The absolute configuration of 1-epialexine hemihydrate

The absolute and relative configurations of 1-epialexine are established by X-ray crystallographic analysis, giving (1S,2R,3R,7S,7aS)-1,2,7-trihydroxy-3-(hydroxy­meth­yl)pyrrolizidine. The compound crystallizes as the hemihydrate C₈H₁₅NO₄·0.5H₂O, with hydrogen bonds holding the water mol­ecule in a hydro­philic pocket between epialexine bilayers. In addition, a comparison was made between results obtained from examination of the Bijvoet pairs from data sets collected using molybdenum and copper radiation.

S1. Comment

A new polyhydroxylated pyrrolizidine alkaloid, 1-epialexine, (I), has been isolated from the stems of Castanospermum australe. Alexine, (II), isolated from Alexa leiopetala (Nash et al., 1988), was the first example of a class of 3-hydroxymethyltrihydroxypyrrolizidines, (IV), known as alexines; they possess five chiral centers that give rise to 32 stereoisomers. Australine, (III), which is epimeric at C-7a, was isolated from Castanospermum australe (Molyneux et al., 1988) and shown to inhibit various glucosidases (Tropea et al., 1989). Subsequently other diastereomeric natural products have been isolated (Harris et al., 1989; Nash et al., 1990; Kato et al., 1999, 2007).

The alexines can be regarded as iminosugar analogues which have considerable potential as therapeutic agents (Asano et al., 2001; Watson et al., 2001). The analysis of the structures of alexines is not simple (Wormald et al., 1998; Kato et al., 2003), and confirmation of structure by X-ray crystallographic analysis is essential to ensure that structures are properly reported. Because of the biological activity of the alexines, considerable effort in synthesizing both natural and unnatural stereoisomers has been expended (Choi et al., 1991; Fleet et al., 1988; Takahashi et al., 2008; Trost et al., 2007; Kumar & Pinto, 2006).

The title compound was found to crystallize in the monoclinic space group C2 as the hemihydrate (Fig. 1). The water molecule was found to be well ordered, occupying a position on the twofold axis and acting as a hydrogen-bond acceptor for the hydroxy group O9/H91 and its twofold-related counterpart. The unique water H atom was clearly visible in the difference map hydrogen bonding to atom N4 of a neighbouring 1-epialexine molecule. As a result of these interactions, the O atom of the water molecule occupies a position at the centre of a hydrogen-bonded tetrahedron (Fig. 2). In addition to these interactions, there are a number of other intermolecular strong O—H···O hydrogen bonds (Table 1). These hydrogen bonds lead to the formation of sheets of epialexine molecules which extend along the bc plane. These sheets can be viewed as having a hydrophobic and a hydrophilic side, with all the hydrogen-bonding interactions on the hydrophilic side. The hydrogen bonds connect together pairs of layers with the water molecules in the middle. Thus (I) forms a layered structure of the form ABA–ABA where B represents the hydrophilic–water component (Fig. 3).

The structure was initially determined using Mo Kα radiation on a Nonius Kappa CCD diffractometer. Freidel pairs were measured and the Flack (1983) x parameter refined (Table 2) using the CRYSTALS software (Betteridge et al., 2003). The Flack x parameter was outside the conventionally accepted range with a very large s.u., rendering it essentially meaningless. However, examination of the Bijvoet pairs was carried out within CRYSTALS, and this gave the Hooft y parameter as -0.66 (41) with G = 2.31 (82). This gave the probability that the absolute configuration was correct as greater than 99% assuming the material to be enantiopure, with the probability of a reliable assignment as greater than 90% for a three-hypothesis model (Hooft et al., 2008).

In order to confirm the absolute configuration, the data collection was repeated on the same crystal using an Oxford Diffraction Gemini A Ultra diffractometer and the Enhance Ultra (Cu Kα) source. For comparison, data were also collected on the same diffractometer using Mo Kα radiation and on a second Nonius KappaCCD diffractometer (Mo Kα). The Flack x parameter, the Hooft y parameter, G (all with s.u. values) and the probabilities derived from these values are given in Table 2.

In all four cases, the s.u. values are greater than the value of 0.10 suggested as the upper limit for confidently determining the absolute configuration of a known enantiopure compound (Flack & Bernardinelli, 2000). However, in order to achieve s.u. values of this magnitude with only carbon, hydrogen, nitrogen and oxygen present in the crystal, the data need to be of exceptional quality. Nonetheless, the likelihood that the absolute structure is incorrect given the data collected with Cu Kα radiation seems very small.

Examination of the three cases where data were collected with Mo Kα radiation is also interesting. In two of these three examples, the Flack x parameter was considerably outside the meaningful range for the parameter, and for all three, the s.u. was exceptionally large, indicating that the absolute configuration could not be determined. In contrast, examination of the Bijvoet pairs using the Hooft method suggests that the absolute configuration could be determined with a high confidence.

Related literature

For related literature, see: Oxford Diffraction (2008); Altomare et al. (1994); Asano et al. (2001); Betteridge et al. (2003); Choi et al. (1991); Cosier & Glazer (1986); Flack (1983); Flack & Bernardinelli (2000); Fleet et al. (1988); Harris et al. (1989); Hooft et al. (2008); Kato et al. (1999, 2003, 2007); Kumar & Pinto (2006); Molyneux et al. (1988); Nash et al. (1988, 1990); Otwinowski & Minor (1997); Takahashi et al. (2008); Tropea et al. (1989); Trost et al. (2007); Watson et al. (2001); Wormald et al. (1998).

S2. Experimental

The title compound was isolated from Castanospermum australe and crystallized from an ethanol/water/acetone mixture. The melting point was recorded as 432–434 K. [α]_D²⁵ +53.4 (c, 0.43 in H₂O).

