Isolation, evaluation of bioactivity and structure determination of amethinol A, a prototypic amethane diterpene from Isodon amethystoides bearing a six/five/seven-membered carbon-ring system

We report the isolation of a novel diterpene, designated as `a­methane', from Isodon amethystoides (Lamiaceae). The diterpene [amethinol A; systematic name: (4aR,4bR,7R,10aS)-4b,7-dihy­droxy-7-isopropyl-1,1-dimethyl-9-oxo­do­deca­hydro­benzo[a]azulene-4a(2H)-carb­oxy­lic acid], possesses a unique skeleton containing a six/five/seven-membered tricyclic system. Inter­molecular O—H...O close contacts were found to the carboxyl, carbonyl and hy­droxy groups, connecting mol­ecules into a two-dimensional structure. A possible biosynthetic pathway has been proposed. In addition, the compound was evaluated for its biological activities against different disease targets, and was found to significantly attenuate RORγt-dependent autoimmune responses.

Computing details

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

(4aR,4 bR,7R,10aS)-4 b,7-Dihydroxy-7-isopropyl-1,1-dimethyl-9-oxododecahydrobenzo[a]azulene-4a(2H)-carboxylic acid

Crystal data

C20H32O5	Dx = 1.223 Mg m^−3
Mr = 352.45	Cu Kα radiation, λ = 1.54178 Å
Orthorhombic, P212121	Cell parameters from 3751 reflections
a = 6.4641 (2) Å	θ = 5.6–48.6°
b = 11.6518 (4) Å	µ = 0.70 mm^−1
c = 25.4249 (9) Å	T = 170 K
V = 1914.96 (11) Å^3	Block, colourless
Z = 4	0.28 × 0.15 × 0.12 mm
F(000) = 768

Data collection

Bruker APEXII CCD diffractometer	3630 reflections with I > 2σ(I)
φ and ω scan	Rint = 0.032
Absorption correction: multi-scan (SADABS; Bruker, 2012)	θmax = 71.9°, θmin = 4.2°
Tmin = 0.722, Tmax = 0.786	h = −7→7
24714 measured reflections	k = −13→12
3648 independent reflections	l = −29→30

Refinement

Refinement on F^2	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.028	w = 1/[σ^2(Fo^2) + (0.0418P)^2 + 0.3285P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.074	(Δ/σ)max = 0.001
S = 1.05	Δρmax = 0.23 e Å^−3
3648 reflections	Δρmin = −0.14 e Å^−3
242 parameters	Absolute structure: Flack x determined using 1495 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
0 restraints	Absolute structure parameter: 0.04 (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.

