research communications
of memantine–carboxyborane
aDepartment of Chemistry, University of Alaska Anchorage, Anchorage, AK 99508, USA, and bDepartment of Chemistry, University of California–San Diego, La Jolla, CA 92093, USA
*Correspondence e-mail: ndingra@alaska.edu
The synthesis and 13H24BNO2 [systematic name: 3,5-dimethyladamantanylamine–boranecarboxylic acid or N-(carboxyboranylidene)-3,5-dimethyladamantan-1-amine], derived from the anti-Alzheimer's disease drug memantine is reported. The C—N—B—CO2 unit is almost planar (r.m.s. deviation = 0.095 Å). The extended structure shows typical carboxylic acid inversion dimers linked by pairwise O—H⋯O hydrogen bonds [O⋯O = 2.662 (3) Å]. The amino group forms a weak N—H⋯O hydrogen bond [N⋯O = 3.011 (3) Å], linking the dimers into [001] chains in the crystal. Highly disordered solvent molecules were treated using the SQUEEZE routine of PLATON [Spek (2015). Acta Cryst. C71, 9–18], which treats the electron density as a diffuse contribution without assignment of specific atom locations. A scattering contribution of 255 electrons was removed. The crystal studied was refined as a two-component twin.
of the title compound, CKeywords: crystal structure; memantine-carboxyborane; CORCB; memantine; adamantane.
CCDC reference: 1905840
1. Chemical context
Memantine is a drug used for the treatment of mild and moderate-to-severe Alzheimer's disease as an inhibitor for N-methyl-D-aspartate (NMDA) receptors. As a result of its property as a low-affinity, open-channel blocker, memantine does not substantially interfere with normal synaptic activity, thereby reducing side effects. This has led to clinical trials for other neurological disorders (Bullock, 2006; Lipton, 2005; Olivares et al., 2012; Parsons et al., 2007). While memantine in its hydrochloride form is useful in various treatment methods, some modifications were done on this drug to optimize the desired concentration in the system. As a means to preventing drug degradation, memantine has been further processed in a mixture with other compounds (McInnes et al., 2010; Plosker, 2015). The one-week extended release formula by Lyndra Therapeutics is currently under clinical trial phase I (clinicaltrials.gov, NCT03711825). Though efforts to maintain the long-term stability of memantine are underway, chemical modification of the memantine structure itself is rarely reported. Our attempt was to mask the compound with an additional moiety that can be removed under certain conditions, therefore releasing the drug. With this goal, memantine–carboxyborane was synthesized since the carboxyborate group is known to decompose into carbon monoxide and boric acid, leaving the drug molecule itself (Ayudhya et al., 2017, 2018). The single of the said compound, (I), was solved and its features are described in this report.
2. Structural commentary
The molecular structure of (I) is shown in Fig. 1. The C2–N1–B1–C1/O1/O2 fragment is almost planar (r.m.s. deviation = 0.095 Å) and the C atoms bonded to the B and N atoms take on an anti orientation [C1—B1—N1—C2 = 173.5 (3)°]. The stereogenic centres in the adamantane unit were assigned as C4 S and C8 R in the arbitrarily chosen but crystal symmetry generates a The bond lengths [C1—O1 = 1.340 (4), C1—O2 = 1.227 (4) Å] of the carboxylic acid group are in agreement with the data for related carboxylic acids and known amine–carboxyboranes (Gavezzotti, 2008; Spielvogel et al., 1980; Vyakaranam et al., 2002; Ayudhya et al., 2017). The C—C—C bond angles of the adamantine cage fall within the expected ranges and the N1—C2 bond length at 1.504 (4) Å is comparable with previously reported values in aminoadamantane structures (Donohue & Goodman, 1967; Chacko & Zand, 1973).
3. Supramolecular features
A dimer is observed between the two memantine–carboxyborane molecules formed through conventional hydrogen bonding between the carboxylic acid moieties (Fig. 2). The hydrogen-bond length listed in Table 1 [O1⋯O2 = 2.662 (3) Å] is consistent with the hydrogen-bond geometries found in carboxyborane dimers such as ammonia–carboxyborane [2.668 (2) Å; Spielvogel et al., 1980], mophorline–carboxyborane [2.712 (4) Å; Vyakaranam et al., 2002] and trimethylamine–carboxyborane [2.714 Å; Spielvogel et al., 1976]. In (I), these dimers form an extended structure through N1—H1B⋯O1 links (O1 is the protonated oxygen atom of the carboxylic acid), to form [001] chains. This motif has also been reported previously in ammonia–carboxyborane, trimethylamine–carboxyborane, dimethylamine–carboxyborane and methylamine–carboxyborane (Spielvogel et al., 1980). The adjacent dimers shown in Fig. 2 indicates that the planes of the carboxylic acids are not parallel, but twisted by 76.5° from each other.