S3. Refinement

A colourless single crystal was mounted in a nylon loop using perfluoropolyether oil and quench-cooled to 150 K in a stream of cold N₂ using an Oxford Cryosystems Cryostream unit (Cosier & Glazer, 1986). Diffraction data were initially measured using a Nonius KappaCCD diffractometer (graphite-monochromated Mo Kα radiation, λ = 0.71073 Å). Given that the compound was known to be enantiopure, examination of the systematic absences of the intensity data showed the space group to be C2.

The H atoms were all visible in a difference map and were refined with soft restraints on the bond lengths and angles, to regularize their geometry (C—H in the range 0.93–0.98 Å), and U_iso(H) in the range 1.2–1.5 times U_eq of the parent atom, after which the positions were refined with riding constraints.

The Flack x parameter was refined and the Bijvoet pairs examined to give the Hooft y parameter, G and the probabilities that the absolute configuration was correct as explained above (Hooft et al., 2008) (Table 2).

The crystal was then remounted on an Oxford Diffraction Gemini A Ultra at 100 K, where data were collected using both Mo Kα (λ = 0.71073 Å) and Cu Kα (λ = 1.54184 Å) radiation. The atomic coordinates from the initial structure determination were refined against the data as above. Data were similarly collected on a second Nonius KappaCCD diffractometer (graphite-monochromated Mo Kα radiation) and the model refined.

Computing details

Data collection: COLLECT (Nonius, 2001) for (I), (IV); CrysAlis CCD (Oxford Diffraction, 2008) for (II), (III). Cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997) for (I), (IV); CrysAlis RED (Oxford Diffraction, 2008) for (II), (III). Data reduction: DENZO/SCALEPACK (Otwinowski & Minor, 1997) for (I), (IV); CrysAlis RED (Oxford Diffraction, 2008) for (II), (III). For all compounds, program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).

Figures

	Fig. 1. The structure of 1-epialexine from the Gemini–Cu data, shown with displacment ellipsoids drawn at the 50% probability level.
	Fig. 2. The hydrogen bonding between the 1-epialexine molecule and the water of crystallization in (I), viewed down the unique axis showing the C2 symmetry. The O14···N4 distance is 2.737 (2) Å and O14···O9 is 2.719 (2) Å for the Gemini–Cu data. [Symmetry codes: (i) -x + 3/2, y - 1/2, -z + 1; (ii) -x + 1, y, -z + 1; (iii) x - 1/2, y - 1/2, z.] Only iii matches the codes in Table 1.
	Fig. 3. The layered structure of (I) (viewed down the a axis). The hydrogen-bonding interactions are shown as dotted lines.

(I) (1S,2R,3R,7S,7aS)-1,2,7-trihydroxy-3- (hydroxymethyl)pyrrolizidine hemihydrate

Crystal data

C8H15NO4·0.5H2O	F(000) = 428
Mr = 198.22	Dx = 1.511 Mg m^−3
Monoclinic, C2	Melting point = 432–434 K
Hall symbol: C 2y	Mo Kα radiation, λ = 0.71073 Å
a = 12.4594 (6) Å	Cell parameters from 1049 reflections
b = 7.3115 (4) Å	θ = 5–27°
c = 9.5878 (5) Å	µ = 0.12 mm^−1
β = 93.843 (2)°	T = 150 K
V = 871.45 (8) Å^3	Plate, clear_pale_colourless
Z = 4	0.25 × 0.21 × 0.07 mm

Data collection

Nonius KappaCCD diffractometer	1863 reflections with I > 2.0σ(I)
Graphite monochromator	Rint = 0.030
ω scans	θmax = 27.5°, θmin = 5.2°
Absorption correction: multi-scan (DENZO/SCALEPACK; Otwinowski & Minor, 1997)	h = −15→16
Tmin = 0.91, Tmax = 0.99	k = −9→9
5649 measured reflections	l = −12→12
1943 independent reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.030	Method = Modified Sheldrick w = 1/[σ^2(F^2) + ( 0.02P)^2 + 0.67P] , where P = (max(Fo^2,0) + 2Fc^2)/3
wR(F^2) = 0.071	(Δ/σ)max = 0.000386
S = 0.98	Δρmax = 0.19 e Å^−3
1943 reflections	Δρmin = −0.17 e Å^−3
126 parameters	Absolute structure: Flack (1983), 875 Friedel-pairs
3 restraints	Absolute structure parameter: −1.1 (9)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq
C1	0.70350 (10)	0.6233 (2)	0.30188 (13)	0.0152
C2	0.77631 (11)	0.4619 (2)	0.26855 (14)	0.0155
C3	0.88541 (11)	0.5238 (2)	0.33364 (15)	0.0161
N4	0.89097 (9)	0.71993 (19)	0.29594 (12)	0.0159
C5	0.94192 (11)	0.7658 (2)	0.16307 (15)	0.0196
C6	0.87964 (11)	0.9330 (2)	0.10902 (15)	0.0202
C7	0.76460 (11)	0.8758 (2)	0.13353 (14)	0.0166
C8	0.77615 (10)	0.7882 (2)	0.27942 (14)	0.0152
O9	0.67845 (7)	0.62022 (17)	0.44553 (10)	0.0182
O10	0.73896 (8)	0.28951 (17)	0.31327 (11)	0.0203
C11	0.98058 (12)	0.4057 (2)	0.29967 (16)	0.0211
O12	0.98233 (8)	0.35959 (18)	0.15607 (11)	0.0223
O13	0.68650 (8)	1.01839 (16)	0.12209 (10)	0.0197
O14	0.5	0.4236 (2)	0.5	0.0183
H11	0.6368	0.6296	0.2394	0.0164*
H21	0.7813	0.4540	0.1665	0.0188*
H31	0.8799	0.5206	0.4349	0.0187*
H51	1.0192	0.7901	0.1845	0.0226*
H52	0.9311	0.6649	0.0954	0.0232*
H61	0.9006	1.0450	0.1649	0.0237*
H62	0.8904	0.9563	0.0087	0.0248*
H71	0.7406	0.7836	0.0624	0.0183*
H81	0.7645	0.8790	0.3504	0.0189*
H111	1.0491	0.4678	0.3306	0.0238*
H112	0.9761	0.2913	0.3526	0.0256*
H131	0.7035	1.1000	0.1836	0.0297*
H101	0.7643	0.2717	0.3950	0.0318*
H141	0.4665	0.3535	0.4394	0.0281*
H91	0.6227	0.5537	0.4484	0.0311*
H121	1.0392	0.4006	0.1293	0.0374*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0145 (6)	0.0168 (7)	0.0142 (6)	0.0006 (6)	0.0015 (5)	0.0000 (5)
C2	0.0153 (6)	0.0146 (6)	0.0167 (6)	−0.0002 (5)	0.0016 (5)	0.0013 (5)
C3	0.0144 (6)	0.0176 (7)	0.0162 (6)	−0.0004 (5)	0.0002 (5)	0.0016 (5)
N4	0.0132 (5)	0.0168 (6)	0.0180 (6)	−0.0003 (4)	0.0018 (4)	0.0015 (5)
C5	0.0165 (6)	0.0213 (8)	0.0215 (7)	0.0002 (6)	0.0052 (5)	0.0035 (6)
C6	0.0182 (7)	0.0209 (7)	0.0219 (7)	−0.0007 (6)	0.0045 (5)	0.0032 (6)
C7	0.0164 (6)	0.0150 (7)	0.0182 (6)	0.0008 (5)	0.0012 (5)	−0.0001 (5)
C8	0.0136 (6)	0.0153 (7)	0.0167 (6)	0.0000 (5)	0.0010 (5)	−0.0013 (5)
O9	0.0174 (4)	0.0208 (5)	0.0167 (5)	−0.0038 (4)	0.0044 (4)	−0.0019 (4)
O10	0.0230 (5)	0.0159 (5)	0.0216 (5)	−0.0028 (4)	−0.0005 (4)	0.0017 (4)
C11	0.0172 (7)	0.0236 (8)	0.0225 (7)	0.0058 (6)	0.0012 (5)	0.0019 (6)
O12	0.0190 (5)	0.0249 (6)	0.0236 (5)	0.0007 (4)	0.0047 (4)	−0.0030 (5)
O13	0.0186 (5)	0.0183 (5)	0.0217 (5)	0.0038 (4)	−0.0007 (4)	0.0005 (4)
O14	0.0168 (7)	0.0191 (8)	0.0190 (7)	0.0000	0.0002 (5)	0.0000

