FK506-binding protein ligands: Structure-based design, synthesis, and neurotrophic/neuroprotective properties of substituted 5,5-dimethyl-2-(4- thiazolidine)carboxylates

Article abstract of DOI:10.1021/jm0502384

Structure-based design and discovery of novel neuroimmunophilin FK506-binding protein (FKBP) ligands were pursued in the present study. The binding mode of the known FKBP ligand 1 (3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate) in complex with FKBP12 was investigated using LUDI simulation and upon which a novel scaffold structure predicted to possess improved binding affinity was designed. A virtual combinatorial library composed of diverse combinations of two substituted groups was constructed using Project Library, followed by an automated screening of the library against the ligand binding site on FKBP52 using DOCK. Forty-three candidate compounds that displayed favorable binding with the receptor were identified and synthesized. The neurotrophic activity of the candidate compounds was evaluated on chick dorsal root ganglion cultures in vitro. As a result, 15 compounds exhibited positive effects on ganglion neurite outgrowth in the presence of 0.15 ng/mL NGF, among which 7 compounds at testing concentrations of 1 pM and 100 pM showed greater efficacy than 1 at 100 pM. Compound 18 (3-(3-pyridyl)-1-propyl (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2- dioxobutyl)-2-(4-thiazolidine)carboxylate) afforded the most potent effect in promoting the processes of neurite outgrowth and which was in a concentration-dependent manner from 1 pM to 100 pM. Half-maximal effect occurred at about 10 pM. Moreover, 18 at a dosage of 10 mg/kg was found to be significantly neuroprotective in a mouse peripheral sympathetic nerve injury model induced by 8 mg/kg 6-hydroxydopamine. This study further suggests the clinical potential of novel FKBP ligands as a new therapeutic approach in the treatment of neurodegenerative disorders, such as Parkinson's disease.

Full text of DOI:10.1021/jm0502384

J. Med. Chem. 2006, 49, 4059-4071
4059
Articles
FK506-Binding Protein Ligands: Structure-Based Design, Synthesis, and Neurotrophic/
Neuroprotective Properties of Substituted 5,5-Dimethyl-2-(4-thiazolidine)carboxylates
Liqin Zhao,*,§ Wei Huang, Hongying Liu, Lili Wang, Wu Zhong, Junhai Xiao, Yuandong Hu, and Song Li*
Laboratory of Computer-Aided Drug Design & DiscoVery, Beijing Institute of Pharmacology and Toxicology, 27 Taiping Road,
Beijing 100850, China
ReceiVed March 15, 2005
Structure-based design and discovery of novel neuroimmunophilin FK506-binding protein (FKBP) ligands
were pursued in the present study. The binding mode of the known FKBP ligand 1 (3-(3-pyridyl)-1-propyl
(2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidinecarboxylate) in complex with FKBP12 was investigated
using LUDI simulation and upon which a novel scaffold structure predicted to possess improved binding
affinity was designed. A virtual combinatorial library composed of diverse combinations of two substituted
groups was constructed using Project Library, followed by an automated screening of the library against the
ligand binding site on FKBP52 using DOCK. Forty-three candidate compounds that displayed favorable
binding with the receptor were identified and synthesized. The neurotrophic activity of the candidate
compounds was evaluated on chick dorsal root ganglion cultures in vitro. As a result, 15 compounds exhibited
positive effects on ganglion neurite outgrowth in the presence of 0.15 ng/mL NGF, among which 7 compounds
at testing concentrations of 1 pM and 100 pM showed greater efficacy than 1 at 100 pM. Compound 18
(3-(3-pyridyl)-1-propyl (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxobutyl)-2-(4-thiazolidine)carboxylate) af-
forded the most potent effect in promoting the processes of neurite outgrowth and which was in a
concentration-dependent manner from 1 pM to 100 pM. Half-maximal effect occurred at about 10 pM.
Moreover, 18 at a dosage of 10 mg/kg was found to be significantly neuroprotective in a mouse peripheral
sympathetic nerve injury model induced by 8 mg/kg 6-hydroxydopamine. This study further suggests the
clinical potential of novel FKBP ligands as a new therapeutic approach in the treatment of neurodegenerative
disorders, such as Parkinson’s disease.
Introduction
suggesting that FKBP12 and other immunophilins may also play
a pivotal role in regulating neural functions in the nervous
system. Subsequently, spurred by the first report of the
neuroregenerative effect of FK506 as demonstrated by its
enhancement of neurite outgrowth in cultures of rat PC12
pheochromocytoma cells and sensory ganglia11 and a following
study published later in the same year that demonstrated the
neuroprotective effect of FK506 in an animal model of focal
cerebral ischaemia,12 the functional role of immunophilins in
the nervous system are extensively investigated in the past
decade. Solid evidence from both in vitro cultures and in vivo
animal studies raise the possibility of applying immunophilins,
in particular FKBPs, as novel therapeutic targets for the
development of effective intervention therapies against neuro-
logical disorders, particularly neurodegenerative diseases (see
reviews13-18). Nevertheless, immunosuppressive ligands target-
ing immunophilins have been clinically linked with a number
of adverse effects when administered chronically.19-21 A strategy
that could circumvent many of the problematic aspects of these
immunosuppressants is the development of an mimic molecule
designed to activate the neurotrophic and neuroprotective
mechanisms associated with immunophilins in the nervous
system while avoiding the interference in the immune system,
so-called nonimmunosuppressive neuroimmunophilin ligand
(NIL).22-24
Immunophilins, including cyclophilins,1 FK506-binding pro-
teins (FKBPs),2 and parvulins,3 are a family of phylogenically
conserved binding proteins, possessing peptidyl prolyl cis-trans
isomerase activity that is essential for protein folding.4,5 Im-
munophilins were originally discovered and studied in the
immune system. It is well established that the immunosuppres-
sive effects of cyclosporin A (CsA) and FK506, which have
been widely used clinically in inhibiting immune responses in
organ transplantation, result from binding to their cognate
immunophilin receptors, cyclophilin A for CsA and FKBP12
(the 12-kDa FKBP) for FK506.6 The immunosuppressant-
immunophilin binary complex in turn binds to and inactivates
the Ca2+/calmodulin-dependent serine/threonine protein phos-
phatase calcineurin,7,8 leading to blockage of the translocation
of the nuclear factor of activated T-cells into the nucleus and
ensuing inhibition of interleukin-2 gene transcription which is
necessary for T-cell activation.9
Beyond the immune system, immunophilins are found
enriched in neurons as well. Snyder and his colleagues first
discovered that the FKBP12 level in the rat brain is 10-50-
fold higher than its expression in the immune system,10
* Corresponding authors: Dr. Liqin Zhao, Tel: 323-4421436; Fax: 323-
2247473; E-mail: liqinz@usc.edu. Dr. Song Li, Tel: 86-10-66931250;
Fax: 86-10-68214653; E-mail: lis@nic.bmi.ac.cn.
FK506 is a natural macrolide product composed of two
domain structures, the “FKBP-binding domain” binds to FKBPs
and the “effector domain” binds to calcineurin (see Figure 1).25
§ Current address: Department of Molecular Pharmacology & Toxicol-
ogy, School of Pharmacy, University of Southern California, 1985 Zonal
Ave., Pharmaceutical Sciences Center, Los Angeles, CA 90089.
10.1021/jm0502384 CCC: $33.50 © 2006 American Chemical Society
Published on Web 06/21/2006

4060 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14
Zhao et al.
Figure 1. FK506 is composed of two domain structures, the “FKBP-binding domain” which binds to FKBP and the “effector domain” which binds
to calcineurin. Small molecule 1 is a mimic structure of the “FKBP-binding domain” of FK506. Structural analogue 18 exhibited enhanced binding
affinity to FKBP protein and greater therapeutic potential than 1.
It is suggested that the neural functions of FK506 are conferred
only by its “FKBP-binding domain” and independent of
calcineurin inhibition associated with the “effector domain”.26
In light of this profound notion, a number of novel analogues
of FK506 with NIL potential have been developed from different
research groups. One typical example is the emergence of a
small molecule, 1 (3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-
1,2-dioxopentyl)-2-pyrrolidinecarboxylate), a mimic structure
of the “FKBP-binding domain” of FK506 and devoid of the
calcineurin binding domain as present in FK506 (see Figure
1).27 Multiple studies have demonstrated that 1 is a highly potent
neurotrophic and neuroprotective molecule in various in vitro
and in vivo model systems but has no effect in the immune
system,27-33 further suggesting that the inhibition of immune
responses and promotion of neural functions associated with
an immunophilin ligand can be separated. Unfortunately, some
of the positive data on 1 were questioned by Harper et al. who
failed to reproduce the corresponding activities.34 1 was also
shown to be ineffective in some other neural systems.35-37 One
possible explanation for the decreased activity of 1 in the
nervous system in comparison with FK506 may originate from
its much weaker binding affinity to FKBP protein, although the
costructure of 1 in complex with FKBP12, determined by
heteronuclear NMR spectroscopy, showed that 1 exhibits a
binding mode analogous to that observed for FK506.38
Several isoforms of FKBP with disparate molecular size exist
in the nervous system. Using a FKBP12-knockout mice model
and a mouse monoclonal antibody that does not interact with
FKBP12, Gold et al. first discovered that the high-molecular
weight FKBP52 (also known as FKBP59 or hsp56), rather than
FKBP12, mediated the neurotrophic action of FK506.39,40 In
agreement with this finding, Guo et al. found that FK506
afforded a similar protective effect against MPP+ toxicity in
cultured dopaminergic neurons derived from FKBP12-knockout
mice.41 Further, FK506 and 1 were demonstrated to exhibit
equipotent neuroprotection in both SH-SY5Y and U251 human
cells, although FKBP12 mRNA expression was only detected
in SH-SY5Y cells.42 Upon ligand binding to FKBP52, a
chaperone component of mature steroid receptor complex, a
subsequent “gain-of-function” takes place following the disrup-
tion of the chaperone complex, involving the dissociation of
p23 from hsp90 and the ensuing extracellular signal-regulated
kinase (ERK1/2) activation.43
a result, a series of substituted 5,5-dimethyl-2-(4-thiazolidine)-
carboxylate derivatives were synthesized and evaluated for their
neurotrophic and neuroprotective efficacy in vitro and in vivo,
respectively.
Results
Scaffold Design. To determine the molecular basis accounting
for the week binding of 1 to FKBP and rationally design novel
ligands with enhanced binding affinity, we initiated this study
with a computer-aided analysis on the 3D bound structure of 1
in complex with FKBP12. LUDI, an automated fragment-based
suggestive program for the de novo design of protein ligands
developed by Bolm,44 was applied. The basic idea of LUDI is
to construct novel protein ligands by linking with a suitable
spacer the molecular fragments which are positioned into the
active site of a protein in such a way that hydrogen bonds can
be formed with the protein and hydrophobic pockets are filled
with hydrophobic groups.45 In particular, LUDI can be used to
provide rational suggestions for the modification of a known
ligand by improving the favorable contacts with the protein.45
Computation was performed on a SGI O2 R10000 work-
station equipped with the IRIX operating system (Silicon
Graphic Inc.). The 3D complex structure of 1 with FKBP12
(PDB ID: 1F40)38 was imported into the graphic modeling
program InsightII 98.0 (Accelrys Inc.). By running LUDI
calculation following the structural fixation and energy mini-
mization, the bound structure of 1 as a template scaffold in the
context of FKBP12 was examined in a link mode. Computa-
tional results indicated that there is an unoccupied space between
the pyrrolidine ring of 1 and the vicinal protein surface but that
can be saturated by the introduction of two methyl groups on
the 5-position of the ring structure, which may improve the
ligand binding to the protein through enhanced hydrophobic
interactions. In addition, we observed that the replacement of
the carbon atom on the 4-position of the pyrrolidine ring of 1
with an oxygen or sulfur atom leads to the formation of a
potential polar interaction with the nearby residue Tyr-26
mediated by a middle water molecule. Based on these findings
and consideration of structural stability, a novel scaffold
structure presented in Scheme 1 was designed which retains all
the favorable structural requirements for binding in FK506 and
1 but is expected to have increased FKBP binding affinity
compared to 1.
In view of the mechanistic significance of FKBP52 in
mediating neuroimmunophilin ligands-inducible promotion of
neuroregeneration and neuronal survival, in the present study,
by means of computer-aided structure-based approach, we
sought to design and discover novel ligands targeting FKBP52
that are expected to hold better therapeutic promise than 1. As
Library Construction. Since both substituted groups R1 and
R2 in the scaffold structure (see Scheme 1) would make pivotal
contributions to ligand binding to the protein, a virtual com-
pound library containing diverse R1 and R2 combinations was
constructed using Project Library 2.0 (MDL Information
Systems Inc.), a multifunctional combinatorial library construc-

