Development of analogues of 1α,25-dihydroxyvitamin D3 with biased side-chain orientation: C20 methylated des-C,D-homo analogues

Article abstract of DOI:10.1002/ejoc.200801183

The discovery that 1α,25-dihydroxyvitamin D₃ is effective in the inhibition of cellular proliferation and in the induction of cellular differentiation has led to a search for analogues in which these activities and the classical calcemic activi

Full text of DOI:10.1002/ejoc.200801183

FULL PAPER
DOI: 10.1002/ejoc.200801183
Development of Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-
Chain Orientation: C20 Methylated Des-C,D-homo Analogues
Freek Vrielynck,[a] Dirk Van Haver,[a] Maurits Vandewalle,[a] Lieve Verlinden,[b]
Annemieke Verstuyf,[b] Roger Bouillon,[b] Gianluca Croce,[c] and Pierre De Clercq*[a]
Dedicated to Professor Alain Krief
Keywords: Vitamins / Structure–activity relationships / Conformation analysis / Calcitriol
The discovery that 1α,25-dihydroxyvitamin D3 is effective in
the inhibition of cellular proliferation and in the induction of
cellular differentiation has led to a search for analogues in
which these activities and the classical calcemic activity of
the hormone are dissociated. In this context, the synthesis
and biological evaluation are reported for six CD-ring modi-
fied structural analogues that were conceived so as to enforce
a particular orientation of the 25-hydroxylated side chain.
The analogues are characterized by the absence of the C-
ring and the presence of an unnatural six-membered D-ring.
The biased side-chain orientations are realized through the
stereocontrolled incorporation of methyl substituents at posi-
tions C13/C20 and C16/C20. Comparison of the results of the
biological evaluation and conformational analysis of the side
chain confirms the existence of a relationship between inhi-
bition of MCF-7 breast cancer cell proliferation and side
chain geometry.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Introduction
1α,25-Dihydroxyvitamin D3 (1, also known as calcitriol)
is the hormonally active form of vitamin D (Figure 1).[1]
Its potential in therapy is linked to its immunomodulatory
activity and to its ability to inhibit cellular proliferation and
to induce cellular differentiation. However, as a result of
its classical calciotropic activity, its therapeutic value in the
treatment of certain cancers is limited, as effective doses
generate calcemic side effects.[2] This has instigated an active
search for analogues of calcitriol in which the calcemic and
antiproliferative or prodifferentiating activities are sepa-
rated. In this context, various successful structural modifi-
cations have been introduced in the side chain or in the A-
ring, which are the flexible parts of the molecule.[3] As one
example, the inversion of the configuration at C20 in
calcitriol leads to derivative 2, which is several orders of
magnitude more potent than natural hormone 1 (Table 1).[4]
Figure 1. Chemical structures of calcitriol (1), 20-epi-calcitriol (2),
and a 6D analogue (3).
Our laboratory, in contrast, has focused on modifications
in the central CD-ring system.[5] Almost as a rule, these
modifications have led to a reduction in calcemic activity.[6]
As a typical example, analogue 3, a “6D analogue” in which
the C-ring has been removed (deletion of C9 and C11) and
the D-ring enlarged, possesses a similar prodifferentiating
activity as the natural hormone, but is much less calcemic
(Table 1).[7]
[a] Department of Organic Chemistry, University of Ghent,
Krijgslaan 281, 9000 Gent, Belgium.
Fax: +3292644998
E-mail: pierre.declercq@ugent.be
[b] Laboratory of Experimental Medicine and Endocrinology, K.
U. Leuven, Gasthuisberg,
Herestraat 49, 3000 Leuven, Belgium
[c] Dipartimento di Scienze e Tecnologie Avanzate, Università del
Piemonte Orientale,
via Bellini 25/G, 15100 Alessandria, Italy
1720
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Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
Table 1. Selected biological activities of 1–4.[a]
actions and in particular by the absence of syn-pentane in-
teractions.[9]
Cell differentiation and proliferation
Entry
Binding
Calcium
In this context, we have described in a previous study the
three stereoisomeric 6D analogues 4a, 4b, and 4c, featuring
the C13/C16 disubstitution pattern (Figure 3).[10] Among
the three stereoisomers, 4a with the side chain in the desired
S(g+) orientation was found to be significantly more active
than the two other stereoisomers (Table 1).