Geometric parameters (Å, º)

C1—C2	1.5351 (19)	C6—H61	1.003
C1—C8	1.5317 (19)	C6—H62	0.994
C1—O9	1.4326 (15)	C7—C8	1.5362 (19)
C1—H11	0.993	C7—O13	1.4255 (17)
C2—C3	1.5260 (19)	C7—H71	0.991
C2—O10	1.4195 (18)	C8—H81	0.969
C2—H21	0.986	O9—H91	0.850
C3—N4	1.4815 (19)	O10—H101	0.835
C3—C11	1.520 (2)	C11—O12	1.4190 (18)
C3—H31	0.978	C11—H111	0.995
N4—C5	1.4990 (17)	C11—H112	0.982
N4—C8	1.5135 (17)	O12—H121	0.826
C5—C6	1.520 (2)	O13—H131	0.856
C5—H51	0.987	O14—H141^i	0.862
C5—H52	0.986	O14—H141	0.862
C6—C7	1.5265 (19)
C2—C1—C8	102.30 (10)	C5—C6—H61	111.4
C2—C1—O9	110.98 (11)	C7—C6—H61	110.8
C8—C1—O9	108.44 (11)	C5—C6—H62	111.6
C2—C1—H11	113.1	C7—C6—H62	112.6
C8—C1—H11	110.9	H61—C6—H62	109.2
O9—C1—H11	110.7	C6—C7—C8	102.87 (11)
C1—C2—C3	102.08 (11)	C6—C7—O13	115.52 (12)
C1—C2—O10	114.16 (11)	C8—C7—O13	113.38 (11)
C3—C2—O10	116.17 (11)	C6—C7—H71	108.9
C1—C2—H21	109.2	C8—C7—H71	110.4
C3—C2—H21	108.0	O13—C7—H71	105.8
O10—C2—H21	107.0	C7—C8—C1	115.85 (11)
C2—C3—N4	104.03 (11)	C7—C8—N4	105.25 (11)
C2—C3—C11	115.46 (12)	C1—C8—N4	106.80 (12)
N4—C3—C11	116.61 (12)	C7—C8—H81	110.2
C2—C3—H31	106.2	C1—C8—H81	108.8
N4—C3—H31	105.9	N4—C8—H81	109.8
C11—C3—H31	107.9	C1—O9—H91	105.7
C3—N4—C5	116.96 (11)	C2—O10—H101	108.1
C3—N4—C8	106.58 (11)	C3—C11—O12	113.94 (12)
C5—N4—C8	106.77 (11)	C3—C11—H111	110.1
N4—C5—C6	103.54 (11)	O12—C11—H111	109.2
N4—C5—H51	109.0	C3—C11—H112	107.5
C6—C5—H51	113.3	O12—C11—H112	107.7
N4—C5—H52	110.2	H111—C11—H112	108.2
C6—C5—H52	109.5	C11—O12—H121	106.5
H51—C5—H52	111.1	C7—O13—H131	108.7
C5—C6—C7	100.97 (11)	H141^i—O14—H141	107.0

Symmetry code: (i) −x+1, y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H52···O12	0.99	2.38	3.014 (2)	121
C6—H61···O12^ii	1.00	2.52	3.390 (2)	145
O13—H131···O10^ii	0.86	1.89	2.749 (2)	177
O10—H101···O9^iii	0.83	1.98	2.761 (2)	155
O14—H141···N4^iv	0.86	1.89	2.745 (2)	175
O9—H91···O14	0.85	1.89	2.727 (2)	166
O12—H121···O13^v	0.83	2.03	2.835 (2)	164

Symmetry codes: (ii) x, y+1, z; (iii) −x+3/2, y−1/2, −z+1; (iv) x−1/2, y−1/2, z; (v) x+1/2, y−1/2, z.