FK506-Binding Protein Ligands
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14 4061
Scheme 1a
a Reagents and conditions: (a) (CH3)2CO, reflux, 1 h; (b) C2H5OCOCOCl, (C2H5)3N, (C2H5)2O, 0 °C, 1.5 h; (c) R1MgCl or R1MgBr, THF, -78 °C, 5
h; (d) 1 N LiOH, MeOH, 0 °C, 30 min; room temperature, overnight; 1 N HCl; (e) R2OH, DCC, DMAP, camphorsulfonic acid, CH2Cl2, room temperature,
overnight.
Figure 2. A: Costructure of hFKBP12 bound with FK506. B: Site points on FKBP52-I represented with red spheres. The molecular surface
which was used to produce spheres was calculated by the program MS, available from Quantum Chemistry Program Exchanger.
tion program46 as described below. The constructed library was
then screened to identify the potential candidate compounds that
display favorable binding to the protein active site.
role of FKBP52 in mediating the neurotrophic and neuro-
protective effects of NILs,39,40,50 we chose FKBP52 as the
docking target.
According to the proposed synthetic route for the preparation
of target compounds (see Scheme 1), R1 and R2 can be attached
to the root structural moiety by the Grignard reaction and
esterification, respectively. Therefore, the first step in the library
construction was to select the appropriate Grignard reagents
(R1MgCl or R1MgBr) and alcohols (R2OH) from an Available
Chemical Directory (MDL Information Systems, Inc.). By using
the building-blocks clipper, the structural lists of selected
reagents were processed into building blocks that were then used
as Rgroup members by clipping the structures and adding
attachment points. Then, the combinatorial library was built
based on the root structure and Rgroup member lists, which
was further expanded by enumeration, a process of automatic
generation of fully specified structures. Finally, the constructed
library was exported as a SDF file, which was then converted
to a SYBYL MOL2 file that can be read by DOCK. As a result,
a collection of 57120 virtual compounds constructed by 51
Grignard fragments and 2100 alcoholic fragments, containing
the information about atom types and charges, was built for
the next stage of computer screening.
Since the first N-terminal domain in FKBP52 (FKBP52-I)
displays high sequence and structure similarity to FKBP12 (52%
of sequence identity), especially among the residues defining
the active site,51 the high-resolution X-ray structure of human
FKBP12 complexed with FK506 (PDB ID: 2FKE)52 was used
as a template for the determination of the binding site on
FKBP52-I. By superimposing the NMR solution structure of
FKBP52-I (PDB ID: 1ROT)53 with the costructure of FKBP12
complexed with FK506 based on alpha carbon atoms, the
corresponding binding site of FK506 on the surface of FKBP52-I
was designated as the docking site and represented as a cluster
of 33 site-points (as shown in Figure 2), which were generated
by the sphere generation accessory program, SPHGEN, inte-
grated into the DOCK program suite. The identified binding
site was then gridded by the program GRID, which saves
information about the steric and electrostatic environment at
each point on a grid.
The fitness of molecules onto the FKBP52-I surface binding
site was ranked in turn by three independent scoring functions
integrated into DOCK. In detail, the entire collection of the
constructed virtual library containing 57120 compounds was
first screened by a contact score function, which provides a
simple assessment of shape complementarity between the ligand
and the protein. As a result, 10000 top-scoring compounds with
the best orientation were saved. Then, the orientation of each
of the 10000 compounds was searched and evaluated again
based on an energy score function, a measurement of the extent
of van der Waals and electrostatic interaction between the ligand
Computer Screening. DOCK 4.0 (University of California
at San Francisco; http://www.cmpharm.ucsf.edu/kuntz/), an
automated molecular docking and database screening program
developed by Kuntz et al.,47,48 was used. The core of the DOCK
searching and scoring algorithm is to superimpose the ligand
atoms onto predefined site-points that map out the negative
image of the protein binding site and evaluate the com-
plementarity between the two.49 On the basis of the potential

4062 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14
Zhao et al.
and the protein. The resulting 1000 top-scoring compounds were
further tailored by a chemical score function to enhance
recognition of chemical complementarity. Finally, following a
modified procedure of Li et al.,54 the top 500 compounds yielded
from the chemical search were visually screened three times in
the context of FKBP52-I using the InsightII 98.0 software
package. After taking the molecular weight distribution, drug-
like property, cost and availability of reagents, and synthetic
accessibility into account, a subset of 43 candidate compounds
were chosen to be synthesized.
It should be pointed out that some compounds in the library
have one or more chiral centers. For these compounds, only
one chiral center was examined during the docking process. In
addition, for those flexible compounds having multiple possible
conformations, a systematic search was performed with the
available computational power. A minimization procedure
allowing on-the-fly adjustment of a compound’s orientation and
conformation was also performed, aiming at improving the
intermolecular interactions.
Figure 3. Effects of positive compounds on neurite outgrowth in DRG
cultures. DRGs were treated with test compounds at 1 pM or 100 pM
in the presence of 0.15 ng/mL NGF, and outgrowth was observed at
48 h. The control group was treated with the same amount of NGF. At
either one or both concentrations, 15 test compounds potentiated neurite
outgrowth in DRGs compared to the NGF only treated control group.
Of them, compounds 14, 17, 18, 20, 24, 27, and 29 exhibited greater
effects at both 1 pM and 100 pM than 1 at 100 pM. Data shown were
the average results from two separate experiments. A total of 15-18
ganglion cultures for each group were included in each experimental
run.
Chemistry. Candidate compounds can be prepared in several
ways. A relatively simple and easy route was described in
Scheme 1. Ethyl 5,5-dimethyl (2S)-2-(4-thiazolidine)carboxylate
(2) was prepared following an established procedure,55 through
the simple treatment of commercially available optically active
L-cysteine ethyl ester hydrochloride and acetone under refluxing
condition. 2 was acylated by ethyl oxalyl chloride in the presence
of triethylamine to afford ethyl 5,5-dimethyl (2S)-1-(1,2-dioxo-
2-ethoxyethyl)-2-(4-thiazolidine)carboxylate. The ethoxy group
attached to the dicarbonyl moiety in 3 was then nucleophilically
substituted by alkylating group under treatment with Grignard
reagent, at the reaction temperature -78 °C to reduce the
occurrence of side substitution on the monocarbonyl ester
moiety. The resulting product (4) underwent saponification by
1 N lithium hydroxide in methanol and then acidified by 1 N
hyhydrochloric acid to yield the corresponding substituted (2S)-
2-(4-thiazolidine)carboxylic acid (5), which was further reacted
with various alcohols following a routine procedure to give the
target compounds (6-48).
Biological Results. The neurotrophic activity of the target
compounds was assessed in vitro in chick dorsal root ganglion
(DRG) cultures following a previously described procedure of
Lyons et al.11 Due to the poor water solubility, the compounds
were first dissolved in analytically pure DMSO at 1 mM and
then diluted in DMEM to the final concentrations for the
bioassays, in which the concentrations of DMSO were less than
10-7 M and had no detectable effects on the DRGs. The vehicle-
treated control cultures received the same amount of DMSO as
present in the highest concentrations of test compounds.
Figure 4. Compound 18 increased the neurite outgrowth in DRG
cultures in a concentration-dependent manner. DRGs were treated with
NGF (0.15 ng/mL) alone (control group) or in the presence of
compound 18 (0.1, 1, 10, 100, or 1000 pM), and outgrowth was
observed at 48 h. At all test concentrations, compound 18 significantly
increased neurite outgrowth in DRGs compared to NGF alone-treated
control cultures. Between 1 pM and 100 pM, 18 exerted a concentration-
dependent increase of neurite processes with the maximal response at
100 pM. The activity decreased at a higher concentration (1000 pM).
1 at 100 pM only induced a slight potentiation on neurite outgrowth
that was elicited by the same amount of NGF. Data are represented as
mean ( SEM, n g 3. * P < 0.05 and ** P < 0.01 compared to NGF
alone-treated control cultures.
To determine an appropriate concentration for evaluation, a
preliminary screening on several random compounds, at a wide
concentration range from picomolar order to nanomolar order,
was conducted. As a result, two concentrations of 1 pM and
100 pM, at which most test compounds displayed positive
effects on neurite outgrowth in DRGs, were used for the
subsequent biological screening. In addition, to quickly highlight
those lead candidate compounds with improved therapeutic
potential compared to 1 for further detailed analyses, two
separate experimental runs on all target compounds at both
concentrations were conducted. A third run was performed if
the data yielded from the first two experiments exhibited big
variance. The average results, as shown in Figure 3, revealed
that about one-third out of a total of 43 test compounds promoted
neurite outgrowth in DRGs in the presence of nerve growth
factor (NGF) at a concentration of 0.15 ng/mL, which was used
to induce small neurite processes in DRGs. Compounds 14, 17,
18, 20, 24, 27, and 29 exhibited greater efficacy at both 1 pM
and 100 pM than 1 at 100 pM.
As demonstrated in Figure 3, compound 18 showed the most
potent effect on the outgrowth of chicken sensory ganglia. An
extensive investigation of the neurotrophic efficacy and con-
centration response profile of compound 18 was then performed
(see Figures 4 and 5). As a result, compound 18 elicited a
significant augmentation on the ganglion processes, even at a
low concentration of 0.1 pM. Between 1 pM and 100 pM, 18

