Terrein

The fungal metabolite terrein (alternative name: trans-2,3-di­hydroxy-4-propenyl­cyclo­pent-4-enone), C₈H₁₀O₃, forms monoclinic (P2₁) crystals. The mol­ecules form hydrogen-bonded chains, with O...O distances of 2.7115 (16) and 2.8155 (15) Å.

S1. Comment

The discovery of bioactive natural products is greatly facilitated by the opportunity to examine unusual organisms. One such group, which has proven to be a rich source of interesting compounds, is the endophytic fungi. Such fungi are commonly present within the living tissues of plants and often appear to act in a symbiotic fashion with them. Frequently, such endophytes develop host specificity and thus are found nowhere else in nature except with their respective plant host.

As part of our survey of endophytic fungi of the highlands of Papua New Guinea, the fungus Pestalotiopsis microspora was isolated and examined for bioactive components. Previous work has demonstrated that P. microspora from other plant sources produces a variety of bioactive compounds including the anticancer drug taxol (Strobel et al., 1996). Bioassay guided fractionation of a culture solution of P. microspora provided a crystalline solid. X-ray analysis of a suitable crystal established that the isolated material was terrein. Previously terrein has been isolated from fungi of the Aspergillus (Raistrick & Smith, 1953; Misawa et al., 1962; Qureshi et al., 1968, 1976), Penicillum (Grove, 1954) and Phoma (Dunn et al., 1975) genera and exhibits both antibacterial and plant growth inhibitor activity (Kamata et al., 1983; Qureshi et al., 1976). However, no crystal structure of terrein has yet appeared. In order to characterize the hydrogen bonding modes, often crucial to bioactivity, the X-ray analysis was performed.

Crystalline terrein forms a hydrogen-bonding network composed entirely of intermolecular hydrogen bonds. The carbonyl at C1 acts as a hydrogen bond acceptor to the C2 OH in a neighbouring molecule. The C2 OH interacts both at C1 (as described above) and as a hydrogen-bond acceptor to the C3 OH of an adjacent molecule.

S2. Experimental

Samples of P. Microspora were isolated from leaf and stem tissue of a Pandanus sp. using previously described methods (Strobel, et al., 1996). A culture (5 l) of P. microspora was grown on M1D media (Pinkerton & Strobel, 1976) enriched with 1 g l⁻¹ of soytone. After a 15-day incubation (296 K), the fluid was filtered then twice extracted with equal volumes of methylene chloride. Evaporation of methylene chloride gave 250 mg of crude material. Preliminary separation was achieved on a silica gel column using CHCl₃–MeOH (20:1). Fractions containing common materials by TLC analysis (silica, CHCl₃–MeOH, 7:1) were combined and examined for antifungal activity utilizing the plant pathogenic fungus Pythium ultimum as a test organism. The active fraction [R_f = 0.45, silica TLC, (CHCl₃–MeOH, 7:1)] was further purified on silica gel using ethyl acetate–hexane 4:1. Pooling of common fractions provided 55 mg of terrein. Plate like crystals (m.p. 392–395 K) were obtained by slow evaporation of a methanol solution. A suitable crystal was obtained only after cutting a contact twinned crystal parallel to the plane of the plate. Although the lack of suitable anomolous scatterers did not allow determination of absolute stereochemistry, optical rotation, [α] = + 142°, (c = 0.175 g per 100 ml, water), verified that the structure described herein is (+)-terrein (Barton & Miller, 1955).