(II) (1S,2R,3R,7S,7aS)-1,2,7-trihydroxy-3- (hydroxymethyl)pyrrolizidine hemihydrate

Crystal data

C8H15NO4·0.5H2O	F(000) = 428
Mr = 198.22	Dx = 1.519 Mg m^−3
Monoclinic, C2	Melting point = 432–434 K
Hall symbol: C 2y	Mo Kα radiation, λ = 0.71073 Å
a = 12.4267 (3) Å	Cell parameters from 5964 reflections
b = 7.30208 (18) Å	θ = 5.2–31.5°
c = 9.5708 (2) Å	µ = 0.12 mm^−1
β = 93.839 (2)°	T = 100 K
V = 866.51 (4) Å^3	Plate, clear_pale_colourless
Z = 4	0.25 × 0.21 × 0.07 mm

Data collection

Oxford Diffraction Gemini A Ultra CCD diffractometer	1724 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1402 reflections with I > 2.0σ(I)
Graphite monochromator	Rint = 0.030
ω scans	θmax = 25.1°, θmin = 3.8°
Absorption correction: multi-scan [empirical (using intensity measurements) absorption correction using spherical harmonics (CrysAlis RED) implementing the SCALE3 ABSPACK scaling algorithm (Oxford Diffraction, 2008)]	h = −15→14
Tmin = 0.92, Tmax = 0.99	k = −9→9
7771 measured reflections	l = −11→11

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.026	Method = Modified Sheldrick w = 1/[σ^2(F^2) + ( 0.04P)^2 + 0.0P] , where P = (max(Fo^2,0) + 2Fc^2)/3
wR(F^2) = 0.064	(Δ/σ)max = 0.001
S = 1.01	Δρmax = 0.19 e Å^−3
1511 reflections	Δρmin = −0.16 e Å^−3
126 parameters	Absolute structure: Flack (1983), 777 Friedel-pairs
3 restraints	Absolute structure parameter: −1.5 (9)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq
C1	0.70347 (12)	0.6234 (2)	0.30227 (16)	0.0111
C2	0.77593 (12)	0.4618 (2)	0.26825 (16)	0.0111
C3	0.88550 (12)	0.5236 (2)	0.33368 (17)	0.0120
N4	0.89097 (11)	0.7201 (2)	0.29592 (14)	0.0119
C5	0.94194 (12)	0.7657 (2)	0.16284 (17)	0.0141
C6	0.87980 (13)	0.9327 (2)	0.10843 (18)	0.0149
C7	0.76468 (14)	0.8763 (2)	0.13319 (17)	0.0126
C8	0.77599 (13)	0.7884 (2)	0.27916 (17)	0.0115
O9	0.67852 (8)	0.62057 (18)	0.44568 (11)	0.0134
O10	0.73856 (9)	0.28941 (18)	0.31306 (12)	0.0148
C11	0.98061 (14)	0.4056 (2)	0.29969 (18)	0.0152
O12	0.98239 (9)	0.35930 (18)	0.15566 (12)	0.0164
O13	0.68619 (8)	1.01858 (18)	0.12166 (12)	0.0144
O14	0.500000 (10)	0.4232 (2)	0.500000 (10)	0.0137
H11	0.6384	0.6260	0.2407	0.0094*
H21	0.7801	0.4512	0.1681	0.0110*
H31	0.8812	0.5192	0.4349	0.0119*
H51	1.0180	0.7885	0.1822	0.0157*
H52	0.9313	0.6686	0.0944	0.0157*
H61	0.9002	1.0416	0.1630	0.0163*
H62	0.8912	0.9533	0.0090	0.0180*
H71	0.7411	0.7848	0.0641	0.0130*
H81	0.7660	0.8788	0.3513	0.0136*
H111	1.0477	0.4640	0.3323	0.0169*
H112	0.9777	0.2905	0.3535	0.0182*
H131	0.7031	1.0980	0.1823	0.0208*
H101	0.7667	0.2682	0.3883	0.0235*
H141	0.4680	0.3528	0.4410	0.0210*
H91	0.6257	0.5544	0.4497	0.0204*
H121	1.0364	0.3937	0.1290	0.0259*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0087 (7)	0.0139 (8)	0.0107 (8)	0.0005 (8)	0.0003 (6)	−0.0002 (7)
C2	0.0093 (8)	0.0124 (8)	0.0119 (8)	0.0019 (6)	0.0023 (6)	0.0010 (7)
C3	0.0117 (8)	0.0135 (8)	0.0107 (8)	−0.0017 (7)	0.0005 (6)	0.0006 (7)
N4	0.0098 (6)	0.0127 (7)	0.0136 (8)	−0.0003 (6)	0.0028 (5)	0.0012 (6)
C5	0.0116 (8)	0.0155 (9)	0.0157 (9)	−0.0010 (7)	0.0043 (6)	0.0011 (7)
C6	0.0147 (9)	0.0141 (8)	0.0160 (8)	−0.0016 (8)	0.0029 (7)	0.0013 (7)
C7	0.0138 (8)	0.0097 (8)	0.0144 (8)	0.0009 (6)	0.0014 (6)	−0.0016 (7)
C8	0.0104 (8)	0.0116 (8)	0.0126 (8)	0.0007 (7)	0.0006 (6)	−0.0022 (7)
O9	0.0113 (5)	0.0158 (6)	0.0134 (6)	−0.0039 (5)	0.0044 (4)	−0.0016 (5)
O10	0.0159 (6)	0.0121 (6)	0.0160 (6)	−0.0021 (5)	−0.0011 (4)	0.0017 (5)
C11	0.0125 (8)	0.0154 (10)	0.0174 (9)	0.0027 (7)	−0.0004 (6)	0.0017 (7)
O12	0.0123 (6)	0.0182 (6)	0.0191 (7)	−0.0005 (5)	0.0040 (4)	−0.0023 (5)
O13	0.0135 (6)	0.0126 (6)	0.0170 (6)	0.0023 (5)	−0.0002 (4)	−0.0001 (5)
O14	0.0110 (8)	0.0153 (9)	0.0146 (9)	0.0000	0.0003 (6)	0.0000