FK506-Binding Protein Ligands
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14 4063
Figure 5. Representative micrographs of chick DRGs grown with NGF (0.15 ng/mL) alone or in the presence of compound 18 (1, 10, or 100 pM).
(A) NGF at 0.15 ng/mL alone only elicited small neurite processes; (B) Compound 18 at 1 pM increased neurite processes that was elicited by
NGF; (C) Compound 18 at 10 pM exerted greater potentiation on neurite processes than that observed at 1 pM; (D) Compound 18 at 100 pM
showed the maximal effects on the number and length of neurite processes compared to NGF alone-treated cultures.
Table 1. Effects of FK506 and Compound 18 on Norepinephrine (NE)
demonstrated a markedly concentration-dependent increase of
Content in Mouse Submandibular Glands Following Peripheral
gonglion processes with a maximal response at 100 pM. The
half-maximal effect occurred at about 10 pM, and the activity
decreased at a higher concentration (1 nM). 1 at 100 pM alone
exerted a slight potentiation of neurite outgrowth induced by
0.15 ng/mL NGF. In the absence of exogenously added NGF,
however, 18 and related compounds in the present study failed
to promote neurite outgrowth in DRGs.
Sympathetic Nerve Injury Induced by Intraperitoneal Injection of
6-Hydroxydopamine (6-OHDA)a
treatment
vehicle/vehicle
6-OHDA/vehicle
6-OHDA/FK506, 2 mg/kg
6-OHDA/18, 10 mg/kg
NE content (µg/g wet weight)
2.38 ( 0.11
1.77 ( 0.21##
2.33 ( 0.28**
2.31 ( 0.34**
a Mice were treated with FK506 (2 mg/kg, s.c.) or compound 18 (10
mg/kg, s.c.) 4 h prior to intraperitoneal injection of 6-OHDA (8 mg/kg)
and daily for the subsequent 4 days following the 6-OHDA treatment.
Animals were sacrificed 2 weeks after the last treatment. The NE content
in mouse submandibular glands was measured by HPLC-ECD. Data are
Encouraged by its promising in vitro neurotrophic activity,
compound 18 was further evaluated for its neuroprotective
activity in vivo. A standard mouse peripheral sympathetic nerve
injury model induced by 6-hydroxydopamine (6-OHDA)56 was
employed and FK506 was used as a positive control. The
neuroprotective effect of compound 18 was indirectly assessed
by the measurement of norepinephrine (NE) content in mouse
submandibular glands following the intraperitoneal injection of
6-OHDA. Results from these analyses demonstrated that the
degree of injury of peripheral sympathetic nerves in mice was
relevant to the dose of 6-OHDA administered. An intraperitoneal
injection of 8 mg/kg 6-OHDA in mice induced a significant
decrease of NE content in submandibular glands, P < 0.01
compared to the vehicle/vehicle-treated control groups.
Data shown in Table 1 demonstrated that pretreatment of mice
with compound 18 at 10 mg/kg s.c. 4 h prior to 6-OHDA
treatment and the subsequent daily treatment for 4 days
following the lesion elicited a pronounced increase in the NE
content in mouse submandibular glands compared to 6-OHDA/
vehicle-treated control groups (P < 0.01), indicating a significant
protection of peripheral sympathetic nerves against injury
induced by 6-OHDA. This effect was comparable to that induced
by 2 mg/kg FK506.
##
represented as mean ( SEM, n g 3. P < 0.01 compared to vehicle/
vehicle-treated animals and ** P < 0.01 compared to 6-OHDA/vehicle-
treated animals.
investigation of the bound structure of the known neuro-
immunophilin ligand 1 in complex with FKBP12 in a computer
graphical environment, by sequentially applying a number of
computation-based design programs, in the present study, we
efficiently designed a novel scaffold structure that was predicted
to possess improved binding affinity to FKBP, and then
identified 43 potential candidates from a large compound
collection. Fifteen compounds exhibited positive neurotrophic
effects on neurite outgrowth in DRGs, 7 of which demonstrated
greater efficacy at 1 pM and 100 pM than 1 at 100 pM,
indicating the effectiveness of the state-of-the-art computational
chemistry and modeling-guided drug design approaches in the
development of potential therapies for human diseases. Computer-
aided design and screening provide an efficient and automated
strategy to highlight a small group of candidate hits from a large
number of compounds for actual biological investigation.
Although much remains to be determined with respect to the
underlying downstream pathways following the binding to
FKBP52 that lead to promotion of neuroregeneration and the
neuronal defense system afforded by FK506 and related
neuroimmunophilin ligands in the nervous system, the current
Discussion
Along with rapid advances in the fields of structural biology
and computational graphics, computer-aided structure-based
drug design has increasingly become an important strategy in
the development of new pharmaceuticals. Starting with the

4064 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14
Zhao et al.
state of knowledge is sufficient to demonstrate the clinical
potential of these compounds as a novel therapeutic approach
for the treatment of neurodegenerative disorders. As illustrated
in the present study, compound 18 exhibited significant neu-
rotrophic effects within a wide range of concentrations on
sensory ganglia by increasing their sensitivity to NGF. NGF,
at a concentration of 0.15 ng/mL, only induced some small
neurite processes, which were markedly increased by compound
18 even at a low concentration of 0.1 pM. The observation that
compound 18 at 0.1 pM was more effective than it was at 1
pM may imply that distinct molecular mechanisms may be
involved in mediating the promotive effects of this compound
on neurite outgrowth at different concentrations. Furthermore,
compound 18 at a dosage of 10 mg/kg was demonstrated to be
significantly neuroprotective against mice peripheral sympathetic
nerve injury induced by 8 mg/kg of 6-OHDA, which was
comparable to that elicited by 2 mg/kg of FK506. Taken
together, results from both in vitro and in vivo studies indicate
that compound 18 and its structural analogues hold the promise
for further development as potential therapeutics for the treat-
ment of a variety of neurological disorders, including Parkin-
son’s disease. However, it should be noted that the neuro-
protective efficacy of compound 18 was found to be relevant
to the severity of the nerve injury caused by the injection of
different doses of 6-OHDA. When the injection dose of
6-OHDA increased to 10 mg/kg which induced greater damage
to the peripheral sympathetic nerves in mice, the sustained effect
on NE content afforded by compound 18 was not statistically
significant compared to 6-OHDA alone-treated mice, suggesting
that this compound may be more effective in treating mild nerve
injury. In the instance of severe injury, treatment with this
compound alone is probably not sufficient to reverse the nerve
damage induced, for example, by a higher dose of 6-OHDA.
differently when applying these compounds in treating different
neurodegenerative conditions.
A preliminary analysis of the structure-activity relationship
(SAR) of the test compounds revealed that R1 and R2 in the
scaffold structure could be substituted by a variety of structurally
diverse groups, but with a distinct impact on the biological
activity afforded by these compounds. Overall, for R1, aryl
substituted C2-C3 alkyl or alkenyl, i.e., 3-(3-pyridyl)-1-phenyl,
3-phenyl-1-propyl, 3-phenyl-2-(E)-1-propyl, 2-(2-thienyl)-1-
ethyl and 2-(2-chlorophenyl)-1-ethyl, or long chain alkyl or
alkenyl, i.e., 10-decen-1-yl, were favorable to the biological
activity, as exemplified by compounds 14, 17, 18, 20, 24, 27,
and 29, which were found to be highly neurotrophic to neurite
outgrowth in DRGs cultures. In contrast, compounds containing
short alkyl groups for R1, such as pentyl or alkyl substituted
with a cycloalkyl such as 3-cyclohexyl-1-propyl, were less
effective. For R2, either straight or branched lipophilic alkyl
groups with appropriate length, including tert-butyl, 2-methyl-
2-butyl, or n-hexyl, were found to be associated with increased
biological activity. However, long chain alkyl such as n-octyl
was proven to be harmful to the activity of the corresponding
compounds. Although a detailed study of the SAR of these
compounds will be needed, these analyses provided some
insights into the further development of more potent FKBP
ligands for the treatment of neurodegenerative diseases.
Conclusion
The present study demonstrated the effectiveness of the
computer-aided molecular design and virtual screening ap-
proaches in our discovery of novel FKBP ligands that hold the
promise of a novel therapeutic strategy for the treatment of
neurodegenerative disorders, such as Parkinson’s disease. In
comparison with a number of neurotrophic proteins, compounds
designed in this study are readily synthesized and devoid of
the problems associated with large proteins, such as poor
bioavailability and transportation that currently hamper their
clinical application. Moreover, unlike many neurotrophic pro-
teins, such as NGF, which elicit sprouting of normal sensory
neurons,63 compounds presented herein are anticipated to have
little likelihood to induce aberrant sprouting of neuronal
processes. These analyses suggest that these compounds are
encouraging potential prospects for further investigation.
Compound 18 and its analogues, including 1, failed to elicit
neurite outgrowth in DRGs in the absence of exogenously added
NGF, suggesting that the neuroimmunophilin ligands-inducible
neurotrophic activity is dependent upon NGF. In accordance
with this observation, FK506 was found to require the addition
of exogenous NGF as well to promote the neuronal outgrowth
in PC12 cells.11 Gold proposed that the underlying mechanism
mediating the neurotrophic action of neuroimmunophlin ligands
could form a convergence with the known neurotrophic factor
(NTF, e.g. NGF) signal transduction pathway, leading to
potentiated activity over NGF alone, and which may be mediated
by the interaction between hsp90 and MAP kinase/ERK2.40
Tanaka et al. demonstrated that both FK506 and 1 increased
expression of neurotrophic factors, such as the glial cell line-
derived neurotrophic factor and the striatal brain-derived neu-
rotrophic factor, in the substantia nigra of a mouse brain, further
suggesting that NILs-induced neurotrophic action may be at least
partially dependent on NTFs activation.57 In contrast to the
neurotrophic analyses, we found that the neuroprotective activity
of compound 18 against peripheral sympathetic nerve injury
induced by 6-OHDA in mice did not require the presence of
NGF. These observations suggest that the neurotrophic and
neuroprotective effects afforded by this compound and other
related NILs may be mediated by different signaling pathways.
Several studies have demonstrated that NILs-induced neuro-
protection is associated with their glutathione-activating effect
and anti-apoptotic effect.58-60 The rapid induction of heat shock
protein response is proposed to be another component in the
molecular mechanisms that underlie NILs-induced neuro-
protection.16,61,62 These results suggest that it should be treated
Experimental Section
Chemistry. General Methods. Melting points were determined
in open capillary tubes on a RY-1 melting point apparatus and are
uncorrected. 1H NMR spectra were recorded on a Bruker ARX 400
spectrometer or US Varian Unity Inova 600 spectrometer using
tetramethylsilane (TMS) as an internal standard. The splitting pattern
abbreviations are as follows: s ) singlet, d ) doublet, t ) triplet,
q ) quartet, br ) broad, m ) multiplet, dd ) doublet doublet, dt
) doublet triplet, ddd ) doublet doublet doublet, ddt ) doublet
doublet triplet. FAB mass spectra (FAB-MS) and EI high-resolution
mass spectra (EI-HRMS) were recorded on a VG Zabspect mass
spectrometer. Elemental analyses (C, H, N) were performed on a
FISONS-1108 auto analyzer. Column chromatography was per-
formed on silica gel H and analyzed by thin-layer chromatography
using precoated silica gel GF254 plates.
Ethyl (2S)-5,5-Dimethyl-2-(4-thiazolidine)carboxylate Hydro-
chloride (2). A suspension of l-cysteine ethyl ester hydrochloride
(10 g, 53.9 mmol) in dry acetone (150 mL) was refluxed for 1 h,
during which the solid was gradually dissolved. After cooling to
room temperature, the precipitate was collected by filtration, washed
with cold acetone, and dried to afford compound 2 (9.75 g, 80.2%)
as a white crystalline solid: mp 148-150 °C.