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

	x	y	z	Uiso*/Ueq
O2	0.94217 (16)	0.28421 (10)	0.28036 (4)	0.0226 (2)
H2	0.963 (4)	0.214 (2)	0.2739 (9)	0.042 (6)*
O3	0.30306 (18)	0.35567 (9)	0.31740 (5)	0.0273 (3)
H3	0.179 (4)	0.335 (2)	0.3103 (9)	0.045 (6)*
O5	0.55585 (18)	0.42514 (10)	0.16027 (5)	0.0284 (3)
H5	0.576 (4)	0.494 (2)	0.1522 (9)	0.048 (7)*
O4	0.31887 (18)	0.17124 (9)	0.33942 (5)	0.0302 (3)
O1	0.9565 (2)	0.57373 (10)	0.25697 (5)	0.0359 (3)
C8	0.8617 (2)	0.49022 (13)	0.24168 (6)	0.0226 (3)
C13	0.7537 (2)	0.36813 (13)	0.15861 (6)	0.0239 (3)
C20	0.4053 (2)	0.26256 (13)	0.33269 (6)	0.0222 (3)
C5	0.7133 (2)	0.38684 (13)	0.36756 (6)	0.0233 (3)
H5A	0.8674	0.3794	0.3681	0.028*
C10	0.6389 (2)	0.27869 (12)	0.33756 (6)	0.0207 (3)
C1	0.7326 (3)	0.17358 (13)	0.36456 (6)	0.0251 (3)
H1A	0.8853	0.1764	0.3617	0.030*
H1B	0.6839	0.1029	0.3468	0.030*
C14	0.9149 (2)	0.44040 (13)	0.18854 (6)	0.0241 (3)
H14A	1.0396	0.3921	0.1931	0.029*
H14B	0.9547	0.5051	0.1654	0.029*
C7	0.6936 (2)	0.43776 (12)	0.27520 (6)	0.0208 (3)
H7	0.5592	0.4508	0.2567	0.025*
C6	0.6729 (3)	0.48890 (13)	0.33102 (6)	0.0247 (3)
H6A	0.7760	0.5504	0.3368	0.030*
H6B	0.5326	0.5206	0.3367	0.030*
C9	0.7232 (2)	0.30567 (12)	0.28054 (6)	0.0195 (3)
C11	0.6197 (2)	0.23782 (13)	0.23618 (6)	0.0226 (3)
H11A	0.4744	0.2638	0.2331	0.027*
H11B	0.6171	0.1558	0.2463	0.027*
C12	0.7222 (3)	0.24793 (13)	0.18195 (6)	0.0250 (3)
H12A	0.6380	0.2031	0.1567	0.030*
H12B	0.8594	0.2105	0.1841	0.030*
C4	0.6520 (3)	0.39262 (15)	0.42607 (6)	0.0302 (4)
C2	0.6694 (3)	0.17070 (15)	0.42285 (7)	0.0319 (4)
H2A	0.5176	0.1608	0.4254	0.038*
H2B	0.7357	0.1041	0.4402	0.038*
C15	0.8242 (3)	0.36049 (15)	0.10016 (6)	0.0325 (4)
H15	0.8295	0.4411	0.0868	0.039*
C3	0.7326 (3)	0.28090 (16)	0.45154 (6)	0.0349 (4)
H3A	0.8855	0.2844	0.4531	0.042*
H3B	0.6808	0.2770	0.4881	0.042*
C18	0.4185 (3)	0.40647 (16)	0.43549 (7)	0.0373 (4)
H18A	0.3671	0.4721	0.4153	0.056*
H18B	0.3930	0.4195	0.4730	0.056*
H18C	0.3466	0.3367	0.4242	0.056*
C19	0.7637 (4)	0.49480 (18)	0.45147 (7)	0.0443 (5)
H19A	0.9117	0.4909	0.4433	0.066*
H19B	0.7445	0.4922	0.4897	0.066*
H19C	0.7064	0.5666	0.4377	0.066*