Geometric parameters (Å, º)

C1—C2	1.533 (2)	C6—H61	0.976
C1—C8	1.529 (2)	C6—H62	0.983
C1—O9	1.4274 (18)	C7—C8	1.536 (2)
C1—H11	0.968	C7—O13	1.4241 (19)
C2—C3	1.528 (2)	C7—H71	0.971
C2—O10	1.418 (2)	C8—H81	0.970
C2—H21	0.966	O9—H91	0.818
C3—N4	1.482 (2)	O10—H101	0.795
C3—C11	1.515 (2)	C11—O12	1.421 (2)
C3—H31	0.974	C11—H111	0.969
N4—C5	1.497 (2)	C11—H112	0.987
N4—C8	1.512 (2)	O12—H121	0.775
C5—C6	1.517 (2)	O13—H131	0.837
C5—H51	0.965	O14—H141^i	0.844
C5—H52	0.968	O14—H141	0.844
C6—C7	1.522 (2)
C2—C1—C8	102.44 (12)	C5—C6—H61	111.3
C2—C1—O9	111.19 (13)	C7—C6—H61	110.5
C8—C1—O9	108.59 (12)	C5—C6—H62	110.6
C2—C1—H11	111.4	C7—C6—H62	112.9
C8—C1—H11	111.9	H61—C6—H62	110.2
O9—C1—H11	111.0	C6—C7—C8	103.00 (13)
C1—C2—C3	101.86 (12)	C6—C7—O13	115.89 (13)
C1—C2—O10	114.23 (13)	C8—C7—O13	113.34 (14)
C3—C2—O10	116.03 (13)	C6—C7—H71	108.9
C1—C2—H21	110.1	C8—C7—H71	109.7
C3—C2—H21	108.9	O13—C7—H71	106.0
O10—C2—H21	105.6	C7—C8—C1	116.24 (12)
C2—C3—N4	103.88 (12)	C7—C8—N4	105.24 (13)
C2—C3—C11	115.50 (14)	C1—C8—N4	106.68 (13)
N4—C3—C11	116.67 (14)	C7—C8—H81	110.8
C2—C3—H31	106.9	C1—C8—H81	109.2
N4—C3—H31	106.3	N4—C8—H81	108.3
C11—C3—H31	106.9	C1—O9—H91	106.3
C3—N4—C5	116.84 (13)	C2—O10—H101	108.3
C3—N4—C8	106.66 (13)	C3—C11—O12	113.99 (13)
C5—N4—C8	106.68 (12)	C3—C11—H111	110.3
N4—C5—C6	103.66 (13)	O12—C11—H111	110.4
N4—C5—H51	109.9	C3—C11—H112	108.4
C6—C5—H51	113.3	O12—C11—H112	107.9
N4—C5—H52	111.5	H111—C11—H112	105.5
C6—C5—H52	108.3	C11—O12—H121	108.2
H51—C5—H52	110.1	C7—O13—H131	108.2
C5—C6—C7	101.02 (13)	H141^i—O14—H141	104.9

Symmetry code: (i) −x+1, y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H52···O12	0.97	2.41	3.011 (2)	120
C6—H61···O12^ii	0.98	2.54	3.384 (2)	145
O13—H131···O10^ii	0.84	1.91	2.744 (2)	177
O10—H101···O9^iii	0.79	2.00	2.756 (2)	158
O14—H141···N4^iv	0.84	1.90	2.738 (2)	173
O9—H91···O14	0.82	1.92	2.724 (2)	167
O12—H121···O13^v	0.78	2.08	2.825 (2)	162

Symmetry codes: (ii) x, y+1, z; (iii) −x+3/2, y−1/2, −z+1; (iv) x−1/2, y−1/2, z; (v) x+1/2, y−1/2, z.

(III) (1S,2R,3R,7S,7aS)-1,2,7-trihydroxy-3- (hydroxymethyl)pyrrolizidine hemihydrate

Crystal data

C8H15NO4·0.5H2O	F(000) = 428
Mr = 198.22	Dx = 1.523 Mg m^−3
Monoclinic, C2	Melting point = 432–434 K
Hall symbol: C 2y	Cu Kα radiation, λ = 1.54184 Å
a = 12.4190 (4) Å	Cell parameters from 2205 reflections
b = 7.2933 (2) Å	θ = 4.6–66.8°
c = 9.5671 (3) Å	µ = 1.05 mm^−1
β = 93.841 (3)°	T = 100 K
V = 864.60 (5) Å^3	Plate, clear_pale_colourless
Z = 4	0.25 × 0.21 × 0.07 mm

Data collection

Oxford Diffraction Gemini A Ultra CCD diffractometer	1479 independent reflections
Radiation source: Enhance Ultra (Cu) X-ray Source	1464 reflections with I > 2.0σ(I)
Multi-layer focusing mirror monochromator	Rint = 0.025
ω scans	θmax = 67.1°, θmin = 7.2°
Absorption correction: multi-scan [empirical (using intensity measurements) absorption correction using spherical harmonics (CrysAlis RED) implementing the SCALE3 ABSPACK scaling algorithm (Oxford Diffraction, 2008)]	h = −14→14
Tmin = 0.80, Tmax = 0.92	k = −8→8
7817 measured reflections	l = −11→11