FK506-Binding Protein Ligands
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14 4065
Ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-2-(4-thia-
zolidine)carboxylate (3). A stirred suspension of ethyl (2S)-5,5-
dimethyl-2-(4-thiazolidine)carboxylate hydrochloride 2 (1.95 g, 8.64
mmol) in dry ethyl ether (30 mL) was cooled to 0 °C, to which a
solution of ethyl oxalyl chloride (1.77 g, 12.9 mmol) in dry ethyl
ether (10 mL) together with a solution of triethylamine (1.83 g,
18.1 mmol) in dry ethyl ether (20 mL) were added dropwise
separately at a rate to maintain the temperature of the reaction
mixture below 5 °C. After addition the resulting mixture was stirred
at 0 °C for further 1.5 h and then filtered to remove solids. The
organic layer was collected, washed with water, dried over
anhydrous MgSO4, and concentrated in vacuo to afford compound
3 (2.1 g, 84.1%) as a pale yellow oil, which did not require further
purification.
calcd for C23H31NO4S [M]+, 417.1974; found, 417.1967. Anal.
(C23H31NO4S): C, H, N.
3-Phenoxy-1-propyl (2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-di-
oxoethyl)-2-(4-thiazolidine)carboxylate (8). This compound was
prepared from (2S)-5,5-dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-
2-(4-thiazolidine)carboxylic acid 5a (400 mg, 1.34 mmol) and
3-phenoxy-1-propanol (305 mg, 2.01 mmol) in the same procedure
as described in the preparation of compound 6 (440 mg, 75.8%).
1H NMR (400 MHz, CDCl3) δ 1.11-1.38 (m, 6H), 1.64-1.95 (m,
4H), 1.86 (s, 3H), 1.93 (m, 3H), 2.14 (m, 2H), 3.16 (m, 1H), 3.29
(m, 2H), 4.04 (m, 2H), 4.38 (m, 2H), 5.34 (dd, 1H, J ) 3.0, 4.9
Hz), 6.88 (m, 2H), 6.95 (m, 1H), 7.28 (m, 2H). FAB-MS [M +
H]+ ) 434.1 m/e. EI- HRMS: calcd for C23H32NO5S [M + H]+,
434.2001; found, 434.1995. Anal. (C23H31NO5S): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-2-(4-
thiazolidine)carboxylate (4a). A solution of ethyl (2S)-5,5-
dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-2-(4-thiazolidine)carboxyl-
ate 3 (2.5 g, 8.65 mmol) in dry THF (75 mL) was cooled to -80
°C, to which a 2.0 M solution of cyclohexylmagnesium chloride
(5.75 mL, 11.5 mmol) in ethyl ether was added at a rate to maintain
the temperature of the reaction mixture not exceeding -70 °C. The
resulting mixture was stirred at about -80 to -70 °C for additional
5 h and then poured into saturated solution of ammonium chloride
in water (100 mL). After extraction with ethyl acetate, the organic
layer was collected, washed with water, dried over anhydrous
MgSO4, and concentrated in vacuo. The crude material was purified
by column chromatography on silica gel using ethyl acetate-
petroleum ether (1:10) as eluent to afford compound 4a (2.2 g,
77.8%) as a pale yellow oil.
(2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-2-(4-thia-
zolidine)carboxylic Acid (5a). A mixture of ethyl (2S)-5,5-
dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-2-(4-thiazolidine)carbox-
ylate 4a (5.6 g, 17.1 mmol), 1 N LiOH (31 mL), and methanol
(100 mL) was stirred at 0 °C for 30 min and then at room-
temperature overnight. The reaction mixture was acidified to pH 1
with 1 N HCl, diluted with water, and extracted with ethyl acetate.
The organic extracts were collected, washed with saturated brine
solution, dried over anhydrous MgSO4, and concentrated in vacuo
to afford compound 5a (4.5 g, 87.9%) as a white powder solid,
which did not require further purification.
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-
dioxoethyl)-2-(4-thiazolidine)carboxylate (6). A mixture of (2S)-
5,5-dimethyl-1-(2-cyclohexy-1,2-dioxolethyl)-2-(4-thiazolidine)-
carboxylic acid 5a (400 mg, 1.34 mmol), 3-(3-pyridyl)-1-propanol
(275 mg, 2.01 mmol), dicyclohexylcarbodiimide (331 mg, 1.61
mmol), camphorsulfonic acid (94 mg, 0.41 mmol), and 4-(di-
methylamino)pyridine (50 mg, 0.41 mmol) in methylene chloride
(20 mL) was stirred overnight under an nitrogen atmosphere and
then filtered to remove solids. The filtrate was washed with water,
dried over anhydrous MgSO4, and concentrated in vacuo. The crude
material was purified by column chromatography on silica gel using
ethyl acetate-petroleum ether (3:1) as eluent to afford compound
6 (419 mg, 74.8%) as a colorless oil. 1H NMR (400 MHz, CDCl3)
δ 1.12-1.39 (m, 6H), 1.67-2.02 (m, 6H), 1.88 (s, 3H), 1.96 (s,
3H), 2.72 (t, 2H, J ) 7.8 Hz), 3.19 (m, 1H), 3.23 (dd, 1H, J ) 2.0,
12.3 Hz), 3.32 (dd, 1H, J ) 5.7, 12.3 Hz), 4.19 (m, 2H), 5.33 (dd,
1H, J ) 2.0, 5.7 Hz), 7.27 (m, 1H), 7.56 (d, 1H, J ) 7.9 Hz), 8.48
(s, 2H). FAB-MS [M + H]+ ) 419.2 m/e. EI-HRMS: calcd for
C22H31N2O4S [M + H]+, 419.2004; found, 419.1971. Anal.
(C22H30N2O4S): C, H, N.
3-Phenyl-1-propyl (2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-di-
oxoethyl)-2-(4-thiazolidine)carboxylate (7). This compound was
prepared from (2S)-5,5-dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-
2-(4-thiazolidine)carboxylic acid 5a (400 mg, 1.34 mmol) and
3-phenyl-1-propanol (274 mg, 2.01 mmol) in the same procedure
as described in the preparation of compound 6 (398 mg, 71.2%).
1H NMR (400 MHz, CDCl3) δ 1.10-1.37 (m, 6H), 1.63-1.97 (m,
6H), 1.88 (s, 3H), 1.95 (s, 3H), 2.69 (t, 2H, J ) 7.4 Hz), 3.19 (m,
1H), 3.24 (dd, 1H, J ) 1.5, 12.4 Hz), 3.33 (dd, 1H, J ) 5.8, 12.4
Hz), 4.19 (m, 2H), 5.02 (dd, 1H, J ) 1.5, 5.8 Hz), 7.20 (m, 3H),
7.31 (m, 2H). FAB-MS [M + H]+ ) 418.1 m/e. EI-HRMS:
2-[N-Ethyl-N-(3-methylphenyl)]amino-1-ethyl (2S)-5,5-Di-
methyl-1-(2-cyclohexyl-1,2-dioxoethyl)-2-(4-thiazolidine)carbox-
ylate (9). This compound was prepared from (2S)-5,5-dimethyl-
1-(2-cyclohexyl-1,2-dioxoethyl)-2-(4-thiazolidine)carboxylic acid 5a
(400 mg, 1.34 mmol) and 2-[N-ethyl-N-(3-methylphenyl)]amino-
1-ethanol (360 mg, 2.01 mmol) in the same procedure as described
in the preparation of compound 6 (454 mg, 73.7%). 1H NMR (400
MHz, CDCl3) δ 1.14-1.35 (m, 9H), 1.66-1.94 (m, 4H), 1.86 (s,
3H), 1.94 (s, 3H), 2.31 (s, 3H), 3.20 (m, 3H), 3.37 (m, 2H), 3.54
(m, 2H), 4.30 (m, 2H), 5.36 (m, 1H), 6.53 (m, 3H), 7.10 (m, 1H).
FAB-MS [M + H]+ ) 461.2 m/e. EI-HRMS: calcd for C25H36N2O4S
[M]+, 460.2396; found, 460.2396. Anal. (C25H36N2O4S): C, H, N.
9-Decen-1-yl (2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-dioxo-
ethyl)-2-(4-thiazolidine)carboxylate (10). This compound was
prepared from (2S)-5,5-dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-
2-(4-thiazolidine)carboxylic acid 5a (400 mg, 1.34 mmol) and
9-decen-1-ol (314 mg, 2.01 mmol) in the same procedure as
1
described in the preparation of compound 6 (370 mg, 63.1%). H
NMR (400 MHz, CDCl3) δ 1.08-2.12 (m, 25H), 1.83 (s, 3H), 1.87
(s, 3H), 3.16 (m, 2H), 4.16 (m, 2H), 4.93 (m, 1H), 4.99 (m, 1H),
5.37 (t, 1H, J ) 3.8 Hz), 5.80 (m, 1H). FAB-MS [M + H]+
)
438.2 m/e. EI-HRMS: calcd for C24H39NO4S [M]+, 437.2600;
found, 437.2537. Anal. (C24H39NO4S): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-(2-cyclopenyl-1,2-dioxoethyl)-2-(4-
thiazolidine)carboxylate (4b). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-
2-(4-thiazolidine)carboxylate 3 (1.0 g, 3.46 mmol) and a 2.0 M
solution of cyclopentylmagnesium chloride (2.3 mL, 4.6 mmol) in
ethyl ether in the same procedure as described in the preparation
of the intermediate compound 4a (850 mg, 78.5%).
(2S)-5,5-Dimethyl-1-(2-cyclohexyl-1,2-dioxoethyl)-2-(4-thiazoli-
dine)carboxylic Acid (5b). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(2-cyclopentyl-1,2-dioxo-
ethyl)-2-(4-thiazolidine)carboxylate 4b (850 mg, 2.72 mmol) in the
same procedure as described in the preparation of the intermediate
compound 5a (687 mg, 88.6%).
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(2-cyclopentyl-1,2-
dioxoethyl)-2-(4-thiazolidine)carboxylate (11). This compound
was prepared from (2S)-5,5-dimethyl-1-(2-cyclopentyl-1,2-dioxo-
ethyl)-2-(4-thiazolidine)carboxylic acid 5b (382 mg, 1.34 mmol)
and 3-(3-pyridyl)-1-propanol (275 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (379 mg,
1
70.1%). H NMR (400 MHz, CDCl3) δ 1.60-1.77 (m, 8H), 1.88
(s, 3H), 1.96 (s, 3H), 1.99 (m, 2H), 2.72 (t, 2H, J ) 8.0 Hz), 3.28
(dd, 1H, J ) 2.2, 12.3 Hz), 3.33 (dd, 1H, J ) 5.7, 12.3 Hz), 3.60
(m, 1H), 4.20 (m, 2H), 5.39 (dd, 1H, J ) 2.2, 5.7 Hz), 7.28 (m,
1H), 7.56 (d, 1H, J ) 7.8 Hz), 8.48 (s, 2H). FAB-MS [M + H]+
) 405.3 m/e. EI-HRMS: calcd for C21H29N2O4S [M + H]+,
405.1848; found, 405.1840. Anal. (C21H28N2O4S): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-dioxopentyl)-2-
(4-thiazolidine)carboxylate (4c). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-
2-(4-thiazolidine)carboxylate 3 (2.5 g, 8.65 mmol) and a 1.0 M
solution of 1,1-dimethylproplylmagnesium chloride (11.5 mL, 11.5
mmol) in ethyl ether in the same procedure as described in the
preparation of the intermediate compound 4a (1.99 g, 73.1%).

