43196 (7)	−0.03121 (17)	0.0664 (6)
C02	0.1106 (4)	0.44277 (10)	−0.1132 (2)	0.1002 (9)
H02	0.0551	0.4493	−0.1925	0.120*
C03	0.2652 (6)	0.44402 (13)	−0.0797 (4)	0.1282 (13)
H03	0.3131	0.4523	−0.1361	0.154*
C04	0.3505 (4)	0.43322 (11)	0.0365 (4)	0.1110 (10)
H04	0.4553	0.4340	0.0586	0.133*
C05	0.2793 (3)	0.42144 (10)	0.1184 (2)	0.0908 (7)
H05	0.3351	0.4137	0.1969	0.109*
C06	0.1249 (3)	0.42101 (9)	0.08467 (18)	0.0730 (6)
H06	0.0777	0.4131	0.1417	0.088*
C07	−0.1310 (3)	0.43294 (8)	−0.0658 (2)	0.0888 (8)
H07A	−0.1618	0.4495	−0.0026	0.107*
H07B	−0.1707	0.4541	−0.1378	0.107*
OU	−0.19353 (17)	0.37942 (5)	−0.08716 (11)	0.0736 (4)
C0	−0.2332 (2)	0.35644 (7)	0.00284 (15)	0.0554 (5)
O0	−0.22556 (16)	0.37858 (5)	0.09709 (11)	0.0710 (4)
N1	−0.27910 (16)	0.30639 (5)	−0.02583 (11)	0.0495 (4)
H1	−0.2736	0.2936	−0.0922	0.059*
C1A	−0.33805 (18)	0.27258 (7)	0.05049 (14)	0.0489 (4)
C1B1	−0.3704 (2)	0.21860 (8)	−0.01060 (17)	0.0655 (5)
H1B1	−0.4474	0.2223	−0.0864	0.098*
H1B2	−0.4042	0.1944	0.0390	0.098*
H1B3	−0.2802	0.2050	−0.0229	0.098*
C1B2	−0.4812 (2)	0.29611 (10)	0.0676 (2)	0.0793 (6)
H1B4	−0.4574	0.3290	0.1106	0.119*
H1B5	−0.5222	0.2716	0.1120	0.119*
H1B6	−0.5540	0.3025	−0.0092	0.119*
C1	−0.21910 (19)	0.26420 (6)	0.17437 (14)	0.0459 (4)
O1	−0.25888 (15)	0.25267 (6)	0.26155 (11)	0.0661 (4)
N2	−0.07483 (15)	0.26892 (5)	0.17929 (11)	0.0451 (3)
H2	−0.0557	0.2761	0.1139	0.054*
C2A	0.05393 (19)	0.26267 (7)	0.28876 (14)	0.0494 (4)
C2B1	0.1952 (2)	0.27702 (9)	0.25552 (18)	0.0683 (5)
H2B1	0.2050	0.2533	0.1944	0.102*
H2B2	0.2823	0.2739	0.3249	0.102*
H2B3	0.1869	0.3129	0.2263	0.102*
C2B2	0.0652 (2)	0.20610 (8)	0.33699 (18)	0.0700 (6)
H2B4	−0.0281	0.1965	0.3502	0.105*
H2B5	0.1458	0.2040	0.4111	0.105*
H2B6	0.0849	0.1821	0.2800	0.105*
C2	0.0453 (2)	0.30334 (7)	0.38514 (14)	0.0541 (4)
O2	0.11412 (18)	0.29478 (6)	0.49065 (11)	0.0781 (5)
N3	−0.02424 (16)	0.34978 (6)	0.34785 (12)	0.0545 (4)
H3	−0.0802	0.3525	0.2747	0.065*
C3A	−0.00871 (19)	0.39639 (7)	0.42708 (14)	0.0526 (4)
C3B1	−0.0935 (2)	0.38971 (9)	0.51831 (18)	0.0719 (6)
H3B1	−0.1998	0.3875	0.4774	0.108*
H3B2	−0.0736	0.4197	0.5715	0.108*
H3B3	−0.0605	0.3577	0.5634	0.108*
C3B2	−0.0678 (3)	0.44463 (8)	0.34730 (18)	0.0722 (6)
H3B4	−0.0047	0.4511	0.2979	0.108*
H3B5	−0.0668	0.4752	0.3964	0.108*