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.026	Method = Modified Sheldrick w = 1/[σ^2(F^2) + ( 0.05P)^2 + 0.45P] , where P = (max(Fo^2,0) + 2Fc^2)/3
wR(F^2) = 0.071	(Δ/σ)max = 0.001
S = 1.06	Δρmax = 0.19 e Å^−3
1476 reflections	Δρmin = −0.15 e Å^−3
126 parameters	Absolute structure: Flack (1983), 650 Friedel-pairs
3 restraints	Absolute structure parameter: −0.01 (17)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq
C1	0.70337 (11)	0.6235 (2)	0.30236 (14)	0.0138
C2	0.77569 (11)	0.4617 (2)	0.26825 (14)	0.0132
C3	0.88551 (11)	0.5236 (2)	0.33385 (15)	0.0143
N4	0.89103 (10)	0.71996 (19)	0.29579 (13)	0.0138
C5	0.94218 (11)	0.7659 (2)	0.16282 (15)	0.0160
C6	0.87956 (12)	0.9330 (2)	0.10817 (16)	0.0169
C7	0.76429 (12)	0.8761 (2)	0.13328 (16)	0.0146
C8	0.77603 (11)	0.7881 (2)	0.27924 (15)	0.0139
O9	0.67830 (8)	0.62039 (17)	0.44567 (10)	0.0156
O10	0.73843 (8)	0.28957 (17)	0.31297 (11)	0.0165
C11	0.98073 (13)	0.4055 (2)	0.29938 (17)	0.0175
O12	0.98231 (8)	0.35919 (18)	0.15575 (11)	0.0181
O13	0.68616 (8)	1.01883 (16)	0.12185 (10)	0.0163
O14	0.500000 (10)	0.4233 (2)	0.500000 (10)	0.0149
H11	0.6387	0.6261	0.2403	0.0163*
H21	0.7797	0.4532	0.1687	0.0142*
H31	0.8809	0.5188	0.4329	0.0148*
H51	1.0178	0.7911	0.1829	0.0185*
H52	0.9320	0.6684	0.0949	0.0180*
H61	0.9002	1.0404	0.1628	0.0192*
H62	0.8898	0.9552	0.0097	0.0189*
H71	0.7403	0.7840	0.0645	0.0159*
H81	0.7659	0.8768	0.3494	0.0162*
H111	1.0461	0.4680	0.3295	0.0193*
H112	0.9784	0.2911	0.3505	0.0204*
H131	0.7010	1.0999	0.1826	0.0233*
H101	0.7632	0.2678	0.3897	0.0254*
H141	0.4713	0.3529	0.4398	0.0226*
H91	0.6279	0.5513	0.4471	0.0237*
H121	1.0345	0.4030	0.1262	0.0278*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0140 (6)	0.0146 (7)	0.0130 (7)	−0.0002 (6)	0.0016 (5)	−0.0003 (6)
C2	0.0113 (7)	0.0140 (7)	0.0145 (7)	0.0000 (5)	0.0014 (5)	0.0012 (5)
C3	0.0133 (7)	0.0167 (7)	0.0127 (6)	−0.0023 (6)	0.0009 (5)	0.0006 (6)
N4	0.0114 (6)	0.0139 (6)	0.0163 (6)	0.0000 (5)	0.0024 (4)	0.0004 (5)
C5	0.0142 (7)	0.0158 (7)	0.0185 (8)	−0.0007 (6)	0.0041 (6)	0.0016 (6)
C6	0.0157 (7)	0.0162 (7)	0.0190 (7)	−0.0016 (6)	0.0038 (6)	0.0011 (6)
C7	0.0139 (7)	0.0120 (7)	0.0181 (7)	−0.0003 (5)	0.0023 (5)	−0.0013 (6)
C8	0.0109 (7)	0.0138 (7)	0.0168 (7)	0.0006 (5)	0.0008 (5)	−0.0029 (6)
O9	0.0134 (4)	0.0167 (5)	0.0171 (5)	−0.0033 (4)	0.0044 (4)	−0.0015 (4)
O10	0.0181 (5)	0.0136 (5)	0.0176 (5)	−0.0019 (4)	−0.0002 (4)	0.0009 (4)
C11	0.0133 (7)	0.0182 (8)	0.0208 (7)	0.0033 (6)	−0.0006 (5)	0.0023 (6)
O12	0.0145 (5)	0.0195 (5)	0.0209 (6)	0.0003 (4)	0.0041 (4)	−0.0018 (4)
O13	0.0146 (5)	0.0150 (5)	0.0190 (5)	0.0024 (4)	−0.0002 (4)	−0.0002 (4)
O14	0.0130 (7)	0.0156 (7)	0.0158 (7)	0.0000	0.0002 (5)	0.0000

Geometric parameters (Å, º)

C1—C2	1.531 (2)	C6—H61	0.966
C1—C8	1.527 (2)	C6—H62	0.972
C1—O9	1.4263 (17)	C7—C8	1.535 (2)
C1—H11	0.967	C7—O13	1.4224 (18)
C2—C3	1.5307 (19)	C7—H71	0.972
C2—O10	1.4143 (19)	C8—H81	0.947
C2—H21	0.959	O9—H91	0.804
C3—N4	1.480 (2)	O10—H101	0.792
C3—C11	1.517 (2)	C11—O12	1.4166 (19)
C3—H31	0.954	C11—H111	0.958
N4—C5	1.4974 (18)	C11—H112	0.969
N4—C8	1.5104 (18)	O12—H121	0.792
C5—C6	1.520 (2)	O13—H131	0.841
C5—H51	0.963	O14—H141^i	0.834
C5—H52	0.965	O14—H141	0.834
C6—C7	1.525 (2)
C2—C1—C8	102.37 (11)	C5—C6—H61	110.7
C2—C1—O9	111.21 (12)	C7—C6—H61	110.7
C8—C1—O9	108.70 (11)	C5—C6—H62	111.7
C2—C1—H11	111.1	C7—C6—H62	112.5
C8—C1—H11	111.8	H61—C6—H62	110.0
O9—C1—H11	111.4	C6—C7—C8	102.96 (12)
C1—C2—C3	101.81 (12)	C6—C7—O13	115.55 (12)
C1—C2—O10	114.27 (11)	C8—C7—O13	113.49 (12)
C3—C2—O10	116.00 (12)	C6—C7—H71	109.2
C1—C2—H21	109.4	C8—C7—H71	109.4
C3—C2—H21	108.8	O13—C7—H71	106.1
O10—C2—H21	106.4	C7—C8—C1	116.07 (11)
C2—C3—N4	103.83 (12)	C7—C8—N4	105.33 (11)
C2—C3—C11	115.44 (12)	C1—C8—N4	106.85 (12)
N4—C3—C11	116.49 (12)	C7—C8—H81	110.5
C2—C3—H31	106.6	C1—C8—H81	109.1
N4—C3—H31	106.7	N4—C8—H81	108.7
C11—C3—H31	107.2	C1—O9—H91	104.3
C3—N4—C5	117.03 (11)	C2—O10—H101	110.1
C3—N4—C8	106.56 (12)	C3—C11—O12	114.08 (12)
C5—N4—C8	106.82 (11)	C3—C11—H111	108.8
N4—C5—C6	103.60 (11)	O12—C11—H111	109.8
N4—C5—H51	109.7	C3—C11—H112	109.2
C6—C5—H51	112.6	O12—C11—H112	106.7
N4—C5—H52	111.3	H111—C11—H112	108.1
C6—C5—H52	108.5	C11—O12—H121	108.3
H51—C5—H52	110.9	C7—O13—H131	110.2
C5—C6—C7	101.04 (12)	H141^i—O14—H141	104.1