C17	0.6691 (4)	0.29680 (18)	0.06540 (7)	0.0468 (5)
H17A	0.6767	0.2143	0.0727	0.070*
H17B	0.7020	0.3107	0.0283	0.070*
H17C	0.5290	0.3246	0.0729	0.070*
C16	1.0403 (4)	0.3110 (2)	0.09255 (8)	0.0511 (6)
H16A	1.1410	0.3585	0.1114	0.077*
H16B	1.0744	0.3102	0.0550	0.077*
H16C	1.0445	0.2325	0.1063	0.077*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.0176 (5)	0.0180 (6)	0.0320 (5)	0.0018 (4)	−0.0007 (4)	0.0001 (4)
O3	0.0180 (6)	0.0220 (6)	0.0420 (6)	0.0006 (4)	−0.0023 (5)	0.0025 (4)
O5	0.0272 (6)	0.0225 (6)	0.0354 (6)	0.0028 (5)	−0.0040 (5)	0.0033 (5)
O4	0.0235 (6)	0.0219 (6)	0.0453 (7)	−0.0047 (5)	−0.0011 (5)	0.0043 (5)
O1	0.0467 (7)	0.0299 (6)	0.0311 (6)	−0.0201 (6)	−0.0010 (5)	0.0007 (5)
C8	0.0219 (7)	0.0176 (7)	0.0284 (7)	−0.0004 (6)	−0.0055 (6)	0.0037 (6)
C13	0.0258 (7)	0.0194 (7)	0.0266 (7)	0.0009 (6)	−0.0009 (6)	0.0007 (6)
C20	0.0216 (7)	0.0188 (7)	0.0261 (7)	0.0002 (6)	0.0006 (6)	−0.0008 (6)
C5	0.0209 (7)	0.0216 (7)	0.0276 (8)	−0.0022 (6)	−0.0007 (6)	−0.0020 (6)
C10	0.0194 (7)	0.0166 (7)	0.0262 (7)	−0.0006 (5)	−0.0014 (6)	0.0012 (6)
C1	0.0236 (8)	0.0219 (8)	0.0298 (8)	0.0013 (6)	−0.0019 (6)	0.0038 (6)
C14	0.0241 (7)	0.0192 (7)	0.0290 (7)	−0.0013 (6)	0.0013 (6)	0.0025 (6)
C7	0.0193 (7)	0.0155 (7)	0.0275 (7)	0.0004 (6)	−0.0011 (6)	0.0000 (5)
C6	0.0267 (8)	0.0175 (7)	0.0298 (8)	−0.0018 (6)	0.0025 (6)	−0.0028 (6)
C9	0.0166 (7)	0.0156 (7)	0.0262 (7)	0.0003 (5)	−0.0009 (6)	0.0004 (5)
C11	0.0241 (7)	0.0167 (7)	0.0272 (7)	−0.0020 (6)	−0.0023 (6)	0.0004 (6)
C12	0.0318 (8)	0.0177 (7)	0.0254 (7)	−0.0007 (6)	−0.0031 (6)	−0.0004 (6)
C4	0.0359 (9)	0.0282 (8)	0.0265 (8)	−0.0031 (7)	0.0012 (7)	−0.0015 (6)
C2	0.0362 (9)	0.0284 (9)	0.0311 (8)	0.0010 (7)	−0.0016 (7)	0.0093 (6)
C15	0.0435 (10)	0.0259 (8)	0.0281 (8)	−0.0022 (8)	0.0025 (7)	0.0021 (6)
C3	0.0395 (10)	0.0385 (10)	0.0268 (8)	−0.0007 (8)	−0.0034 (7)	0.0033 (7)
C18	0.0434 (10)	0.0351 (10)	0.0334 (9)	0.0008 (8)	0.0121 (8)	−0.0010 (7)
C19	0.0610 (13)	0.0410 (10)	0.0309 (9)	−0.0094 (10)	0.0001 (9)	−0.0095 (8)
C17	0.0684 (14)	0.0457 (11)	0.0262 (8)	−0.0134 (10)	−0.0033 (9)	−0.0011 (8)
C16	0.0549 (13)	0.0580 (13)	0.0403 (11)	0.0074 (11)	0.0172 (10)	−0.0049 (10)