Ca serum
(mice)
VDR (pig)
HL-60
MCF-7
1
2
3
4a
4b
4c
100
88
125
20
2
100
3000
90
90
9
100
5000
300
200
30
100
800
4
4
Ͻ0.25
Ͻ0.25
2
8
70
[a] The activities are presented as relative values; the reference value
of calcitriol (1) is defined as 100%. Further details about the meth-
odology are given in the Experimental Section.
In the present work we will focus on the development of
analogues possessing side chains with biased spatial orien-
tations. Studies have shown indeed that for many analogues
there is a (qualitative) correlation between cell-differen-
tiating potency and the preferred spatial orientation of the
side chain. In particular, it was observed that the preferred
side chain orientations of many potent analogues are dis-
tributed among a restricted “active” region in space (vide
infra).[8]
In particular, we wish to describe the synthesis of 6D
analogues, which are conceived so as to favor, among three
possible side chain orientations, the one that can be associ-
ated with the active region. As shown in Figure 2, the con-
ceived 6D analogues are characterized by a cis relation be-
tween the alkyl chain at C17 and the seco-B,A-ring part of
the molecule at C14. Biased side chain orientations are in-
duced by the incorporation of two methyl groups, each one
located at a different position of the three considered posi-
tions C13, C16, and C20. Depending on the location of
the two methyl groups and the relative configuration of the
corresponding stereocenters, one of three possible orienta-
tions for the side chain will result. The side chain orienta-
tions are identified as S(g+), S(a), and S(g–) depending on
the sign and magnitude of the dihedral angle C13–C17–
C20–C22 (+60, 180, and –60°, respectively), with C22 repre-
senting the first carbon atom of what we will further con-
sider as the side chain S. The S(g+) orientation is the one
which directs the 25-hydroxy group towards the desired
active region. Among the three possible staggered confor-
mations that result from rotation at the C17–C20 bond, the
preferred one will be characterized by minimal steric inter-
Figure 3. Chemical structures of analogues 4a, 4b, and 4c with di-
hedral angle value (τ) in the preferred conformation of fragment
C13–C17–C20–C22.
Results and Discussion
In the present work we will concentrate on the methyl
disubstitution at C13/C20 and at C16/C20. In particular, we
describe herein the synthesis and biological evaluation of
analogues 5a, 5b, 6a, 6b, 7a, and 7b (Figure 4). These repre-
Figure 2. Staggered side-chain orientations in 6D analogues re-
sulting from rotation at the C17–C20 bond.
Figure 4. Chemical structures of analogues 5a, 5b, 6a, 6b, 7a, and
7b.
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P. De Clercq et al.
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sent three different pairs, each pair including the C20 epi-
mers that are identified as either the a (20R) or b (20S)
epimer. The three different series 5, 6, and 7, which are dif-
ferentiated by the location of the second methyl group and
by the configuration of the resulting stereocenters at C13
or C16, were chosen so that among the six analogues, two
of them would favor each one of the three possible orienta-
tions S(g+), S(a), or S(g–). As illustrated in Figure 5, the
desired orientation S(g+) is imposed in analogues 5a and
6b, the orientation S(a) in analogues 5b and 7a, and the
orientation S(g–) in analogues 6a and 7b. We will not con-
sider here two further analogues that would correspond to
the 13-epi-5 series featuring three vicinal substituents in the
all-cis configuration, and in which the preferred side chain
conformation would correspond to one of the undesired
orientations S(a) or S(g–).