Symmetry code: (i) −x+1, y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H52···O12	0.97	2.40	3.009 (2)	121
C6—H61···O12^ii	0.97	2.54	3.379 (2)	145
O13—H131···O10^ii	0.84	1.90	2.739 (2)	177
O10—H101···O9^iii	0.79	2.00	2.758 (2)	159
O14—H141···N4^iv	0.83	1.91	2.737 (2)	172
O9—H91···O14	0.80	1.94	2.719 (2)	163
O12—H121···O13^v	0.79	2.07	2.825 (2)	160

Symmetry codes: (ii) x, y+1, z; (iii) −x+3/2, y−1/2, −z+1; (iv) x−1/2, y−1/2, z; (v) x+1/2, y−1/2, z.

(IV) (1S,2R,3R,7S,7aS)-1,2,7-trihydroxy-3- (hydroxymethyl)pyrrolizidine hemihydrate

Crystal data

C8H15NO4·0.5H2O	F(000) = 428
Mr = 198.22	Dx = 1.511 Mg m^−3
Monoclinic, C2	Melting point = 432–434 K
Hall symbol: C 2y	Mo Kα radiation, λ = 0.71073 Å
a = 12.4567 (5) Å	Cell parameters from 1058 reflections
b = 7.3097 (3) Å	θ = 5–27°
c = 9.5920 (5) Å	µ = 0.12 mm^−1
β = 93.8151 (16)°	T = 150 K
V = 871.46 (7) Å^3	Plate, clear_pale_colourless
Z = 4	0.25 × 0.21 × 0.07 mm

Data collection

Nonius KappaCCD diffractometer	1862 reflections with I > 2.0σ(I)
Graphite monochromator	Rint = 0.032
ω scans	θmax = 27.5°, θmin = 5.2°
Absorption correction: multi-scan (DENZO/SCALEPACK; Otwinowski & Minor, 1997)	h = −15→16
Tmin = 0.94, Tmax = 0.99	k = −9→9
7632 measured reflections	l = −12→12
1974 independent reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.029	Method = Modified Sheldrick w = 1/[σ^2(F^2) + ( 0.03P)^2 + 0.49P] , where P = (max(Fo^2,0) + 2Fc^2)/3
wR(F^2) = 0.067	(Δ/σ)max = 0.001
S = 1.01	Δρmax = 0.34 e Å^−3
1974 reflections	Δρmin = −0.33 e Å^−3
126 parameters	Absolute structure: Flack (1983), 0 Friedel-pairs
3 restraints	Absolute structure parameter: −0.1 (8)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq
C1	0.70361 (10)	0.6232 (2)	0.30195 (13)	0.0137
C2	0.77609 (10)	0.4619 (2)	0.26861 (14)	0.0143
C3	0.88547 (10)	0.5239 (2)	0.33370 (14)	0.0146
N4	0.89109 (9)	0.72019 (18)	0.29614 (12)	0.0146
C5	0.94209 (10)	0.7657 (2)	0.16317 (14)	0.0180
C6	0.87957 (11)	0.9327 (2)	0.10874 (15)	0.0185
C7	0.76453 (11)	0.8757 (2)	0.13346 (14)	0.0154
C8	0.77615 (10)	0.7878 (2)	0.27932 (13)	0.0137
O9	0.67853 (7)	0.62031 (16)	0.44550 (9)	0.0167
O10	0.73887 (8)	0.28959 (16)	0.31313 (10)	0.0186
C11	0.98078 (12)	0.4060 (2)	0.29970 (15)	0.0195
O12	0.98235 (8)	0.35952 (17)	0.15619 (11)	0.0210
O13	0.68650 (7)	1.01845 (16)	0.12222 (10)	0.0181
O14	0.500000 (10)	0.4236 (2)	0.500000 (10)	0.0167
H11	0.6379	0.6274	0.2389	0.0144*
H21	0.7807	0.4538	0.1669	0.0171*
H31	0.8803	0.5196	0.4364	0.0161*
H51	1.0189	0.7889	0.1845	0.0219*
H52	0.9322	0.6657	0.0971	0.0218*
H61	0.8997	1.0448	0.1628	0.0207*
H62	0.8909	0.9554	0.0089	0.0227*
H71	0.7404	0.7833	0.0634	0.0161*
H81	0.7652	0.8784	0.3497	0.0163*
H111	1.0495	0.4687	0.3317	0.0227*
H112	0.9767	0.2906	0.3517	0.0232*
H131	0.7042	1.0989	0.1845	0.0272*
H101	0.7667	0.2697	0.3906	0.0293*
H141	0.4657	0.3548	0.4402	0.0256*
H91	0.6253	0.5497	0.4512	0.0284*
H121	1.0374	0.4014	0.1299	0.0347*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0130 (5)	0.0148 (6)	0.0133 (6)	0.0008 (6)	0.0014 (4)	0.0000 (5)
C2	0.0138 (6)	0.0130 (6)	0.0161 (6)	−0.0001 (5)	0.0013 (5)	0.0012 (5)
C3	0.0126 (6)	0.0153 (6)	0.0159 (6)	−0.0005 (5)	0.0004 (5)	0.0013 (5)
N4	0.0116 (5)	0.0151 (6)	0.0172 (6)	−0.0009 (4)	0.0020 (4)	0.0014 (4)
C5	0.0158 (6)	0.0186 (7)	0.0202 (7)	0.0005 (5)	0.0050 (5)	0.0031 (6)
C6	0.0167 (7)	0.0176 (7)	0.0214 (7)	−0.0010 (6)	0.0035 (5)	0.0031 (5)
C7	0.0150 (6)	0.0136 (6)	0.0177 (6)	0.0001 (5)	0.0015 (5)	−0.0005 (5)
C8	0.0122 (6)	0.0134 (6)	0.0153 (6)	−0.0004 (5)	0.0002 (5)	−0.0011 (5)
O9	0.0158 (4)	0.0194 (5)	0.0154 (5)	−0.0045 (4)	0.0045 (3)	−0.0018 (4)
O10	0.0207 (5)	0.0137 (5)	0.0209 (5)	−0.0029 (4)	−0.0018 (4)	0.0012 (4)
C11	0.0153 (6)	0.0211 (8)	0.0218 (7)	0.0057 (5)	0.0002 (5)	0.0018 (5)
O12	0.0170 (5)	0.0233 (5)	0.0232 (5)	0.0008 (4)	0.0044 (4)	−0.0028 (4)
O13	0.0168 (5)	0.0161 (5)	0.0210 (5)	0.0040 (4)	−0.0012 (4)	0.0005 (4)
O14	0.0146 (6)	0.0166 (7)	0.0187 (7)	0.0000	−0.0009 (5)	0.0000