Geometric parameters (Å, º)

O2—H2	0.84 (3)	C9—C11	1.531 (2)
O2—C9	1.4377 (18)	C11—H11A	0.9900
O3—H3	0.86 (3)	C11—H11B	0.9900
O3—C20	1.3285 (19)	C11—C12	1.534 (2)
O5—H5	0.84 (3)	C12—H12A	0.9900
O5—C13	1.4417 (19)	C12—H12B	0.9900
O4—C20	1.2138 (19)	C4—C3	1.544 (2)
O1—C8	1.214 (2)	C4—C18	1.537 (3)
C8—C14	1.510 (2)	C4—C19	1.535 (3)
C8—C7	1.510 (2)	C2—H2A	0.9900
C13—C14	1.541 (2)	C2—H2B	0.9900
C13—C12	1.535 (2)	C2—C3	1.532 (3)
C13—C15	1.557 (2)	C15—H15	1.0000
C20—C10	1.527 (2)	C15—C17	1.529 (3)
C5—H5A	1.0000	C15—C16	1.523 (3)
C5—C10	1.549 (2)	C3—H3A	0.9900
C5—C6	1.531 (2)	C3—H3B	0.9900
C5—C4	1.541 (2)	C18—H18A	0.9800
C10—C1	1.529 (2)	C18—H18B	0.9800
C10—C9	1.580 (2)	C18—H18C	0.9800
C1—H1A	0.9900	C19—H19A	0.9800
C1—H1B	0.9900	C19—H19B	0.9800
C1—C2	1.538 (2)	C19—H19C	0.9800
C14—H14A	0.9900	C17—H17A	0.9800
C14—H14B	0.9900	C17—H17B	0.9800
C7—H7	1.0000	C17—H17C	0.9800
C7—C6	1.545 (2)	C16—H16A	0.9800
C7—C9	1.557 (2)	C16—H16B	0.9800
C6—H6A	0.9900	C16—H16C	0.9800
C6—H6B	0.9900
C9—O2—H2	109.0 (17)	C9—C11—C12	115.71 (13)
C20—O3—H3	107.7 (16)	H11A—C11—H11B	107.4
C13—O5—H5	107.4 (18)	C12—C11—H11A	108.4
O1—C8—C14	118.68 (15)	C12—C11—H11B	108.4
O1—C8—C7	120.45 (14)	C13—C12—H12A	107.7
C14—C8—C7	120.88 (13)	C13—C12—H12B	107.7
O5—C13—C14	109.49 (12)	C11—C12—C13	118.36 (13)
O5—C13—C12	106.94 (13)	C11—C12—H12A	107.7
O5—C13—C15	108.30 (13)	C11—C12—H12B	107.7
C14—C13—C15	107.74 (13)	H12A—C12—H12B	107.1
C12—C13—C14	113.42 (13)	C5—C4—C3	106.34 (14)
C12—C13—C15	110.84 (13)	C18—C4—C5	114.05 (14)
O3—C20—C10	114.53 (13)	C18—C4—C3	110.75 (15)
O4—C20—O3	121.89 (14)	C19—C4—C5	108.61 (14)
O4—C20—C10	123.48 (14)	C19—C4—C3	108.59 (15)
C10—C5—H5A	104.2	C19—C4—C18	108.36 (16)
C6—C5—H5A	104.2	C1—C2—H2A	109.3
C6—C5—C10	106.26 (12)	C1—C2—H2B	109.3
C6—C5—C4	120.52 (13)	H2A—C2—H2B	107.9
C4—C5—H5A	104.2	C3—C2—C1	111.69 (14)
C4—C5—C10	115.53 (13)	C3—C2—H2A	109.3
C20—C10—C5	116.55 (12)	C3—C2—H2B	109.3
C20—C10—C1	109.24 (12)	C13—C15—H15	106.3
C20—C10—C9	106.91 (12)	C17—C15—C13	112.79 (15)
C5—C10—C9	100.54 (11)	C17—C15—H15	106.3
C1—C10—C5	107.90 (12)	C16—C15—C13	114.29 (15)
C1—C10—C9	115.77 (12)	C16—C15—H15	106.3
C10—C1—H1A	109.6	C16—C15—C17	110.15 (17)
C10—C1—H1B	109.6	C4—C3—H3A	108.6
C10—C1—C2	110.18 (13)	C4—C3—H3B	108.6
H1A—C1—H1B	108.1	C2—C3—C4	114.65 (14)
C2—C1—H1A	109.6	C2—C3—H3A	108.6
C2—C1—H1B	109.6	C2—C3—H3B	108.6
C8—C14—C13	119.87 (13)	H3A—C3—H3B	107.6
C8—C14—H14A	107.4	C4—C18—H18A	109.5
C8—C14—H14B	107.4	C4—C18—H18B	109.5
C13—C14—H14A	107.4	C4—C18—H18C	109.5
C13—C14—H14B	107.4	H18A—C18—H18B	109.5
H14A—C14—H14B	106.9	H18A—C18—H18C	109.5
C8—C7—H7	107.3	H18B—C18—H18C	109.5
C8—C7—C6	115.14 (13)	C4—C19—H19A	109.5