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Assessment of available crystal structures deposited with the Cambridge Structural Database (Version 5.39; Groom et al., 2016) indicates that not all amine–carboxyboranes form dimers during crystallization. While some amine–carboxyboranes described above are dimers, others such as piperidine–carboxyborane and hexamethylenetetramine–carboxyborane do not form dimers, suggesting that the amine-group interaction may influence the overall packing (Rana et al., 2002; Ayudhya et al., 2017). The extended structure of (I) is shown in projection down the b- and c-axis directions in Fig. 3a and 3b, respectively. No other contacts beyond the hydrogen bonds already mentioned are observed in this packing. Although the dimers appear to be parallel in Fig. 3a, the twisted planes of hydrogen bonds are better represented in Fig. 3b.
4. Database survey
The memantine structure in its free (unprotonated) base form is not found in the literature, although the hydrochloride salt with water molecules of crystallization has been solved (Lou et al., 2009). Another memantine reported was in a clathrate form with cucurbit[7]uril where memantine is completely bound within the cavity (McInnes et al., 2010). However, numerous crystal structures of the adamantane cage and its derivatives in various forms have been reported over many years (Nordman & Schmitkons, 1965; Chacko & Zand, 1973; SiMa, 2009; Glaser et al., 2011).
5. Synthesis and crystallization
Memantine, a derivative of adamantine, was first synthesized by Eli Lilly and Company. In an attempt to modify memantine into memantine–carboxyborane, a reaction scheme as shown in Fig. 4 was carried out. Addition of the carboxyborane moiety to memantine was done in a one-step reaction using an amine-exchange process as previously described (Spielvogel et al., 1980). Trimethylamine carboxyborane (117 mg, 1.0 mmol) and memantine (780 mg, 4.4 mmol) were dissolved in tetrahydrofuran (8.0 ml), and maintained at 328 K for 24 h under a nitrogen atmosphere. The solution was concentrated by vacuum distillation and the resulting solid was dissolved in dichloromethane. The product was precipitated from the solvent by using 15 ml of hexane and the white solid crude product (208 mg) was filtered. This residue was purified by multiple recrystallization in dichloromethane/hexane to yield a white solid (15 mg, 6.3%). Crystals suitable for X-ray analysis were prepared by dissolving in toluene and slow cooling of the solution.
6. Refinement
Crystal data collection and structure . H atoms were placed in calculated positions (O—H = 0.84, N—H = 0.91 and C—H = 0.98–0.99 Å) and refined as riding with Uiso(eq) = 1.5Ueq(C-methyl, O) and 1.2Ueq(C, N) for all others. The idealized methyl groups at C12 and C13 and the idealized tetrahedral OH group at O1 were refined as rotating groups. The disordered solvent molecules were treated with the SQUEEZE routine in PLATON (Spek, 2015). The crystal studied was refined as a two-component twin.