S3. Refinement

Hydroxy H atoms were located and isotropically refined. Other H atoms were treated as riding (C—H 0.95–1.00 Å) Friedel pairs (1025) were merged and averaged in the data set, since anomalous dispersion effects are negligible.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SIR97 (Altomare et al., 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

(I)

Crystal data

C8H10O3	Dx = 1.328 Mg m^−3
Mr = 154.16	Melting point = 392–395 K
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 4.5377 (2) Å	Cell parameters from 7566 reflections
b = 6.9065 (2) Å	θ = 1.0–32.6°
c = 12.3009 (5) Å	µ = 0.10 mm^−1
β = 90.372 (2)°	T = 200 K
V = 385.50 (3) Å^3	Thin plate, colourless
Z = 2	0.32 × 0.3 × 0.12 mm
F(000) = 164

Data collection

Nonius KappaCCD diffractometer	1344 reflections with I > 2σ(I)
ϕ and ω scans	Rint = 0.016
Absorption correction: multi-scan DENZO-SMN (Otwinowski & Minor, 1997)	θmax = 32.6°, θmin = 4.4°
Tmin = 0.968, Tmax = 0.988	h = −6→6
7566 measured reflections	k = −10→10
1479 independent reflections	l = −18→18

Refinement

Refinement on F^2	H atoms treated by a mixture of independent and constrained refinement
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0429P)^2 + 0.037P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.035	(Δ/σ)max < 0.001
wR(F^2) = 0.090	Δρmax = 0.21 e Å^−3
S = 1.05	Δρmin = −0.16 e Å^−3
1479 reflections	Absolute structure: Flack (1983)
109 parameters	Absolute structure parameter: 0.5 (11)
1 restraint

Special details

Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm (Fox & Holmes, 1966) which effectively corrects for absorption effects. High redundancy data were used in the scaling program hence the 'multi-scan' code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size' command in the SHELXL97 input file.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.4299 (2)	0.46199 (19)	0.50948 (9)	0.0391 (3)
O2	0.5205 (2)	0.21511 (18)	0.32289 (9)	0.0327 (2)
H2	0.566 (5)	0.143 (5)	0.382 (2)	0.064 (7)*
O3	−0.0447 (2)	0.31692 (18)	0.17100 (8)	0.0321 (2)
H3	−0.184 (4)	0.290 (4)	0.2068 (17)	0.040 (5)*
C1	0.2852 (3)	0.4793 (2)	0.42493 (11)	0.0284 (3)
C2	0.2578 (3)	0.3202 (2)	0.33958 (9)	0.0253 (2)
H2A	0.1014	0.2276	0.3633	0.03*
C3	0.1469 (3)	0.4268 (2)	0.23769 (10)	0.0259 (3)
H3A	0.3226	0.4627	0.1933	0.031*
C4	0.0184 (3)	0.6132 (2)	0.28472 (11)	0.0280 (3)
C5	0.1109 (3)	0.6412 (2)	0.38841 (12)	0.0328 (3)
H5	0.067	0.7521	0.431	0.039*
C6	−0.1680 (3)	0.7484 (2)	0.22604 (12)	0.0320 (3)
H6	−0.2538	0.8506	0.2668	0.038*
C7	−0.2295 (3)	0.7422 (2)	0.12017 (12)	0.0331 (3)
H7	−0.1527	0.6379	0.0787	0.04*
C8	−0.4136 (4)	0.8910 (3)	0.06311 (14)	0.0418 (4)
H8A	−0.5711	0.8266	0.0219	0.063*
H8B	−0.2898	0.9654	0.0132	0.063*
H8C	−0.5004	0.9785	0.1168	0.063*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0506 (7)	0.0366 (6)	0.0299 (5)	−0.0021 (6)	−0.0110 (5)	−0.0011 (4)
O2	0.0316 (5)	0.0342 (5)	0.0324 (5)	0.0081 (4)	0.0024 (4)	0.0034 (4)
O3	0.0357 (5)	0.0322 (6)	0.0282 (5)	−0.0042 (5)	−0.0048 (4)	−0.0036 (4)
C1	0.0297 (6)	0.0292 (6)	0.0262 (6)	−0.0026 (5)	0.0007 (4)	−0.0016 (5)
C2	0.0259 (5)	0.0262 (6)	0.0239 (5)	−0.0006 (5)	0.0004 (4)	0.0004 (5)
C3	0.0265 (5)	0.0272 (6)	0.0241 (5)	−0.0014 (5)	−0.0010 (4)	−0.0002 (5)
C4	0.0287 (6)	0.0256 (6)	0.0295 (6)	−0.0005 (5)	−0.0002 (5)	0.0005 (5)
C5	0.0382 (7)	0.0299 (7)	0.0304 (7)	0.0031 (6)	−0.0001 (5)	−0.0055 (5)
C6	0.0359 (7)	0.0265 (7)	0.0338 (7)	0.0037 (6)	−0.0005 (5)	−0.0007 (5)
C7	0.0347 (7)	0.0298 (7)	0.0347 (7)	0.0001 (6)	−0.0015 (5)	0.0024 (6)
C8	0.0483 (9)	0.0375 (9)	0.0394 (8)	0.0024 (7)	−0.0101 (7)	0.0075 (6)