4066 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14
Zhao et al.
(2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-dioxopentyl)-2-(4-thia-
zolidine)carboxylic Acid (5c). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
pentyl)-2-(4-thiazolidine)carboxylate 4c (1.99 g, 6.32 mmol) in the
same procedure as described in the preparation of the intermediate
compound 5a (1.53 g, 84.1%).
J ) 6.3 Hz), 4.31 (m, 2H), 4.98 (d, 1H, J ) 5.9 Hz), 6.54 (m, 3H),
7.11 (m,1H). FAB-MS [M + H]+ ) 449.2 m/e. EI-HRMS:
calcd for C24H36N2O4S [M+], 448.2396; found, 448.2398. Anal.
(C24H36N2O4S): C, H, N.
2-(2-Thienyl)-1-ethyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-
dioxopentyl)-2-(4-thiazolidine)carboxylate (17). This compound
was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
pentyl)-2-(4-thiazolidine)carboxylic acid 5c (385 mg, 1.34 mmol)
and 2-(2-thienyl)-1-ethanol (257 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (373 mg,
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-
dioxopentyl)-2-(4-thiazolidine)carboxylate (12). This compound
was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
pentyl)-2-(4-thiazolidine)carboxylic acid 5c (385 mg, 1.34 mmol)
and 3-(3-pyridyl)-1-propanol (275 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (425 mg,
1
70.1%). H NMR (400 MHz, CDCl3) δ 0.82 (t, 3H, J ) 7.5 Hz),
1.17 (s, 3H), 1.27 (s,3H), 1.72 (m, 2H), 1.88 (s,3H), 1.94 (s,3H),
3.20 (m, 3H), 3.29 (dd, 1H, J ) 5.9, 12.2 Hz), 4.39 (m, 2H), 4.97
(dd, 1H, J ) 1.2, 5.9 Hz), 6.86 (d, 1H, J ) 3.3 Hz), 6.94 (dd, 1H,
J ) 3.4, 5.1 Hz), 7.17 (dd, 1H, J ) 1.1, 5.1 Hz). FAB-MS [M +
H]+ ) 398.0 m/e. EI-HRMS: calcd for C19H27NO4S2 [M+],
397.1382; found, 397.1423. Anal. (C19H27NO4S2): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-dioxobutyl)-2-(4-
thiazolidine)carboxylate (4d). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-
2-(4-thiazolidine)carboxylate 3 (2.5 g, 8.65 mmol) and a 2.0 M
solution of tert-butylmagnesium chloride (5.75 mL, 11.5 mmol) in
ethyl ether in the same procedure as described in the preparation
of the intermediate compound 4a (1.94 g, 74.7%).
1
78.2%). H NMR (600 MHz, CDCl3) δ 0.83 (t, 3H, J ) 7.2 Hz),
1.19 (s, 3H), 1.27 (s, 3H), 1.73 (q, 2H, J ) 7.2 Hz), 1.90 (s, 3H),
1.99 (s, 3H), 2.01 (m, 2H), 2.72 (t, 2H, J ) 7.8 Hz), 3.24 (d, 1H,
J ) 12.0 Hz), 3.32 (dd, 1H, J ) 6.0, 12.0 Hz), 4.23 (m, 2H), 4.93
(d, 1H, J ) 6.0 Hz), 7.23 (m, 1H), 7.52 (d, 1H, J ) 7.2 Hz), 8.47
(s, 2H). FAB-MS [M + H]+ ) 407.0 m/e. EI-HRMS: calcd for
C21H31N2O4S [M + H]+, 407.2004; found, 407.1957. Anal.
(C21H30N2O4S): C, H, N.
3-Phenyl-1-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-di-
oxopentyl)-2-(4-thiazolidine)carboxylate (13). This compound was
prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxopentyl)-
2-(4-thiazolidine)carboxylic acid 5c (385 mg, 1.34 mmol) and
3-phenyl-1-propanol (274 mg, 2.01 mmol) in the same procedure
as described in the preparation of compound 6 (387 mg, 71.4%).
1H NMR (400 MHz, CDCl3) δ 0.83 (t, 3H, J ) 7.5 Hz), 1.18 (s,
3H), 1.27 (s, 3H), 1.72 (m, 2H), 1.90 (s, 3H), 1.98 (s, 3H), 2.02
(m, 2H), 2.70 (t, 2H, J ) 7.6 Hz), 3.23 (dd, 1H, J ) 1.2, 12.2 Hz),
3.31 (dd, 1H, J ) 6.0, 12.2 Hz), 4.20 (m, 2H), 4.96 (dd, 1H, J )
1.2, 6.0 Hz), 7.17-7.31 (m, 5H). FAB-MS [M + H]+ ) 406.0
m/e. EI-HRMS: calcd for C22H31NO4S [M+], 405.1974; found,
405.1992. Anal. (C22H31NO4S): C, H, N.
(2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-dioxobutyl)-2-(4-thia-
zolidine)carboxylic Acid (5d). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
butyl)-2-(4-thiazolidine)carboxylate 4d (1.94 g, 6.45 mmol) in the
same procedure as described in the preparation of the intermediate
compound 5a (1.46 g, 83.1%).
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-
dioxobutyl)-2-(4-thiazolidine)carboxylate (18). This compound
was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
butyl)-2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34 mmol)
and 3-(3-pyridyl)-1-propanol (275 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (373 mg,
71.0%). 1H NMR (400 MHz, CDCl3) δ 1.29 (s, 9H), 1.91 (s, 3H),
1.98 (s, 3H), 2.01 (m, 2H), 2.72 (t, 2H, J ) 7.5 Hz), 3.26 (dd, 1H,
J ) 1.5, 12.2 Hz), 3.33 (dd, 1H, J ) 5.8, 12.2 Hz), 4.21 (m, 2H),
5.00 (dd, 1H, J ) 1.5, 5.8 Hz), 7.25 (m, 1H), 7.54 (m, 1H), 8.47
(m, 2H). FAB-MS [M + H]+ ) 393.4 m/e. EI-HRMS: calcd for
C20H29N2O4S [M + H]+, 393.1848; found, 393.1819. Anal.
(C20H28N2O4S): C, H, N.
3-Phenyl-1-prop-2-(E)-enyl (2S)-5,5-Dimethyl-1-(3,3-dimeth-
yl-1,2-dioxopentyl)-2-(4-thiazolidine)carboxylate (14). This com-
pound was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-
dioxopentyl)-2-(4-thiazolidine)carboxylic acid 5c (385 mg, 1.34
mmol) and 3-phenyl-1-prop-2-(E)-enol (269 mg, 2.01 mmol) in the
same procedure as described in the preparation of compound 6 (325
1
mg, 60.2%). H NMR (400 MHz, CDCl3) δ 0.81 (t, 3H, J ) 7.5
Hz), 1.17 (s, 3H), 1.28 (s, 3H), 1.71 (m, 2H), 1.90 (s, 3H), 1.97 (s,
3H), 3.33 (m, 2H), 4.82 (m, 2H), 5.07 (dd, 1H, J ) 2.7, 4.6 Hz),
6.25 (dt, 1H, J ) 6.5, 15.9 Hz), 6.68 (d, 1H, J ) 15.9 Hz), 7.26-
7.40 (m, 5H). FAB-MS [M + H]+ ) 404.3 m/e. EI-HRMS:
calcd for C22H29NO4S [M+], 403.1817; found, 403.1862. Anal.
(C22H29NO4S): C, H, N.
3-(6-Methyl-2-pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(3,3-di-
methyl-1,2-dioxobutyl)-2-(4-thiazolidine)carboxylate (19). This
compound was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-
1,2-dioxobutyl)-2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34
mmol) and 3-(6-methyl-2-pyridyl)-1-propanol (304 mg, 2.01 mmol)
in the same procedure as described in the preparation of compound
3-Phenoxy-1-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-
dioxopentyl)-2-(4-thiazolidine)carboxylate (15). This compound
was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
pentyl)-2-(4-thiazolidine)carboxylic acid 5c (385 mg, 1.34 mmol)
and 3-phenoxy-1-propanol (305 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (423 mg,
1
6 (360 mg, 66.2%). H NMR (400 MHz, CDCl3) δ 1.28 (s, 9H),
1.89 (s, 3H), 1.97 (s, 3H), 2.11 (m, 2H), 2.53 (s, 3H), 2.83 (t, 2H,
J ) 7.9 Hz), 3.27 (dd, 1H, J ) 1.9, 12.3 Hz), 3.32 (dd, 1H, J )
5.5, 12.3 Hz), 4.21 (m, 2H), 5.03 (dd, 1H, J ) 1.9, 5.5 Hz), 6.98
(m, 2H), 7.50 (t, 1H, J ) 7.7 Hz). FAB-MS [M + H]+ ) 407.2
m/e. EI-HRMS: calcd for C21H30N2O4S [M]+, 406.1926; found,
406.1915. Anal. (C21H30N2O4S): C, H, N.
1
74.9%). H NMR (400 MHz, CDCl3) δ 0.82 (t, 3H, J ) 7.5 Hz),
1.17 (s, 3H), 1.26 (s, 3H), 1.71 (m, 2H), 1.88 (s, 3H), 1.95 (s, 3H),
2.15 (m, 2H), 3.24 (dd, 1H, J ) 1.4, 12.2 Hz), 3.30 (dd, 1H, J )
5.8, 12.2 Hz), 4.05 (t, 2H, J ) 6.1 Hz), 4.40 (m, 2H), 4.93 (dd,
1H, J ) 1.4, 5.8 Hz), 6.90 (d, 2H, J ) 7.7 Hz), 6.95 (t, 1H, J )
7.4 Hz), 7.30 (m, 2H). FAB-MS [M + H]+ ) 422.1 m/e.
EI-HRMS: calcd for C22H31NO5S [M+], 421.1923; found, 421.1925.
Anal. (C22H31NO5S): C, H, N.
3-Phenyl-1-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-di-
oxobutyl)-2-(4-thiazolidine)carboxylate (20). This compound was
prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxobutyl)-
2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34 mmol) and
3-phenyl-1-propanol (274 mg, 2.01 mmol) in the same procedure
as described in the preparation of compound 6 (368 mg, 70.3%).
1H NMR (400 MHz, CDCl3) δ 1.28 (s, 9H), 1.90 (s, 3H), 1.97 (s,
3H), 2.00 (m, 2H), 2.69 (t, 2H, J ) 7.4 Hz), 3.24 (dd, 1H, J ) 1.4,
12.3 Hz), 3.31 (dd, 1H, J ) 5.8, 12.3 Hz), 4.19 (m, 2H), 5.02 (dd,
1H, J ) 1.4, 5.8 Hz), 7.19 (m, 3H), 7.29 (m, 2H). FAB-MS [M +
H]+ ) 392.4 m/e. EI-HRMS: calcd for C21H30NO4S [M + H]+,
392.1896; found, 392.1864. Anal. (C21H29NO4S): C, H, N.
1-Phenoxy-2-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-
dioxobutyl)-2-(4-thiazolidine)carboxylate (21). This compound
was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
2-[N-Ethyl-N-(3-methylphenyl)]amino-1-ethyl (2S)-5,5-Di-
methyl-1-(3,3-dimethyl-1,2-dioxopentyl)-2-(4-thiazolidine)car-
boxylate (16). This compound was prepared from (2S)-5,5-
dimethyl-1-(3,3-dimethyl-1,2-dioxopentyl)-2-(4-thiazolidine)carboxylic
acid 5c (385 mg, 1.34 mmol) and 2-[N-ethyl-N-(3-methylphenyl)]-
amino-1-ethanol (360 mg, 2.01 mmol) in the same procedure as
1
described in the preparation of compound 6 (403 mg, 67.2%). H
NMR (400 MHz, CDCl3) δ 0.82 (t, 3H, J ) 7.5 Hz), 1.13 (t, 3H,
J ) 7.0 Hz), 1.18 (s, 3H), 1.28 (s,3H), 1.73 (m, 2H), 1.88 (s,3H),
1.96 (s, 3H), 2.31 (s, 3H), 3.16-3.18 (d, 1H, J ) 12.2 Hz), 3.27
(dd, 1H, J ) 5.9, 12.2 Hz), 3.38 (q, 2H, J ) 7.0 Hz), 3.56 (t, 2H,