H3B6	−0.1691	0.4379	0.2976	0.108*
C3	0.15714 (19)	0.40438 (7)	0.49153 (14)	0.0493 (4)
N4	0.22054 (16)	0.41749 (6)	0.59869 (12)	0.0552 (4)
C4A	0.3832 (2)	0.41893 (8)	0.61541 (17)	0.0624 (5)
C4B1	0.4596 (3)	0.37348 (11)	0.7001 (2)	0.0917 (8)
H4B1	0.4482	0.3794	0.7776	0.137*
H4B2	0.5649	0.3724	0.7071	0.137*
H4B3	0.4134	0.3403	0.6686	0.137*
C4B2	0.4510 (3)	0.47288 (11)	0.6589 (3)	0.0954 (8)
H4B4	0.3973	0.5000	0.6049	0.143*
H4B5	0.5552	0.4733	0.6622	0.143*
H4B6	0.4435	0.4796	0.7373	0.143*
C4	0.3931 (2)	0.40755 (8)	0.49141 (18)	0.0628 (5)
O3	0.24888 (14)	0.39839 (5)	0.41824 (10)	0.0612 (3)
O4	0.49883 (18)	0.40632 (7)	0.45418 (15)	0.0864 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C01	0.1006 (17)	0.0397 (10)	0.0556 (11)	−0.0099 (10)	0.0195 (11)	−0.0006 (8)
C02	0.172 (3)	0.0730 (16)	0.0660 (15)	−0.0173 (18)	0.0520 (18)	−0.0021 (12)
C03	0.186 (4)	0.098 (2)	0.149 (3)	−0.007 (2)	0.122 (3)	−0.005 (2)
C04	0.105 (2)	0.0824 (19)	0.166 (3)	0.0012 (16)	0.071 (2)	−0.002 (2)
C05	0.0877 (18)	0.0897 (18)	0.0955 (17)	−0.0049 (14)	0.0288 (15)	0.0088 (13)
C06	0.0862 (16)	0.0753 (14)	0.0601 (12)	−0.0088 (11)	0.0265 (11)	0.0059 (10)
C07	0.111 (2)	0.0461 (12)	0.0870 (16)	−0.0124 (12)	−0.0021 (14)	0.0169 (11)
OU	0.1014 (11)	0.0525 (8)	0.0535 (8)	−0.0163 (7)	0.0043 (7)	0.0058 (6)
C0	0.0621 (11)	0.0471 (10)	0.0433 (9)	0.0071 (8)	−0.0039 (8)	0.0013 (8)
O0	0.0910 (10)	0.0538 (8)	0.0555 (8)	0.0089 (7)	0.0039 (7)	−0.0129 (6)
N1	0.0605 (9)	0.0459 (8)	0.0360 (7)	−0.0002 (6)	0.0057 (6)	−0.0035 (6)
C1A	0.0438 (9)	0.0538 (10)	0.0457 (9)	0.0018 (7)	0.0088 (7)	−0.0028 (7)
C1B1	0.0680 (13)	0.0635 (12)	0.0602 (11)	−0.0178 (10)	0.0129 (9)	−0.0096 (9)
C1B2	0.0538 (12)	0.1050 (18)	0.0762 (14)	0.0183 (11)	0.0160 (10)	−0.0003 (12)
C1	0.0513 (10)	0.0412 (9)	0.0431 (9)	0.0022 (7)	0.0113 (7)	−0.0019 (7)
O1	0.0730 (9)	0.0796 (9)	0.0504 (7)	0.0060 (7)	0.0260 (6)	0.0120 (6)
N2	0.0463 (8)	0.0501 (8)	0.0348 (7)	0.0014 (6)	0.0066 (6)	−0.0009 (6)
C2A	0.0498 (10)	0.0472 (10)	0.0413 (9)	0.0051 (7)	−0.0004 (7)	−0.0005 (7)
C2B1	0.0501 (11)	0.0804 (14)	0.0638 (12)	0.0045 (10)	0.0022 (9)	−0.0087 (10)
C2B2	0.0773 (14)	0.0524 (11)	0.0640 (12)	0.0134 (10)	−0.0021 (10)	0.0031 (9)
C2	0.0601 (11)	0.0521 (10)	0.0403 (9)	0.0027 (8)	0.0013 (8)	0.0005 (8)