details are summarized in Table 2Supporting information
CCDC reference: 1905840
https://doi.org/10.1107/S2056989019004092/hb7806sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019004092/hb7806Isup2.hkl
Graphical Abstract. DOI: https://doi.org/10.1107/S2056989019004092/hb7806sup3.tif
Supporting information file. DOI: https://doi.org/10.1107/S2056989019004092/hb7806Isup4.cdx
Supporting information file. DOI: https://doi.org/10.1107/S2056989019004092/hb7806Isup5.cdx
Supporting information file. DOI: https://doi.org/10.1107/S2056989019004092/hb7806Isup6.cml
Data collection: APEX3 (Bruker, 2017); cell
SAINT (Bruker, 2017); data reduction: SAINT (Bruker, 2017); 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).C13H24BNO2 | F(000) = 1040 |
Mr = 237.14 | Dx = 0.898 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
a = 34.229 (4) Å | Cell parameters from 1799 reflections |
b = 11.1051 (12) Å | θ = 2.9–25.6° |
c = 9.2922 (10) Å | µ = 0.06 mm−1 |
β = 96.526 (5)° | T = 100 K |
V = 3509.3 (7) Å3 | Plate, colourless |
Z = 8 | 0.32 × 0.30 × 0.10 mm |
Bruker APEXII Ultra diffractometer | 10740 measured reflections |
Radiation source: Micro Focus Rotating Anode, Bruker TXS | 10740 independent reflections |
Double Bounce Multilayer Mirrors monochromator | 8531 reflections with I > 2σ(I) |
Detector resolution: 8.258 pixels mm-1 | θmax = 25.7°, θmin = 1.2° |
φ and ω scans | h = −41→41 |
Absorption correction: multi-scan (TWINABS; Bruker, 2012) | k = −13→13 |
Tmin = 0.300, Tmax = 0.333 | l = −11→11 |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Hydrogen site location: mixed |
R[F2 > 2σ(F2)] = 0.062 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.154 | w = 1/[σ2(Fo2) + (0.0598P)2 + 6.9836P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
10740 reflections | Δρmax = 0.94 e Å−3 |
166 parameters | Δρmin = −0.24 e Å−3 |
0 restraints |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refined as a two-component twin. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.54884 (6) | 0.9933 (2) | 1.1021 (3) | 0.0296 (6) | |
H1 | 0.5259 | 1.0205 | 1.0994 | 0.044* | |
O2 | 0.52308 (7) | 0.9168 (2) | 0.8929 (2) | 0.0373 (7) | |
N1 | 0.59334 (7) | 0.8289 (2) | 0.8033 (3) | 0.0214 (6) | |
H1A | 0.5763 | 0.7656 | 0.7974 | 0.026* | |
H1B | 0.5825 | 0.8865 | 0.7416 | 0.026* | |
C9 | 0.61930 (9) | 0.7507 (3) | 0.5864 (3) | 0.0203 (7) | |
H9A | 0.5993 | 0.6859 | 0.5806 | 0.024* | |
H9B | 0.6077 | 0.8209 | 0.5313 | 0.024* | |
C2 | 0.63037 (8) | 0.7867 (3) | 0.7461 (3) | 0.0172 (7) | |
C10 | 0.64666 (9) | 0.6768 (3) | 0.8315 (4) | 0.0224 (7) | |
H10A | 0.6267 | 0.6120 | 0.8257 | 0.027* | |
H10B | 0.6536 | 0.6983 | 0.9346 | 0.027* | |
C8 | 0.65553 (9) | 0.7071 (3) | 0.5192 (3) | 0.0213 (7) | |
C11 | 0.68651 (9) | 0.8083 (3) | 0.5324 (4) | 0.0241 (8) | |
H11A | 0.7103 | 0.7806 | 0.4906 | 0.029* | |
H11B | 0.6759 | 0.8793 | 0.4764 | 0.029* | |
C6 | 0.68384 (9) | 0.6335 (3) | 0.7642 (4) | 0.0229 (8) | |
H6 | 0.6951 | 0.5618 | 0.8193 | 0.027* | |
C1 | 0.55232 (10) | 0.9311 (3) | 0.9806 (4) | 0.0219 (8) | |