FK506-Binding Protein Ligands
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14 4067
butyl)-2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34 mmol)
and 1-phenoxy-2-propanol (305 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (402 mg,
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxooctyl)-
2-(4-thiazolidine)carboxylate (26). This compound was prepared
from (2S)-5,5-dimethyl-1-(1,2-dioxooctyl)-2-(4-thiazolidine)car-
boxylic acid 5e (403 mg, 1.34 mmol) and 3-(3-pyridyl)-1-propanol
(275 mg, 2.01 mmol) in the same procedure as described in the
preparation of compound 6 (423 mg, 75.1%). 1H NMR (400 MHz,
CDCl3) δ 0.87 (m, 3H), 1.28 (m, 6H), 1.54 (m, 2H), 1.87 (s, 3H),
1.97 (s, 3H), 2.00 (m, 2H), 2.71 (t, 2H, J ) 7.1 Hz), 2.73 (m, 1H),
2.99 (m, 1H), 3.31 (m, 2H), 4.19 (m, 2H), 5.42 (dd, 1H, J ) 2.8,
5.2 Hz), 7.26 (m, 1H), 7.54 (m, 1H), 8.48 (m, 2H). FAB-MS [M
+ H]+ ) 421.3 m/e. EI-HRMS: calcd for C22H32N2O4S [M]+,
420.2083; found, 420.2024. Anal. (C22H32N2O4S): C, H, N.
3-Phenyl-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxooctyl)-2-(4-
thiazolidine)carboxylate (27). This compound was prepared from
(2S)-5,5-dimethyl-1-(1,2-dioxooctyl)-2-(4-thiazolidine)carboxylic acid
5e (403 mg, 1.34 mmol) and 3-phenyl-1-propanol (274 mg, 2.01
mmol) in the same procedure as described in the preparation of
compound 6 (399 mg, 71.0%). 1H NMR (400 MHz, CDCl3) δ 0.87
(m, 3H), 1.27 (m, 6H), 1.54 (m, 2H), 1.86 (s, 3H), 1.93 (s, 3H),
1.98 (m, 2H), 2.69 (t, 2H, J ) 7.4 Hz), 2.70 (m, 1H), 2.99 (m,
1H), 3.30 (m, 2H), 4.17 (m, 2H), 5.43 (dd, 1H, J ) 3.3, 4.5 Hz),
7.19 (m, 3H), 7.29 (m, 2H). FAB-MS [M + H]+ ) 420.1 m/e.
EI-HRMS: calcd for C23H33NO4S [M]+, 419.2130; found, 419.2145.
Anal. (C23H33NO4S): C, H, N.
3-Phenyl-1-prop-2-(E)-enyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-
octyl)-2-(4-thiazolidine)carboxylate (28). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxooctyl)-2-(4-thiazoli-
dine)carboxylic acid 5e (403 mg, 1.34 mmol) and 3-phenyl-1-prop-
2-(E)-enol (269 mg, 2.01 mmol) in the same procedure as described
in the preparation of compound 6 (330 mg, 59.1%). 1H NMR (400
MHz, CDCl3) δ 0.87 (m, 3H), 1.27 (m, 6H), 1.53 (m, 2H), 1.86 (s,
3H), 1.93 (s, 3H), 2.72 (m, 1H), 3.02 (m, 1H), 3.33 (dd, 1H, J )
5.8, 12.2 Hz), 3.38 (dd, 1H, J ) 2.2, 12.2 Hz), 4.80 (m, 2H), 5.50
(dd, 1H, J ) 2.2, 5.8 Hz), 6.23 (dt, 1H, J ) 6.4, 15.9 Hz), 6.66 (d,
1H, J ) 15.9 Hz), 7.33 (m, 5H). FAB-MS [M + H]+ )418.1 m/e.
EI-HRMS: calcd for C23H32NO4S [M + H]+, 418.2052; found,
418.2047. Anal. (C23H31NO4S): C, H, N.
2-(2-Chlorophenyl)-1-ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-
octyl)-2-(4-thiazolidine)carboxylate (29). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxooctyl)-2-(4-thia-
zolidine)carboxylic acid 5e (403 mg, 1.34 mmol) and 2-(2-
chlorophenyl)-1-ethanol (314 mg, 2.01 mmol) in the same procedure
as described in the preparation of compound 6 (398 mg, 67.6%).
1H NMR (400 MHz, CDCl3) δ 0.87 (m, 3H), 1.29 (m, 6H), 1.53
(m, 2H), 1.84 (s, 3H), 1.89 (s, 3H), 2.66 (m, 1H), 2.98 (m, 1H),
3.09 (t, 2H, J ) 6.8 Hz), 3.26 (m, 2H), 4.40 (t, 2H, J ) 6.8 Hz),
5.40 (dd, 1H, J ) 3.2, 4.9 Hz), 7.21 (m, 3H), 7.37 (m, 1H). FAB-
MS [M + H]+ ) 440.0 m/e. EI-HRMS: calcd for C22H30ClNO4S
[M]+, 439.1584; found, 439.1554. Anal. (C22H30ClNO4S): C, H,
N.
Ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazolidine)-
carboxylate (4f). This intermediate compound was prepared from
ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-2-(4-thiazoli-
dine)carboxylate 3 (2.5 g, 8.65 mmol) and a 2.0 M solution of
octylmagnesium chloride (5.75 mL, 11.5 mmol) in THF in the same
procedure as described in the preparation of the intermediate
compound 4a (2.16 g, 69.8%).
1
73.7%). H NMR (400 MHz, CDCl3) δ 1.27 (d, 3H, J ) 2.3 Hz),
1.28 (s, 9H), 1.88 (s, 3H), 1.94 (s, 3H), 3.29 (m, 2H), 4.30 (m,
2H), 5.01 (m, 1H), 5.31 (m, 1H), 6.93 (m, 3H), 7.28 (m, 2H). FAB-
MS [M + H]+ ) 408.3 m/e. EI-HRMS: calcd for C21H29NO5S
[M]+, 407.1766; found, 407.1789. Anal. (C21H29NO5S): C, H, N.
3-Cyclohexyl-1-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-
dioxobutyl)-2-(4-thiazolidine)carboxylate (22). This compound
was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxo-
butyl)-2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34 mmol)
and 3-cyclohexyl-1-propanol (285 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (370 mg,
1
69.5%). H NMR (400 MHz, CDCl3) δ 0.87 (m, 2H), 1.11-1.26
(m, 6H), 1.28 (s, 9H), 1.62-1.70 (m, 7H), 1.89 (s, 3H), 1.95 (s,
3H), 3.28 (dd, 1H, J ) 2.1, 12.2 Hz), 3.32 (dd, 1H, J ) 5.4, 12.2
Hz), 4.14 (m, 2H), 5.04 (dd, 1H, J ) 2.1, 5.4 Hz). FAB-MS [M +
H]+ ) 398.3 m/e. EI-HRMS: calcd for C21H36NO4S [M + H]+,
398.2365; found, 398.2342. Anal. (C21H35NO4S): C, H, N.
3-(N,N-Dibenzylamino)-1-propyl (2S)-5,5-Dimethyl-1-(3,3-di-
methyl-1,2-dioxobutyl)-2-(4-thiazolidine)carboxylate (23). This
compound was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-
1,2-dioxobutyl)-2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34
mmol) and 3-(N,N-dibenzylamino)-1-propanol (513 mg, 2.01 mmol)
in the same procedure as described in the preparation of compound
1
6 (387 mg, 56.7%). H NMR (400 MHz, CDCl3) δ 1.27 (s, 9H),
1.82 (m, 2H), 1.86 (s, 3H), 1.90 (s, 3H), 2.49 (t, 2H, J ) 6.7 Hz),
2.93 (d, 1H, J ) 12.3 Hz), 3.14 (dd, 1H, J ) 6.0, 12.3 Hz), 3.54
(s, 4H), 4.19 (m, 2H), 4.92 (d, 1H, J ) 6.0 Hz), 7.22-7.35 (m,
10H). FAB-MS [M + H]+ ) 511.3 m/e. EI-HRMS: calcd for
C29H38N2O4S [M]+, 510.2552; found, 510.2543. Anal. (C29H38N2O4S):
C, H, N.
9-Decen-1-yl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-1,2-dioxo-
butyl)-2-(4-thiazolidine)carboxylate (24). This compound was
prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-dioxobutyl)-
2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34 mmol) and
9-decen-1-ol (314 mg, 2.01 mmol) in the same procedure as
1
described in the preparation of compound 6 (323 mg, 58.6%). H
NMR (400 MHz, CDCl3) δ 1.28 (s, 9H), 1.28-1.37 (m, 10H), 1.64
(m, 2H), 1.89 (s, 3H), 1.96 (s, 3H), 2.04 (m, 2H), 3.28 (dd, 1H, J
) 2.1, 12.2 Hz), 3.32 (dd, 1H, J ) 5.4, 12.2 Hz), 4.15 (m, 2H),
4.93 (dd, 1H, J ) 2.0, 12.2 Hz), 4.99 (dd, 1H, J ) 2.0, 15.5 Hz),
5.04 (dd, 1H, J ) 2.1, 5.4 Hz), 5.79 (ddt, 1H, J ) 6.7, 12.2, 15.5
Hz). FAB-MS [M + H]+ ) 412.4 m/e. EI-HRMS: calcd for
C22H38NO4S [M + H]+, 412.2522; found, 412.2522. Anal.
(C22H37NO4S): C, H, N.
(2R)-1-Methoxy-2-propyl (2S)-5,5-Dimethyl-1-(3,3-dimethyl-
1,2-dioxobutyl)-2-(4-thiazolidine)carboxylate (25). This com-
pound was prepared from (2S)-5,5-dimethyl-1-(3,3-dimethyl-1,2-
dioxobutyl)-2-(4-thiazolidine)carboxylic acid 5d (366 mg, 1.34
mmol) and (2R)-1-methoxy-2-propanol (181 mg, 2.01 mmol) in
the same procedure as described in the preparation of compound 6
1
(332 mg, 71.8%). H NMR (400 MHz, CDCl3) δ 1.27 (m, 12H),
1.89 (s, 3H), 1.96 (s, 3H), 3.30 (m, 2H), 3.34 (s, 3H), 3.43 (m,
2H), 5.02 (dd, 1H, J ) 2.5, 4.9 Hz), 5.13 (m, 1H). FAB-MS [M +
H]+ ) 346.1 m/e. EI-HRMS: calcd for C16H28NO5S [M + H]+,
346.1688; found, 346.1654. Anal. (C16H27NO5S): C, H, N.
(2S)-5,5-Dimethyl-1-(1,2-dioxoodecyl)-2-(4-thiazolidine)car-
boxylic Acid (5f). This intermediate compound was prepared from
ethyl (2S)-5,5-dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazolidine)car-
boxylate 4f (2.16 g, 6.05 mmol) in the same procedure as described
in the preparation of the intermediate compound 5a (1.53 g, 76.9%).
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxodecyl)-
2-(4-thiazolidine)carboxylate (30). This compound was prepared
from (2S)-5,5-dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazolidine)car-
boxylic acid 5f (441 mg, 1.34 mmol) and 3-(3-pyridyl)-1-propanol
(275 mg, 2.01 mmol) in the same procedure as described in the
preparation of compound 6 (467 mg, 77.8%). 1H NMR (600 MHz,
CDCl3) δ 0.87 (t, 3H, J ) 7.2 Hz), 1.29 (m, 10H), 1.55 (m, 2H),
1.87 (s, 3H), 1.94 (s, 3H), 2.01 (m, 2H), 2.70 (t, 2H, J ) 7.8 Hz),
2.74 (m, 1H), 3.01 (m, 1H), 3.32 (m, 2H), 4.20 (m, 2H), 5.43 (dd,
Ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxooctyl)-2-(4-thiazolidine)-
carboxylate (4e). This intermediate compound was prepared from
ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-2-(4-thiazoli-
dine)carboxylate 3 (2.5 g, 8.65 mmol) and a 2.0 M solution of
hexylmagnesium chloride (5.75 mL, 11.5 mmol) in THF in the same
procedure as described in the preparation of the intermediate
compound 4a (2.01 g, 70.7%).
(2S)-5,5-Dimethyl-1-(1,2-dioxooctyl)-2-(4-thiazolidine)carbox-
ylic Acid (5e). This intermediate compound was prepared from
ethyl (2S)-5,5-dimethyl-1-(1,2-dioxooctyl)-2-(4-thiazolidine)car-
boxylate 4e (2.01 g, 6.11 mmol) in the same procedure as described
in the preparation of the intermediate compound 5a (1.49 g, 81.0%).