O2	0.1074 (11)	0.0687 (9)	0.0393 (7)	0.0173 (8)	−0.0047 (7)	0.0019 (6)
N3	0.0666 (10)	0.0474 (8)	0.0378 (7)	0.0055 (7)	−0.0011 (6)	−0.0046 (6)
C3A	0.0572 (11)	0.0501 (10)	0.0446 (9)	0.0010 (8)	0.0073 (8)	−0.0095 (7)
C3B1	0.0649 (13)	0.0821 (15)	0.0704 (13)	−0.0102 (11)	0.0235 (10)	−0.0190 (11)
C3B2	0.0885 (15)	0.0526 (11)	0.0623 (12)	0.0160 (10)	0.0041 (11)	−0.0094 (9)
C3	0.0594 (11)	0.0461 (10)	0.0428 (9)	−0.0029 (8)	0.0162 (8)	−0.0042 (7)
N4	0.0575 (9)	0.0581 (9)	0.0457 (8)	−0.0037 (7)	0.0097 (7)	−0.0081 (7)
C4A	0.0554 (11)	0.0664 (12)	0.0589 (11)	−0.0028 (9)	0.0080 (9)	−0.0071 (9)
C4B1	0.0844 (16)	0.112 (2)	0.0667 (14)	0.0209 (14)	0.0066 (12)	0.0070 (13)
C4B2	0.0806 (16)	0.0981 (18)	0.1058 (18)	−0.0279 (14)	0.0263 (14)	−0.0344 (15)
C4	0.0658 (13)	0.0560 (11)	0.0694 (12)	0.0023 (9)	0.0251 (10)	0.0024 (9)
O3	0.0664 (8)	0.0707 (8)	0.0489 (7)	−0.0021 (7)	0.0213 (6)	−0.0057 (6)
O4	0.0754 (10)	0.0940 (12)	0.1024 (12)	0.0049 (8)	0.0458 (9)	0.0041 (9)

Geometric parameters (Å, º)

C01—C02	1.374 (3)	C2A—C2B1	1.528 (3)
C01—C06	1.384 (3)	C2A—C2B2	1.523 (2)
C01—C07	1.490 (3)	C2A—C2	1.547 (2)
C02—C03	1.373 (5)	C2—O2	1.226 (2)
C03—C04	1.378 (5)	C2—N3	1.342 (2)
C04—C05	1.360 (4)	N3—C3A	1.476 (2)
C05—C06	1.370 (3)	C3A—C3	1.510 (3)
C07—OU	1.457 (2)	C3A—C3B1	1.525 (3)
OU—C0	1.353 (2)	C3A—C3B2	1.528 (3)
C0—O0	1.222 (2)	C3—N4	1.259 (2)
C0—N1	1.339 (2)	C3—O3	1.397 (2)
N1—C1A	1.461 (2)	N4—C4A	1.468 (2)
C1A—C1B1	1.522 (2)	C4A—C4	1.516 (3)
C1A—C1B2	1.529 (3)	C4A—C4B2	1.518 (3)
C1A—C1	1.548 (2)	C4A—C4B1	1.539 (3)
C1—O1	1.227 (2)	C4—O4	1.196 (2)
C1—N2	1.334 (2)	C4—O3	1.374 (2)
N2—C2A	1.472 (2)
C02—C01—C06	117.1 (2)	N2—C2A—C2	110.89 (13)
C02—C01—C07	121.1 (2)	C2B1—C2A—C2	105.97 (15)
C06—C01—C07	121.7 (2)	C2B2—C2A—C2	111.00 (14)
C03—C02—C01	120.8 (3)	O2—C2—N3	122.15 (16)
C04—C03—C02	120.9 (3)	O2—C2—C2A	119.66 (15)
C03—C04—C05	119.0 (3)	N3—C2—C2A	117.75 (14)
C06—C05—C04	119.8 (3)	C2—N3—C3A	122.80 (13)
C05—C06—C01	122.3 (2)	N3—C3A—C3	107.93 (14)
OU—C07—C01	111.22 (18)	N3—C3A—C3B1	112.64 (15)
C0—OU—C07	116.83 (16)	C3—C3A—C3B1	109.56 (14)
O0—C0—N1	125.52 (18)	N3—C3A—C3B2	107.27 (13)
O0—C0—OU	124.09 (17)	C3—C3A—C3B2	108.74 (16)
N1—C0—OU	110.38 (15)	C3B1—C3A—C3B2	110.58 (16)
C0—N1—C1A	122.99 (14)	N4—C3—O3	117.23 (15)
N1—C1A—C1B1	106.68 (14)	N4—C3—C3A	128.92 (16)