C4 | 0.69762 (9) | 0.8445 (3) | 0.6898 (4) | 0.0243 (8) | |
C3 | 0.66090 (9) | 0.8865 (3) | 0.7553 (4) | 0.0222 (7) | |
H3A | 0.6681 | 0.9095 | 0.8578 | 0.027* | |
H3B | 0.6498 | 0.9583 | 0.7023 | 0.027* | |
C7 | 0.67253 (9) | 0.5977 (3) | 0.6057 (4) | 0.0225 (7) | |
H7A | 0.6528 | 0.5323 | 0.6002 | 0.027* | |
H7B | 0.6960 | 0.5676 | 0.5639 | 0.027* | |
C5 | 0.71424 (9) | 0.7332 (3) | 0.7751 (4) | 0.0277 (8) | |
H5A | 0.7383 | 0.7050 | 0.7354 | 0.033* | |
H5B | 0.7214 | 0.7551 | 0.8780 | 0.033* | |
C13 | 0.64387 (10) | 0.6749 (3) | 0.3590 (4) | 0.0298 (9) | |
H13A | 0.6244 | 0.6099 | 0.3522 | 0.045* | |
H13B | 0.6672 | 0.6484 | 0.3157 | 0.045* | |
H13C | 0.6326 | 0.7458 | 0.3071 | 0.045* | |
C12 | 0.72819 (10) | 0.9460 (3) | 0.6973 (5) | 0.0397 (10) | |
H12A | 0.7515 | 0.9185 | 0.6543 | 0.060* | |
H12B | 0.7358 | 0.9683 | 0.7988 | 0.060* | |
H12C | 0.7169 | 1.0162 | 0.6438 | 0.060* | |
B1 | 0.59514 (12) | 0.8823 (4) | 0.9644 (4) | 0.0295 (10) | |
H1C | 0.6174 (10) | 0.964 (3) | 0.966 (4) | 0.042 (10)* | |
H1D | 0.6026 (11) | 0.810 (3) | 1.038 (4) | 0.050 (11)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0235 (12) | 0.0335 (13) | 0.0342 (14) | −0.0008 (11) | 0.0140 (12) | −0.0136 (11) |
O2 | 0.0334 (14) | 0.0620 (17) | 0.0167 (12) | 0.0240 (13) | 0.0038 (12) | −0.0048 (13) |
N1 | 0.0202 (14) | 0.0169 (13) | 0.0280 (15) | 0.0034 (11) | 0.0062 (12) | 0.0043 (12) |
C9 | 0.0237 (18) | 0.0150 (16) | 0.0222 (17) | 0.0018 (13) | 0.0026 (15) | 0.0029 (15) |
C2 | 0.0149 (16) | 0.0182 (16) | 0.0190 (16) | 0.0039 (13) | 0.0043 (14) | −0.0018 (14) |
C10 | 0.0236 (18) | 0.0213 (17) | 0.0230 (17) | 0.0000 (14) | 0.0062 (15) | 0.0018 (15) |
C8 | 0.0238 (18) | 0.0177 (16) | 0.0227 (18) | 0.0022 (14) | 0.0046 (15) | 0.0007 (15) |
C11 | 0.0225 (18) | 0.0206 (17) | 0.032 (2) | 0.0023 (14) | 0.0134 (16) | 0.0027 (16) |
C6 | 0.0221 (17) | 0.0197 (16) | 0.0268 (18) | 0.0032 (14) | 0.0027 (15) | 0.0045 (15) |
C1 | 0.030 (2) | 0.0181 (17) | 0.0183 (17) | 0.0013 (14) | 0.0046 (16) | 0.0034 (15) |
C4 | 0.0172 (17) | 0.0215 (17) | 0.035 (2) | −0.0027 (14) | 0.0082 (16) | −0.0072 (16) |
C3 | 0.0238 (18) | 0.0193 (17) | 0.0235 (17) | −0.0012 (14) | 0.0024 (15) | −0.0002 (15) |
C7 | 0.0214 (18) | 0.0187 (16) | 0.0287 (17) | 0.0021 (14) | 0.0079 (16) | −0.0043 (16) |
C5 | 0.0170 (17) | 0.037 (2) | 0.0290 (19) | 0.0053 (15) | 0.0007 (16) | −0.0096 (18) |
C13 | 0.033 (2) | 0.033 (2) | 0.023 (2) | 0.0073 (17) | 0.0038 (16) | 0.0011 (17) |
C12 | 0.027 (2) | 0.036 (2) | 0.058 (3) | −0.0085 (17) | 0.012 (2) | −0.012 (2) |
B1 | 0.025 (2) | 0.037 (3) | 0.028 (2) | 0.0001 (19) | 0.0062 (18) | −0.011 (2) |
O1—H1 | 0.8400 | C6—H6 | 1.0000 |
O1—C1 | 1.340 (4) | C6—C7 | 1.532 (5) |
O2—C1 | 1.227 (4) | C6—C5 | 1.515 (4) |
N1—H1A | 0.9100 | C1—B1 | 1.586 (5) |
N1—H1B | 0.9100 | C4—C3 | 1.530 (4) |
N1—C2 | 1.504 (4) | C4—C5 | 1.541 (4) |
N1—B1 | 1.605 (5) | C4—C12 | 1.535 (4) |
C9—H9A | 0.9900 | C3—H3A | 0.9900 |
C9—H9B | 0.9900 | C3—H3B | 0.9900 |
C9—C2 | 1.542 (4) | C7—H7A | 0.9900 |
C9—C8 | 1.530 (4) | C7—H7B | 0.9900 |
