(E)-17β,19-Epoxy­methano-17,23,24-tridemethyl-4-nor-5β,18α-olean-3-one oxime

Anna Froelich; Oxana B Kazakova; Genrikh Tolstikov; Andrzej K Gzella

doi:10.1107/S1600536809016675

. 2009 May 14;65(Pt 6):o1262. doi: 10.1107/S1600536809016675

(E)-17β,19-Epoxymethano-17,23,24-tridemethyl-4-nor-5β,18α-olean-3-one oxime

Anna Froelich ^a, Oxana B Kazakova ^b, Genrikh Tolstikov ^b, Andrzej K Gzella ^a,^*

PMCID: PMC2969752 PMID: 21583127

Abstract

In the pentacyclic triterpenoide skeleton of the title molecule, C₂₇H₄₃NO₂ [systematic name: (3E,3aS,5aR,5bR,7aR,11R,11aR,11bR,13aR,13bR)-5a,5b,10,10,13b-pentamethylicosahydro-1H-11,7a-(epoxymethano)cyclopenta[a]chrysen-3-one oxime], the five-membered ring A has an envelope conformation, while the six-membered rings B–E adopt chair conformations. Rings A and B are cis-fused. The hydroximino group has an E configuration. Strong intermolecular O—H⋯O hydrogen bonds link the molecules into helical chains.

Related literature

For the syntheses of related compounds, see: Medvedeva et al. (2004 ▶, 2006 ▶); Gzella et al. (1997 ▶, 1998 ▶); Zaprutko (1995 ▶, 1997 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶). For puckering parameters, see: Cremer & Pople (1975 ▶); Spek (2009 ▶).

Experimental

Crystal data

C₂₇H₄₃NO₂
M _r = 413.62
Orthorhombic,
a = 12.5887 (16) Å
b = 13.2550 (11) Å
c = 14.5355 (12) Å
V = 2425.4 (4) Å³
Z = 4
Cu Kα radiation
μ = 0.53 mm⁻¹
T = 293 K
0.40 × 0.22 × 0.13 mm

Data collection

Kuma Diffraction KM-4 diffractometer
Absorption correction: none
4994 measured reflections
2610 independent reflections
2240 reflections with I > 2σ(I)
R _int = 0.037
3 standard reflections every 100 reflections intensity decay: 2.3%

Refinement

R[F ² > 2σ(F ²)] = 0.031
wR(F ²) = 0.094
S = 1.06
2610 reflections
281 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.12 e Å⁻³
Δρ_min = −0.12 e Å⁻³

Data collection: KM-4 Software (Kuma Diffraction, 1996 ▶); cell refinement: KM-4 Software; data reduction: KM-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809016675/fb2138sup1.cif

e-65-o1262-sup1.cif^{(27.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809016675/fb2138Isup2.hkl

e-65-o1262-Isup2.hkl^{(128.2KB, 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
O1—H1⋯O2ⁱ	0.87 (3)	1.93 (3)	2.782 (2)	164 (3)

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Symmetry code: (i) Inline graphic .

supplementary crystallographic information

Comment

One of the steps in our synthesis of the title compound, (E)-17β,19-epoxymethano-17,23,24-tridemethyl-4-nor-5β,18α-olean-3-one oxime (Scheme 1; Fig. 3 - (IV)), from allobetulin (Fig. 3 - (I)) involved ozonolysis of the intermediate δ-apoallobetulin, Fig. 3 - (II), to give 17β,19-epoxymethano-17,23,24-tridemethyl-4-nor-5β,18α-olean-3-one (Fig. 3 - (III)) as the transformation product with a cis-junction between the A/B rings. It should be mentioned that synthetic conversions to new derivatives with altered junction of A/B rings are rarely observed in triterpenoids of the oleanane group [Zaprutko (1995, 1997); Gzella et al. (1997); Gzella et al. (1998); Medvedeva et al. (2004)].

The X-ray structure determination of the title compound was carried out in order to confirm its spatial structure that had been proposed on the basis of spectroscopic data by Medvedeva et al. (2004).

The results obtained for the title compound confirm the cis-junction of A/B rings. The corresponding interplanar angle between the least-squares planes of the A/B rings is 71.85 (8)°. The H atom at the C5 asymmetric centre exhibits β-orientation and occupies a pseudo-axial position with respect to the A ring and an equatorial position to the B ring [the angles of the H5—C5 bond vector to the Cremer & Pople A and B ring plane normals are 9.60 (9) and 64.05 (7)°, respectively (Cremer & Pople, 1975; Spek, 2009)]. The torsion angle H5—C5—C10—C25 of 38° reveals a halfway conformation between synperiplanar and synclinal for bonds H5—C5 and C10—C25.

In the molecule the six-membered rings B–E of the pentacyclic ring system are trans-fused as in allobetuline. The dihedral angles between the least-squares planes of these rings are B/C 7.09 (10), C/D 0.80 (10), D/E 14.95 (9)°.

In the title structure, each of the six-membered rings B–E has a differently distorted chair conformation, whereas both five-membered rings, i.e. the carbocyclic ring A and the heterocyclic ring C17\C18\C19\O2\C28 including epoxymethylene group, assume envelope conformations. The respective puckering parameters (Cremer & Pople, 1975) are Q = 0.373 (2) Å, Φ = 147.1 (4)° and Q = 0.470 (2)Å, Φ = 253.2 (2)°.

The hydroximino function in C3 position has the E configuration. The value of the torsion angle O1—N1—C3—C5 is -179.80 (18)°.

The molecular packing is stabilized by O1—H···O2ⁱ hydrogen bonds (Tab. 1). The hydroxyl hydrogen is donated to the remote-ring epoxy O atom from the neighbour molecule. These hydrogen bonds link the molecules into helical chains which proceed in the c direction (Fig. 2).

Experimental

The title compound was obtained according to the procedure described by Medvedeva et al. (2004). Single colourless needle-crystals suitable for analysis were grown from ethanol by slow evaporation at room temperature.