4068 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14
Zhao et al.
1H, J ) 2.4, 5.4 Hz), 7.25 (m, 1H), 7.53 (d, 1H, J ) 7.8 Hz), 8.48
(s, 2H). FAB-MS [M + H]+ )449.2 m/e. EI-HRMS: calcd for
C24H36N2O4S [M]+, 448.2396; found, 448.2405. Anal. (C24H36N2O4S):
C, H, N.
in the preparation of compound 6 (411 mg, 74.7%). 1H NMR (400
MHz, CDCl3) δ 1.80 (m, 2H), 1.99 (s, 3H), 2.09 (s, 3H), 2.56 (m,
2H), 3.30 (dd, 1H, J ) 1.4, 12.1 Hz), 3.38 (dd, 1H, J ) 5.8, 12.1
Hz), 3.93 (dt, 1H, J ) 6.5, 10.9 Hz), 4.05 (dt, 1H, J ) 6.5, 10.9
Hz), 5.20 (dd, 1H, J ) 1.4, 5.8 Hz), 7.09-8.03 (m, 10H). FAB-
MS [M + H]+ ) 412.4 m/e. EI-HRMS: calcd for C23H25NO4S
[M]+, 411.1504; found, 411.1492. Anal. (C23H25NO4S): C, H, N.
3-Phenyl-1-prop-2-(E)-enyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-
phenyl)ethyl-2-(4-thiazolidine)carboxylate (36). This compound
was prepared from (2S)-5,5-dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-
2-(4-thiazolidine)carboxylic acid 5g (393 mg, 1.34 mmol) and
3-phenyl-1-prop-2-(E)-enol (269 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (335 mg,
61.1%). 1H NMR (400 MHz, CDCl3) δ 1.98 (s, 3H), 2.09 (s, 3H),
3.39 (d, 2H, J ) 3.9 Hz), 4.54 (ddd, 1H, J ) 1.2, 6.6, 12.7 Hz),
4.64 (m, 1H), 5.28 (t, 1H, J ) 3.9 Hz), 5.99 (dt, 1H, J ) 6.6, 15.9
Hz), 6.49 (d, 1H, J ) 15.9 Hz), 7.26-8.03 (m, 10H). FAB-MS [M
+ H]+ ) 410.4 m/e. EI-HRMS: calcd for C23H23NO4S [M]+,
409.1348; found, 409.1372. Anal. (C23H23NO4S): C, H, N.
2-(2-Chlorophenyl)-1-ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-
decyl)-2-(4-thiazolidine)carboxylate (31). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazoli-
dine)carboxylic acid 5f (441 mg, 1.34 mmol) and 2-(2-chloro-
phenyl)-1-ethanol (314 mg, 2.01 mmol) in the same procedure as
1
described in the preparation of compound 6 (422 mg, 67.5%). H
NMR (600 MHz, CDCl3) δ 0.87 (t, 3H, J ) 7.2 Hz), 1.27 (m,
10H), 1.53 (m, 2H), 1.84 (s, 3H), 1.89 (s, 3H), 2.67 (m, 1H), 2.98
(m, 1H), 3.09 (t, 2H, J ) 6.6 Hz), 3.28 (m, 2H), 4.39 (t, 2H, J )
6.6 Hz), 5.40 (dd, 1H, J ) 3.6, 6.0 Hz), 7.20 (m, 3H), 7.36 (m,
1H). FAB-MS [M + H]+ ) 468.3 m/e. EI-HRMS: calcd for
C24H35ClNO4S [M + H]+, 468.1975; found, 468.1982. Anal.
(C24H34ClNO4S): C, H, N.
(2R)-1-Methoxy-2-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-
decyl)-2-(4-thiazolidine)carboxylate (32). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazoli-
dine)carboxylic acid 5f (441 mg, 1.34 mmol) and (2R)-1-methoxy-
2-propanol (181 mg, 2.01 mmol) in the same procedure as described
in the preparation of compound 6 (300 mg, 55.8%). 1H NMR (600
MHz, CDCl3) δ 0.87 (t, 3H, J ) 7.2 Hz), 1.23 (m, 13H), 1.55 (m,
2H), 1.86 (s, 3H), 1.92 (s, 3H), 2.70 (m,1H), 3.03 (m, 1H), 3.29
(m, 2H), 3.35 (s, 3H), 3.41 (m, 2H), 5.10 (m, 1H), 5.43 (m, 1H).
FAB-MS [M + H]+ ) 402.1 m/e. EI-HRMS: calcd for C20H36NO5S
[M + H]+, 402.2314; found, 402.2316. Anal. (C20H35NO5S): C,
H, N.
2-Pentyl (2S)-5,5-Dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazoli-
dine)carboxylate (33). This compound was prepared from (2S)-
5,5-dimethyl-1-(1,2-dioxodecyl)-2-(4-thiazolidine)carboxylic acid
5f (441 mg, 1.34 mmol) and 2-pentanol (177 mg, 2.01 mmol) in
the same procedure as described in the preparation of compound 6
(321 mg, 60.1%). 1H NMR (600 MHz, CDCl3) δ 0.87 (t, 3H, J )
7.2 Hz), 0.91 (m, 3H), 1.21 (t, 3H, J ) 7.8 Hz), 1.26-1.38 (m,
12H), 1.44-1.61 (m, 4H), 1.86 (s, 3H), 1.92 (s, 3H), 2.71 (m, 1H),
3.03 (m, 1H), 3.31 (m, 2H), 4.95 (m, 1H), 5.41 (m, 1H). FAB-MS
[M + H]+ ) 400.1 m/e. EI-HRMS: calcd for C21H38NO4S [M +
H]+, 400.2522; found, 400.2504. Anal. (C21H37NO4S): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-2-(4-thia-
zolidine)carboxylate (4g). This intermediate compound was pre-
pared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxyethyl)-2-
(4-thiazolidine)carboxylate 3 (2.5 g, 8.65 mmol) and a 2.0 M
solution of phenylmagnesium chloride (5.75 mL, 11.5 mmol) in
THF in the same procedure as described in the preparation of the
intermediate compound 4a (2.1 g, 75.6%).
3-Cyclohexyl-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-pheny)-
ethyl-2-(4-thiazolidine)carboxylate (37). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-2-(4-
thiazolidine)carboxylic acid 5g (393 mg, 1.34 mmol) and 3-cyclo-
hexyl-1-propanol (285 mg, 2.01 mmol) in the same procedure as
1
described in the preparation of compound 6 (397 mg, 71.0%). H
NMR (400 MHz, CDCl3) δ 0.79-1.82 (m, 15H), 1.98 (s, 3H), 2.08
(s, 3H), 3.34 (dd, 1H, J ) 1.9, 12.2 Hz), 3.38 (dd, 1H, J ) 5.4,
12.2 Hz), 3.85 (dt, 1H, J ) 6.9, 10.6 Hz), 3.98 (dt, 1H, J ) 6.9,
10.6 Hz), 5.22 (dd, 1H, J ) 1.9, 5.4 Hz), 7.42-8.08 (m, 5H). FAB-
MS [M + H]+ ) 418.4 m/e. EI-HRMS: calcd for C23H32NO4S
[M + H]+, 418.2052; found, 418.2047. Anal. (C23H31NO4S): C,
H, N.
9-Decen-1-yl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-
2-(4-thiazolidine)carboxylate (38). This compound was prepared
from (2S)-5,5-dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-2-(4-thiazoli-
dine)carboxylic acid 5g (393 mg, 1.34 mmol) and 9-decen-1-ol (314
mg, 2.01 mmol) in the same procedure as described in the
preparation of compound 6 (336 mg, 58.2%). 1H NMR (400 MHz,
CDCl3) δ 1.20-1.44 (m, 12H), 1.98 (s, 3H), 2.03 (m, 2H), 2.07 (s,
3H), 3.33 (dd, 1H, J ) 1.9, 12.1 Hz), 3.38 (dd, 1H, J ) 5.4, 12.1
Hz), 3.87 (dt, 1H, J ) 6.8, 10.7 Hz), 3.99 (dt, 1H, J ) 6.8, 10.7
Hz), 4.97 (m, 2H), 5.22 (dd, 1H, J ) 1.9, 5.4 Hz), 5.79 (m, 1H),
7.47 (m, 2H), 7.61 (m, 1H), 8.02 (m, 2H). FAB-MS [M + H]+
)
432.4 m/e. EI-HRMS: calcd for C24H33NO4S [M]+, 431.2130;
found, 431.2130. Anal. (C24H33NO4S): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-[2-(4-chlorophenyl)-1,2-dioxoethyl]-
2-(4-thiazolidine)carboxylate (4h). This intermediate compound
was prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxy-
ethyl)-2-(4-thiazolidine)carboxylate 3 (1.0 g, 3.46 mmol) and a 1.0
M solution of 4-chlorophenylmagnesium bromide (4.6 mL, 4.6
mmol) in ethyl ether in the same procedure as described in the
preparation of the intermediate compound 4a (829 mg, 67.3%).
(2S)-5,5-Dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-2-(4-thiazoli-
dine)carboxylic Acid (5g). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-
2-(4-thiazolidine)carboxylate 4g (2.1 g, 6.54 mmol) in the same
procedure as described in the preparation of the intermediate
compound 5a (1.49 g, 77.8%).
(2S)-5,5-Dimethyl-1-[2-(4-chlorophenyl)-1,2-dioxoethyl]-2-(4-
thiazolidine)carboxylic Acid (5h). This intermediate compound
was prepared from ethyl (2S)-5,5-dimethyl-1-[2-(4-chlorophenyl)-
1,2-dioxoethyl]-2-(4-thiazolidine)carboxylate 4h (829 mg, 2.33
mmol) in the same procedure as described in the preparation of
the intermediate compound 5a (682 g, 89.2%).
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-phenyl)-
ethyl-2-(4-thiazolidine)carboxylate (34). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-2-(4-
thiazolidine)carboxylic acid 5g (393 mg, 1.34 mmol) and 3-(3-
pyridyl)-1-propanol (275 mg, 2.01 mmol) in the same procedure
as described in the preparation of compound 6 (441 mg, 79.9%).
1H NMR (400 MHz, CDCl3) δ 1.80 (m, 2H), 1.99 (s, 3H), 2.09 (s,
3H), 2.57 (m, 2H), 3.31 (dd, 1H, J ) 1.5, 12.2 Hz), 3.39 (dd, 1H,
J ) 5.8, 12.2 Hz), 3.98 (dt, 1H, J ) 6.4, 10.9 Hz), 4.07 (dt, 1H, J
) 6.4, 10.9 Hz), 5.20 (dd, 1H, J ) 1.5, 5.8 Hz), 7.22 (m, 1H),
7.42-7.60 (m, 5H), 8.01 (m, 1H); 8.45 (m, 2H). FAB-MS [M +
H]+ ) 413.3 m/e. EI-HRMS: calcd for C22H24N2O4S [M]+,
412.1457; found, 412.1450. Anal. (C22H24N2O4S): C, H, N.
3-Phenyl-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-2-phenyl)-
ethyl-2-(4-thiazolidine)carboxylate (35). This compound was
prepared from (2S)-5,5-dimethyl-1-(1,2-dioxo-2-phenyl)ethyl-2-(4-
thiazolidine)carboxylic acid 5g (393 mg, 1.34 mmol) and 3-phenyl-
1-propanol (274 mg, 2.01 mmol) in the same procedure as described
3-(3-Pyridyl)-1-propyl
(2S)-5,5-Dimethyl-1-[2-(4-chloro-
phenyl)-1,2-dioxoethyl]-2-(4-thiazolidine)carboxylate (39). This
compound was prepared from (2S)-5,5-dimethyl-1-[2-(4-chloro-
phenyl)-1,2-dioxoethyl]-2-(4-thiazolidine)carboxylic acid 5h (438
mg, 1.34 mmol) and 3-(3-pyridyl)-1-propanol (275 mg, 2.01 mmol)
in the same procedure as described in the preparation of compound
1
6 (456 mg, 76.3%). H NMR (600 MHz, CDCl3) δ 1.83 (m, 2H),
1.97 (s, 3H), 2.07 (s, 3H), 2.58 (m, 2H), 3.36 (m, 2H), 4.07 (m,
2H), 5.26 (m, 1H), 7.23 (m, 1H), 7.49 (m, 3H), 7.99 (m, 2H,),
8.45 (m, 2H). FAB-MS [M + H]+ ) 447.2 m/e. EI-HRMS: calcd
for C22H23ClN2O4S [M]+, 446.1067; found, 446.1069. Anal.
(C22H23ClN2O4S): C, H, N.