Geometric parameters (Å, º)

C1—C2	1.5314 (18)	C6—H61	0.993
C1—C8	1.5291 (18)	C6—H62	0.992
C1—O9	1.4322 (15)	C7—C8	1.5373 (18)
C1—H11	0.985	C7—O13	1.4254 (16)
C2—C3	1.5290 (18)	C7—H71	0.986
C2—O10	1.4180 (17)	C8—H81	0.962
C2—H21	0.983	O9—H91	0.845
C3—N4	1.4824 (17)	O10—H101	0.811
C3—C11	1.5196 (19)	C11—O12	1.4194 (17)
C3—H31	0.992	C11—H111	1.001
N4—C5	1.4996 (16)	C11—H112	0.983
N4—C8	1.5131 (17)	O12—H121	0.807
C5—C6	1.5215 (19)	O13—H131	0.856
C5—H51	0.980	O14—H141^i	0.856
C5—H52	0.970	O14—H141	0.856
C6—C7	1.5260 (19)
C2—C1—C8	102.35 (10)	C5—C6—H61	112.1
C2—C1—O9	111.02 (11)	C7—C6—H61	110.6
C8—C1—O9	108.47 (10)	C5—C6—H62	111.3
C2—C1—H11	111.9	C7—C6—H62	113.0
C8—C1—H11	111.3	H61—C6—H62	108.6
O9—C1—H11	111.4	C6—C7—C8	102.88 (11)
C1—C2—C3	102.04 (10)	C6—C7—O13	115.53 (11)
C1—C2—O10	114.32 (10)	C8—C7—O13	113.40 (11)
C3—C2—O10	116.13 (11)	C6—C7—H71	109.2
C1—C2—H21	109.2	C8—C7—H71	109.9
C3—C2—H21	108.3	O13—C7—H71	105.9
O10—C2—H21	106.7	C7—C8—C1	115.92 (10)
C2—C3—N4	104.04 (11)	C7—C8—N4	105.35 (10)
C2—C3—C11	115.61 (11)	C1—C8—N4	106.95 (11)
N4—C3—C11	116.51 (11)	C7—C8—H81	110.0
C2—C3—H31	106.3	C1—C8—H81	109.2
N4—C3—H31	106.2	N4—C8—H81	109.1
C11—C3—H31	107.4	C1—O9—H91	107.1
C3—N4—C5	116.80 (11)	C2—O10—H101	107.9
C3—N4—C8	106.42 (10)	C3—C11—O12	113.91 (11)
C5—N4—C8	106.75 (10)	C3—C11—H111	109.8
N4—C5—C6	103.51 (10)	O12—C11—H111	109.9
N4—C5—H51	108.9	C3—C11—H112	108.0
C6—C5—H51	113.8	O12—C11—H112	106.9
N4—C5—H52	110.2	H111—C11—H112	108.0
C6—C5—H52	109.9	C11—O12—H121	106.2
H51—C5—H52	110.3	C7—O13—H131	107.9
C5—C6—C7	101.08 (11)	H141^i—O14—H141	108.1

Symmetry code: (i) −x+1, y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H52···O12	0.97	2.38	3.012 (2)	122
C6—H61···O12^ii	0.99	2.52	3.392 (2)	146
O13—H131···O10^ii	0.86	1.89	2.747 (2)	176
O10—H101···O9^iii	0.81	2.00	2.763 (2)	157
O14—H141···N4^iv	0.86	1.89	2.743 (2)	175
O9—H91···O14	0.84	1.90	2.728 (2)	167
O12—H121···O13^v	0.81	2.05	2.834 (2)	164

Symmetry codes: (ii) x, y+1, z; (iii) −x+3/2, y−1/2, −z+1; (iv) x−1/2, y−1/2, z; (v) x+1/2, y−1/2, z.