C8—C7—C9	111.16 (12)	C4—C19—H19B	109.5
C6—C7—H7	107.3	C4—C19—H19C	109.5
C6—C7—C9	108.17 (12)	H19A—C19—H19B	109.5
C9—C7—H7	107.3	H19A—C19—H19C	109.5
C5—C6—C7	104.06 (12)	H19B—C19—H19C	109.5
C5—C6—H6A	110.9	C15—C17—H17A	109.5
C5—C6—H6B	110.9	C15—C17—H17B	109.5
C7—C6—H6A	110.9	C15—C17—H17C	109.5
C7—C6—H6B	110.9	H17A—C17—H17B	109.5
H6A—C6—H6B	109.0	H17A—C17—H17C	109.5
O2—C9—C10	107.92 (12)	H17B—C17—H17C	109.5
O2—C9—C7	107.00 (12)	C15—C16—H16A	109.5
O2—C9—C11	109.75 (12)	C15—C16—H16B	109.5
C7—C9—C10	103.55 (11)	C15—C16—H16C	109.5
C11—C9—C10	115.00 (12)	H16A—C16—H16B	109.5
C11—C9—C7	113.13 (12)	H16A—C16—H16C	109.5
C9—C11—H11A	108.4	H16B—C16—H16C	109.5
C9—C11—H11B	108.4
O2—C9—C11—C12	−48.56 (17)	C1—C10—C9—C7	−152.65 (13)
O3—C20—C10—C5	47.36 (18)	C1—C10—C9—C11	83.42 (16)
O3—C20—C10—C1	169.94 (12)	C1—C2—C3—C4	54.8 (2)
O3—C20—C10—C9	−64.09 (15)	C14—C8—C7—C6	173.36 (13)
O5—C13—C14—C8	45.65 (18)	C14—C8—C7—C9	49.92 (18)
O5—C13—C12—C11	−52.52 (18)	C14—C13—C12—C11	68.28 (18)
O5—C13—C15—C17	−58.06 (18)	C14—C13—C15—C17	−176.41 (15)
O5—C13—C15—C16	175.10 (15)	C14—C13—C15—C16	56.76 (19)
O4—C20—C10—C5	−136.33 (15)	C7—C8—C14—C13	23.1 (2)
O4—C20—C10—C1	−13.8 (2)	C7—C9—C11—C12	70.86 (17)
O4—C20—C10—C9	112.22 (16)	C6—C5—C10—C20	−73.26 (16)
O1—C8—C14—C13	−156.69 (15)	C6—C5—C10—C1	163.47 (13)
O1—C8—C7—C6	−6.8 (2)	C6—C5—C10—C9	41.81 (15)
O1—C8—C7—C9	−130.28 (15)	C6—C5—C4—C3	−175.00 (15)
C8—C7—C6—C5	−119.38 (14)	C6—C5—C4—C18	62.6 (2)
C8—C7—C9—O2	33.29 (16)	C6—C5—C4—C19	−58.3 (2)
C8—C7—C9—C10	147.15 (12)	C6—C7—C9—O2	−94.05 (14)
C8—C7—C9—C11	−87.70 (15)	C6—C7—C9—C10	19.82 (15)
C20—C10—C1—C2	−70.13 (17)	C6—C7—C9—C11	144.96 (13)
C20—C10—C9—O2	−161.41 (12)	C9—C10—C1—C2	169.16 (13)
C20—C10—C9—C7	85.39 (13)	C9—C7—C6—C5	5.64 (16)
C20—C10—C9—C11	−38.54 (16)	C9—C11—C12—C13	−55.38 (19)
C5—C10—C1—C2	57.48 (16)	C12—C13—C14—C8	−73.70 (18)
C5—C10—C9—O2	76.47 (13)	C12—C13—C15—C17	58.96 (19)
C5—C10—C9—C7	−36.74 (13)	C12—C13—C15—C16	−67.9 (2)
C5—C10—C9—C11	−160.67 (12)	C4—C5—C10—C20	63.25 (18)
C5—C4—C3—C2	−51.34 (19)	C4—C5—C10—C1	−60.02 (17)
C10—C5—C6—C7	−29.94 (16)	C4—C5—C10—C9	178.32 (13)
C10—C5—C4—C3	55.08 (18)	C4—C5—C6—C7	−163.82 (13)
C10—C5—C4—C18	−67.28 (19)	C15—C13—C14—C8	163.23 (13)
C10—C5—C4—C19	171.78 (14)	C15—C13—C12—C11	−170.37 (14)
C10—C1—C2—C3	−56.66 (19)	C18—C4—C3—C2	73.09 (19)
C10—C9—C11—C12	−170.44 (12)	C19—C4—C3—C2	−168.04 (16)
C1—C10—C9—O2	−39.44 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1^i	0.84 (3)	1.89 (3)	2.7101 (17)	165 (2)
O3—H3···O2^ii	0.86 (3)	1.81 (3)	2.6499 (16)	166 (2)
O5—H5···O4^iii	0.84 (3)	2.18 (3)	2.9797 (17)	158 (2)

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