N1—C1A—C1B2	111.39 (16)	O3—C3—C3A	113.79 (14)
C1B1—C1A—C1B2	110.68 (16)	C3—N4—C4A	106.66 (15)
N1—C1A—C1	111.14 (13)	N4—C4A—C4	103.53 (16)
C1B1—C1A—C1	107.60 (14)	N4—C4A—C4B2	111.88 (17)
C1B2—C1A—C1	109.28 (15)	C4—C4A—C4B2	110.49 (19)
O1—C1—N2	123.08 (16)	N4—C4A—C4B1	108.71 (17)
O1—C1—C1A	120.25 (15)	C4—C4A—C4B1	109.18 (17)
N2—C1—C1A	116.65 (14)	C4B2—C4A—C4B1	112.63 (19)
C1—N2—C2A	124.59 (14)	O4—C4—O3	121.66 (19)
N2—C2A—C2B1	106.61 (14)	O4—C4—C4A	131.2 (2)
N2—C2A—C2B2	111.63 (14)	O3—C4—C4A	107.14 (17)
C2B1—C2A—C2B2	110.50 (16)	C4—O3—C3	105.28 (14)
C06—C01—C02—C03	−1.8 (3)	C2B2—C2A—C2—O2	34.1 (2)
C07—C01—C02—C03	177.2 (2)	N2—C2A—C2—N3	−28.7 (2)
C01—C02—C03—C04	1.6 (4)	C2B1—C2A—C2—N3	86.64 (19)
C02—C03—C04—C05	−0.3 (5)	C2B2—C2A—C2—N3	−153.36 (17)
C03—C04—C05—C06	−0.7 (4)	O2—C2—N3—C3A	7.6 (3)
C04—C05—C06—C01	0.4 (4)	C2A—C2—N3—C3A	−164.78 (16)
C02—C01—C06—C05	0.9 (3)	C2—N3—C3A—C3	48.4 (2)
C07—C01—C06—C05	−178.1 (2)	C2—N3—C3A—C3B1	−72.7 (2)
C02—C01—C07—OU	99.8 (2)	C2—N3—C3A—C3B2	165.42 (18)
C06—C01—C07—OU	−81.2 (3)	N3—C3A—C3—N4	−140.36 (18)
C01—C07—OU—C0	99.2 (2)	C3B1—C3A—C3—N4	−17.4 (3)
C07—OU—C0—O0	3.2 (3)	C3B2—C3A—C3—N4	103.6 (2)
C07—OU—C0—N1	−175.88 (16)	N3—C3A—C3—O3	42.75 (19)
O0—C0—N1—C1A	4.9 (3)	C3B1—C3A—C3—O3	165.72 (15)
OU—C0—N1—C1A	−176.01 (14)	C3B2—C3A—C3—O3	−73.31 (18)
C0—N1—C1A—C1B1	−177.49 (15)	O3—C3—N4—C4A	−3.9 (2)
C0—N1—C1A—C1B2	61.6 (2)	C3A—C3—N4—C4A	179.27 (17)
C0—N1—C1A—C1	−60.5 (2)	C3—N4—C4A—C4	3.89 (19)
N1—C1A—C1—O1	156.08 (15)	C3—N4—C4A—C4B2	122.88 (19)
C1B1—C1A—C1—O1	−87.47 (19)	C3—N4—C4A—C4B1	−112.11 (18)
C1B2—C1A—C1—O1	32.7 (2)	N4—C4A—C4—O4	176.5 (2)
N1—C1A—C1—N2	−25.5 (2)	C4B2—C4A—C4—O4	56.5 (3)
C1B1—C1A—C1—N2	90.98 (17)	C4B1—C4A—C4—O4	−67.8 (3)
C1B2—C1A—C1—N2	−148.80 (16)	N4—C4A—C4—O3	−2.73 (19)
O1—C1—N2—C2A	−2.0 (2)	C4B2—C4A—C4—O3	−122.67 (19)
C1A—C1—N2—C2A	179.64 (14)	C4B1—C4A—C4—O3	112.94 (19)
C1—N2—C2A—C2B1	−174.26 (15)	O4—C4—O3—C3	−178.61 (18)
C1—N2—C2A—C2B2	65.0 (2)	C4A—C4—O3—C3	0.69 (18)
C1—N2—C2A—C2	−59.4 (2)	N4—C3—O3—C4	2.1 (2)
N2—C2A—C2—O2	158.77 (17)	C3A—C3—O3—C4	179.40 (14)
C2B1—C2A—C2—O2	−85.9 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3···O0	0.86	2.21	3.052 (2)	167
N1—H1···O1^i	0.86	2.11	2.9627 (18)	169

Symmetry code: (i) x, −y+1/2, z−1/2.