FK506-Binding Protein Ligands
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14 4069
Ethyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-trimethylphenyl)]-
ethyl-2-(4-thiazolidine)carboxylate (4i). This intermediate com-
pound was prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-
ethoxyethyl)-2-(4-thiazolidine)carboxylate 3 (2.5 g, 8.65 mmol) and
a 1.0 M solution of 2,4,6-trimethylphenylmagnesium bromide (11.5
mL, 11.5 mmol) in THF in the same procedure as described in the
preparation of the intermediate compound 4a (2.23 g, 71.0%).
(2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-trimethylphenyl)]ethyl-
2-(4-thiazolidine)carboxylic Acid (5i). This intermediate com-
pound was prepared from ethyl (2S)-5,5-dimethyl-1-[1,2-dioxo-2-
(2,4,6-trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylate 4i (2.23
g, 6.14 mmol) in the same procedure as described in the preparation
of the intermediate compound 5a (1.67 mg, 81.2%).
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-
trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylate (40). This
compound was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-
(2,4,6-trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i
(449 mg, 1.34 mmol) and 3-(3-pyridyl)-1-propanol (275 mg, 2.01
mmol) in the same procedure as described in the preparation of
compound 6 (386 mg, 63.5%). 1H NMR (400 MHz, CDCl3) δ 1.92
(s, 3H), 2.03 (s, 3H), 2.04 (m, 2H), 2.25 (s, 6H), 2.28 (s, 3H), 2.75
(t, 2H, J ) 7.7 Hz), 3.31 (dd, 1H, J ) 1.2, 12.3 Hz), 3.39 (dd, 1H,
J ) 6.0, 12.3 Hz), 4.28 (m, 2H), 5.36 (dd, 1H, J ) 1.2, 6.0 Hz),
6.85 (s, 2H), 7.22 (m, 1H), 7.55 (m, 1H), 8.48 (m, 2H). FAB-MS
[M + H]+ ) 455.1 m/e. EI-HRMS: calcd for C25H30N2O4S [M]+,
454.1926; found, 454.1909. Anal. (C25H30N2O4S): C, H, N.
3-Phenyl-1-propyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-tri-
methylphenyl)]ethyl-2-(4-thiazolidine)carboxylate (41). This com-
pound was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-(2,4,6-
trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i (449 mg,
1.34 mmol) and 3-phenyl-1-propanol (274 mg, 2.01 mmol) in the
same procedure as described in the preparation of compound 6 (416
mg, 68.6%). 1H NMR (400 MHz, CDCl3) δ 1.92 (s, 3H), 2.02 (m,
2H), 2.03 (s, 3H), 2.25 (s, 6H), 2.28 (s, 3H), 2.73 (t, 2H, J ) 7.5
Hz), 3.30 (dd, 1H, J ) 1.2, 12.2 Hz), 3.37 (dd, 1H, J ) 6.1, 12.2
Hz), 4.25 (m, 2H), 5.37 (dd, 1H, J ) 1.2, 6.1 Hz), 6.85 (s, 2H),
7.20 (m, 3H), 7.28 (m, 2H). FAB-MS [M + H]+ ) 454.2 m/e.
EI-HRMS: calcd for C26H32NO4S [M + H]+, 454.2052; found,
454.2038. Anal. (C26H31NO4S): C, H, N.
3-Cyclohexyl-1-propyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-
trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylate (42). This
compound was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-
(2,4,6-trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i
(449 mg, 1.34 mmol) and 3-cyclohexyl-1-propanol (285 mg, 2.01
mmol) in the same procedure as described in the preparation of
compound 6 (361 mg, 58.7%). 1H NMR (400 MHz, CDCl3) δ 0.87
(m, 2H), 1.11-1.28 (m, 6H), 1.60-1.70 (m, 7H), 1.91 (s, 3H),
2.01 (s, 3H), 2.25 (s, 6H), 2.28 (s, 3H), 3.32 (dd, 1H, J ) 1.7, 12.2
Hz), 3.37 (dd, 1H, J ) 5.6, 12.2 Hz), 4.20 (m, 2H), 5.38 (dd, 1H,
J ) 1.7, 5.6 Hz), 6.85 (s, 2H). FAB-MS [M + H]+ ) 460.2 m/e.
EI-HRMS: calcd for C26H38NO4S [M + H]+, 460.2522; found,
460.2495. Anal. (C26H37NO4S): C, H, N.
3-Phenoxy-1-propyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-
trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylate (43). This
compound was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-
(2,4,6-trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i
(449 mg, 1.34 mmol) and 3-phenoxy-1-propanol (305 mg, 2.01
mmol) in the same procedure as described in the preparation of
compound 6 (378 mg, 60.1%). 1H NMR (400 MHz, CDCl3) δ 1.90
(s, 3H), 1.99 (s, 3H), 2.19 (m, 2H), 2.23 (s, 6H), 2.28 (s, 3H), 3.30
(dd, 1H, J ) 1.3, 12.3 Hz), 3.36 (dd, 1H, J ) 5.8, 12.3 Hz), 4.08
(m, 2H), 4.45 (m, 2H), 5.35 (dd, 1H, J ) 1.3, 5.8 Hz), 6.84 (s,
2H), 6.94 (m, 3H), 7.26 (m, 2H). FAB-MS [M + H]+ ) 470.1
m/e. EI-HRMS: calcd for C26H32NO5S [M + H]+, 470.2001; found,
470.2077. Anal. (C26H31NO5S): C, H, N.
(281 mg, 47.6%). 1H NMR (400 MHz, CDCl3) δ 1.89 (s, 3H), 1.96
(s, 3H), 2.22 (s, 6H), 2.28 (s, 3H), 3.31 (dd, 1H, J ) 1.5, 12.4 Hz),
3.36 (dd, 1H, J ) 5.8, 12.4 Hz), 3.48-5.05 (br, 2H), 5.23 (m, 2H),
5.29 (dd, 1H, J ) 1.5, 5.8 Hz), 6.74 (m, 2H), 6.84 (s, 2H), 7.17
(m, 2H). FAB-MS [M + H]+ ) 441.1 m/e. EI-HRMS: calcd for
C24H28N2O4S [M]+, 440.1770; found, 440.1751. Anal. (C24H28N2O4S):
C, H, N.
2-(N-Benzyl-N-methyl)amino-1-ethyl (2S)-5,5-Dimethyl-1-
[1,2-dioxo-2-(2,4,6-trimethylphenyl)]ethyl-2-(4-thiazolidine)car-
boxylate (45). This compound was prepared from (2S)-5,5-
dimethyl-1-[1,2-dioxo-2-(2,4,6-trimethylphenyl)]ethyl-2-(4-
thiazolidine)carboxylic acid 5i (449 mg, 1.34 mmol) and 2-(N-
benzyl-N-methyl)amino-1-ethanol (332 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (353 mg,
54.7%). 1H NMR (400 MHz, CDCl3) δ 1.91 (s, 3H), 2.01 (s, 3H),
2.24 (s, 6H), 2.28 (s, 6H), 2.77 (m, 2H), 3.30 (dd, 1H, J ) 1.5,
12.3 Hz), 3.36 (dd, 1H, J ) 5.8, 12.3 Hz), 3.58 (m, 2H), 4.37 (m,
2H), 5.38 (dd, 1H, J ) 1.5, 5.8 Hz), 6.84 (s, 2H); 7.25 (m, 1H),
7.30 (m, 4H). FAB-MS [M + H]+ ) 483.2 m/e. EI-HRMS: calcd
for C27H35N2O4S [M + H]+, 483.2318; found, 483.2370. Anal.
(C27H34N2O4S): C, H, N.
1-Phenoxy-2-propyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-
trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylate (46). This
compound was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-
(2,4,6-trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i
(449 mg, 1.34 mmol) and 1-phenoxy-2-propanol (305 mg, 2.01
mmol) in the same procedure as described in the preparation of
compound 6 (424 mg, 67.4%). 1H NMR (400 MHz, CDCl3) δ1.32
(m, 3H), 1.90 (s, 3H), 2.04 (s, 3H), 2.25 (s, 6H), 2.28 (s, 3H), 3.28
(dd, 1H, J ) 3.5, 12.7 Hz), 3.42 (dd, 1H, J ) 6.8, 12.7 Hz), 3.67
(m, 2H), 4.16 (m, 1H), 5.45 (dd, 1H, J ) 3.5, 6.8 Hz), 6.89 (m,
5H), 7.26 (m, 2H). FAB-MS [M + H]+ ) 470.1 m/e. EI-HRMS:
calcd for C26H31NO5S [M]+, 469.1923; found, 469.1923. Anal.
(C26H31NO5S): C, H, N.
9-Decen-1-yl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-trimethyl-
phenyl)]ethyl-2-(4-thiazolidine)carboxylate (47). This compound
was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-(2,4,6-tri-
methylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i (449 mg,
1.34 mmol) and 9-decen-1-ol (314 mg, 2.01 mmol) in the same
procedure as described in the preparation of compound 6 (321 mg,
50.6%). 1H NMR (400 MHz, CDCl3) δ 1.28-1.38 (m, 10H), 1.67
(m, 2H), 1.91 (s, 3H), 2.01 (s, 3H), 2.02 (m, 2H), 2.25 (s, 6H),
2.28 (s, 3H), 3.32 (dd, 1H, J ) 1.6, 12.3 Hz), 3.37 (dd, 1H, J )
5.7, 12.3 Hz), 4.22 (m, 2H), 4.93 (dd, 1H, J ) 1.8, 10.2 Hz), 4.99
(dd, 1H, J ) 1.8, 17.1 Hz), 5.38 (dd, 1H, J ) 1.6, 5.7 Hz), 5.80
(ddt, 1H, J ) 6.7, 10.2, 17.1 Hz), 6.85 (s, 2H). FAB-MS [M +
H]+ ) 474.2 m/e. EI-HRMS: calcd for C27H40NO4S [M + H]+,
474.2678; found, 474.2708. Anal. (C27H39NO4S): C, H, N.
Ethyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-4-methyl-4-phenyl)pen-
tyl-2-(4-thiazolidine)carboxylate (4j). This intermediate compound
was prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-2-ethoxy-
ethyl)-2-(4-thiazolidine)carboxylate 3 (1.5 g, 5.19 mmol) and a 0.5
M solution of 2-methyl-2-phenylproplymagnesium chloride (13.8
mL, 6.9 mmol) in ethyl ether in the same procedure as described
in the preparation of the intermediate compound 4a (1.27 g, 64.7%).
(2S)-5,5-Dimethyl-1-(1,2-dioxo-4-methyl-4-phenyl)pentyl-2-(4-
thiazolidine)carboxylic Acid (5j). This intermediate compound was
prepared from ethyl (2S)-5,5-dimethyl-1-(1,2-dioxo-4-methyl-4-
phenyl)pentyl-2-(4-thiazolidine)carboxylate 4j (1.27 g, 3.34 mmol)
in the same procedure as described in the preparation of the
intermediate compound 5a (894 mg, 76.7%).
3-(3-Pyridyl)-1-propyl (2S)-5,5-Dimethyl-1-(1,2-dioxo-4-meth-
yl-4-phenyl)pentyl-2-(4-thiazolidine)carboxylate (48). This com-
pound was prepared from (2S)-5,5-dimethyl-1-(1,2-dioxo-4-methyl-
4-phenyl)ethyl-2-(4-thiazolidine)carboxylic acid 5j (468 mg, 1.34
mmol) and 3-(3-pyridyl)-1-propanol (275 mg, 2.01 mmol) in the
same procedure as described in the preparation of compound 6 (409
2-Aminobenzyl (2S)-5,5-Dimethyl-1-[1,2-dioxo-2-(2,4,6-tri-
methylphenyl)]ethyl-2-(4-thiazolidine)carboxylate (44). This com-
pound was prepared from (2S)-5,5-dimethyl-1-[1,2-dioxo-2-(2,4,6-
trimethylphenyl)]ethyl-2-(4-thiazolidine)carboxylic acid 5i (449 mg,
1.34 mmol) and 2-aminobenzyl alcohol (247 mg, 2.01 mmol) in
the same procedure as described in the preparation of compound 6
1
mg, 65.2%). H NMR (600 MHz, CDCl3) δ1.41 (s, 3H), 1.44 (s,
3H), 1.71 (s, 3H), 1.88 (s, 3H), 1.96 (m, 2H), 2.67 (t, 2H, J ) 7.8
Hz), 2.74 (d, 1H, J ) 16.2 Hz), 2.97 (dd, 1H, J ) 6.0, 12.0 Hz),
3.07 (d, 1H, J ) 12.0 Hz), 3.82 (d, 1H, J ) 16.2 Hz), 4.15 (m,

4070 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14
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2H), 4.59 (d, 1H, J ) 6.0 Hz), 7.18-7.36 (m, 7H), 8.47 (m, 2H).
FAB-MS [M + H]+ )469.1 m/e. EI-HRMS: calcd for C26H33N2O4S
[M + H]+, 469.2161; found, 469.2187. Anal. (C26H32N2O4S): C,
H, N.
Chick Dorsal Root Ganglion Cultures. Dorsal root ganglia
(DRGs) were dissected from chick embryos of 8 d gestation and
inoculated in rat rail collagen-coated culture flasks. Following a 1
h of attachment at 37 °C in a humidified 5% CO2 atmosphere, the
DRGs were treated with the test compounds plus 0.15 ng/mL of
NGF in Dulbecco’s modified Eagle’s medium (DMEM). The
control groups received the same amount of NGF only. The DRGs
were further incubated in a 37 °C, 5% CO2 incubator for 48 h prior
to evaluation. The ganglia were observed under phase contrast with
an Olympus CK2 inverted microscope and were scored based on
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Acknowledgment. This work was supported by the grant
from the National “973” Project Foundation of China (No.
G1998051107) to S.L., and grants from the National Natural
Science Foundation of China (No. 30000215) and the China
Postdoctoral Science Foundation to L.Z.
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