Geometric parameters (Å, º)

O1—C1	1.2320 (17)	C4—C5	1.3541 (19)
O2—C2	1.4117 (16)	C4—C6	1.4494 (19)
O2—H2	0.90 (3)	C5—H5	0.95
O3—C3	1.4127 (16)	C6—C7	1.331 (2)
O3—H3	0.80 (2)	C6—H6	0.95
C1—C5	1.440 (2)	C7—C8	1.496 (2)
C1—C2	1.5243 (19)	C7—H7	0.95
C2—C3	1.5358 (18)	C8—H8A	0.98
C2—H2A	1.00	C8—H8B	0.98
C3—C4	1.528 (2)	C8—H8C	0.98
C3—H3A	1.00
C2—O2—H2	111.0 (15)	C5—C4—C3	111.11 (12)
C3—O3—H3	107.1 (15)	C6—C4—C3	125.25 (11)
O1—C1—C5	128.84 (14)	C4—C5—C1	110.44 (13)
O1—C1—C2	123.52 (14)	C4—C5—H5	124.8
C5—C1—C2	107.62 (11)	C1—C5—H5	124.8
O2—C2—C1	113.92 (11)	C7—C6—C4	125.77 (14)
O2—C2—C3	113.60 (10)	C7—C6—H6	117.1
C1—C2—C3	103.96 (12)	C4—C6—H6	117.1
O2—C2—H2A	108.4	C6—C7—C8	123.35 (15)
C1—C2—H2A	108.4	C6—C7—H7	118.3
C3—C2—H2A	108.4	C8—C7—H7	118.3
O3—C3—C4	115.94 (11)	C7—C8—H8A	109.5
O3—C3—C2	114.41 (12)	C7—C8—H8B	109.5
C4—C3—C2	102.64 (10)	H8A—C8—H8B	109.5
O3—C3—H3A	107.8	C7—C8—H8C	109.5
C4—C3—H3A	107.8	H8A—C8—H8C	109.5
C2—C3—H3A	107.8	H8B—C8—H8C	109.5
C5—C4—C6	123.59 (13)
O1—C1—C2—O2	−38.46 (18)	O3—C3—C4—C6	−41.50 (18)
C5—C1—C2—O2	142.77 (12)	C2—C3—C4—C6	−166.94 (12)
O1—C1—C2—C3	−162.62 (13)	C6—C4—C5—C1	178.33 (12)
C5—C1—C2—C3	18.61 (13)	C3—C4—C5—C1	−4.14 (17)
O2—C2—C3—O3	89.37 (14)	O1—C1—C5—C4	171.88 (14)
C1—C2—C3—O3	−146.26 (11)	C2—C1—C5—C4	−9.44 (16)
O2—C2—C3—C4	−144.19 (11)	C5—C4—C6—C7	169.59 (15)
C1—C2—C3—C4	−19.82 (12)	C3—C4—C6—C7	−7.6 (2)
O3—C3—C4—C5	141.02 (12)	C4—C6—C7—C8	−177.32 (15)
C2—C3—C4—C5	15.57 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1^i	0.90 (3)	1.83 (3)	2.7115 (16)	165 (2)
O3—H3···O2^ii	0.80 (2)	2.03 (2)	2.8155 (15)	168.4 (18)

Symmetry codes: (i) −x+1, y−1/2, −z+1; (ii) x−1, y, z.