C2—C10 | 1.525 (4) | C5—H5A | 0.9900 |
C2—C3 | 1.520 (4) | C5—H5B | 0.9900 |
C10—H10A | 0.9900 | C13—H13A | 0.9800 |
C10—H10B | 0.9900 | C13—H13B | 0.9800 |
C10—C6 | 1.557 (4) | C13—H13C | 0.9800 |
C8—C11 | 1.541 (4) | C12—H12A | 0.9800 |
C8—C7 | 1.535 (4) | C12—H12B | 0.9800 |
C8—C13 | 1.539 (5) | C12—H12C | 0.9800 |
C11—H11A | 0.9900 | B1—H1C | 1.19 (3) |
C11—H11B | 0.9900 | B1—H1D | 1.07 (4) |
C11—C4 | 1.523 (5) | ||
C1—O1—H1 | 109.5 | O2—C1—O1 | 118.8 (3) |
H1A—N1—H1B | 106.9 | O2—C1—B1 | 125.8 (3) |
C2—N1—H1A | 107.3 | C11—C4—C3 | 109.6 (3) |
C2—N1—H1B | 107.3 | C11—C4—C5 | 108.6 (3) |
C2—N1—B1 | 120.0 (3) | C11—C4—C12 | 109.4 (3) |
B1—N1—H1A | 107.3 | C3—C4—C5 | 108.2 (3) |
B1—N1—H1B | 107.3 | C3—C4—C12 | 110.1 (3) |
H9A—C9—H9B | 108.1 | C12—C4—C5 | 110.8 (3) |
C2—C9—H9A | 109.5 | C2—C3—C4 | 110.2 (2) |
C2—C9—H9B | 109.5 | C2—C3—H3A | 109.6 |
C8—C9—H9A | 109.5 | C2—C3—H3B | 109.6 |
C8—C9—H9B | 109.5 | C4—C3—H3A | 109.6 |
C8—C9—C2 | 110.7 (2) | C4—C3—H3B | 109.6 |
N1—C2—C9 | 107.2 (2) | H3A—C3—H3B | 108.1 |
N1—C2—C10 | 109.8 (2) | C8—C7—H7A | 109.7 |
N1—C2—C3 | 110.8 (2) | C8—C7—H7B | 109.7 |
C10—C2—C9 | 109.2 (2) | C6—C7—C8 | 109.7 (3) |
C3—C2—C9 | 109.6 (3) | C6—C7—H7A | 109.7 |
C3—C2—C10 | 110.2 (2) | C6—C7—H7B | 109.7 |
C2—C10—H10A | 110.1 | H7A—C7—H7B | 108.2 |
C2—C10—H10B | 110.1 | C6—C5—C4 | 109.9 (3) |
C2—C10—C6 | 107.8 (3) | C6—C5—H5A | 109.7 |
H10A—C10—H10B | 108.5 | C6—C5—H5B | 109.7 |
C6—C10—H10A | 110.1 | C4—C5—H5A | 109.7 |
C6—C10—H10B | 110.1 | C4—C5—H5B | 109.7 |
C9—C8—C11 | 108.6 (3) | H5A—C5—H5B | 108.2 |
C9—C8—C7 | 108.3 (3) | C8—C13—H13A | 109.5 |
C9—C8—C13 | 109.6 (3) | C8—C13—H13B | 109.5 |
C7—C8—C11 | 108.6 (3) | C8—C13—H13C | 109.5 |
C7—C8—C13 | 111.4 (3) | H13A—C13—H13B | 109.5 |
C13—C8—C11 | 110.3 (3) | H13A—C13—H13C | 109.5 |
C8—C11—H11A | 109.4 | H13B—C13—H13C | 109.5 |
C8—C11—H11B | 109.4 | C4—C12—H12A | 109.5 |
H11A—C11—H11B | 108.0 | C4—C12—H12B | 109.5 |
C4—C11—C8 | 111.3 (3) | C4—C12—H12C | 109.5 |
C4—C11—H11A | 109.4 | H12A—C12—H12B | 109.5 |
C4—C11—H11B | 109.4 | H12A—C12—H12C | 109.5 |
C10—C6—H6 | 109.0 | H12B—C12—H12C | 109.5 |
C7—C6—C10 | 109.7 (3) | N1—B1—H1C | 104.6 (18) |
C7—C6—H6 | 109.0 | N1—B1—H1D | 107 (2) |
C5—C6—C10 | 109.5 (3) | C1—B1—N1 | 106.1 (3) |
C5—C6—H6 | 109.0 | C1—B1—H1C | 109.7 (16) |
C5—C6—C7 | 110.5 (3) | C1—B1—H1D | 111 (2) |
O1—C1—B1 | 115.4 (3) | H1C—B1—H1D | 118 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···O2i | 0.84 | 1.82 | 2.662 (3) | 176 |
N1—H1B···O1ii | 0.91 | 2.11 | 3.011 (3) | 171 |
Symmetry codes: (i) −x+1, −y+2, −z+2; (ii) x, −y+2, z−1/2. |
Acknowledgements
Funding for this research was provided by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant No. P20GM103395. The content is solely the responsibility of the authors and does not necessarily reflect the official views of the NIH.
Funding information
Funding for this research was provided by: National Institutes of Health, National Institute of General Medical Sciences (grant No. P20GM103395).
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