Scheme 1. General synthetic strategy.
are observed in the two series that involve the all-equatorial
trisubstituted intermediates 12a (cf. analogues 5a,b) and
13a (cf. analogues 6a,b) and (2) the relative configurational
assignment of the stereogenic centers C14, C16, C17, and
C20 in the C16-methylated series is based on the X-ray dif-
fraction analyses of tosylate 14 (cf. analogues 6a,b) and
alcohol 15 (cf. analogues 7a,b).
The synthesis of cyclohexanone 10a (and 10b) has been
reported in detail and is summarized in Scheme 2.[12] It fea-
tures the highly enantioselective 1,4-addition of an alkenyl-
zirconocene chloride to 2-cyclohexenone by a chiral
Figure 5. Biased side-chain orientations in 5a, 5b, 6a, 6b, 7a, and
7b with the corresponding dihedral angle value (τ) in the preferred
conformation of fragment C13–C17–C20–C22 in each isomer.
Synthesis
The synthesis of analogues 5a, 5b, 6a, 6b, 7a, and 7b
starts from conjugated cyclohexenones 8 and 9. The general
strategy is depicted in Scheme 1. In the first stage, a C13 or
C16 methyl-substituted cyclohexanone (cf. 10a and 11a,b)
was obtained possessing a 1-hexenyl group with the re-
quired absolute configuration at C14. In the second stage,
a methoxycarbonylmethyl group was introduced at C17
with the required cis configuration relative to the chain at
C14 to afford key intermediates 12a, 13a, and 13b. In the
last stage, the methoxycarbonylmethyl group was used to
construct the C20 methylated analogue side chain with the
required configuration a or b at C20, and the hexenyl group
was oxidatively cleaved to generate an aldehyde function,
which enabled the well-precedented Wittig–Horner-type
coupling of the A-ring.[11]
With regard to the structural determination of the dif-
ferent stereoisomeric intermediates that will be synthesized,
it is important to note that (1) analogous stereoselectivities Scheme 2. Enantioselective synthesis of 10a.
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Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
rhodium(I) complex generated with BINAP as chiral li-
gand, a methodology which has led to the synthesis of en-
antiomerically pure 16.[13] In our case, the 1,4-addition was
performed by using (E)-1-hexenylzirconocene chloride,
prepared from 1-hexyne and Cp2Zr(H)Cl (Schwartz rea-
gent)[14] in the presence of a catalytic amount of the rhodi-
um(I) complex [Rh(cod)Cl]2 and (R)-BINAP, followed by
trapping of the O-enolate with formaldehyde.[15] This led to
a 7:3 mixture (95%) of 17a/17b with an excellent ee value
(better than 96%). After separation, aldol derivative 17a
was converted in good yield (81%) into required trans-de-
rivative 10a.
In a similar way, the asymmetric 1,4-addition with the
use of the same catalytic conditions with (R)-BINAP as chi-
ral ligand, but followed by workup with an aqueous solu-
tion of ammonium chloride, led to a 1:1 diastereomeric
mixture of 11a/11b (95% yield), which could be separated
by gradient elution chromatography (Scheme 3). Again,
both stereoisomers were obtained with an excellent ee value
(better than 96%). This result further illustrates the utility
of this methodology in obtaining absolute reagent stereo-
control.
Figure 6. Conformational behavior of 11a and 11b with relevant
1H NMR spectroscopic data: chemical shifts (δ) given in ppm.
metal reduction of the corresponding unsaturated esters
obtained by Peterson or Horner–Wadsworth–Emmons
(HWE) olefination. The choice of this methodology was
dictated by prior work in which it was observed that the
reduction of 18 (mixture of E,Z isomers) with lithium in
liquid ammonia led to saturated ester 19 in high yield with
the ethoxycarbonylmethyl side chain in the preferred equa-
torial orientation (Scheme 4).[10]
Scheme 4. Dissolving metal reduction of 18.
Whereas the Peterson olefination of cyclohexanone 10a
led to a 2:1 mixture (98% yield) of E-20/Z-20, the HWE
olefination was more stereoselective yielding the E isomer
almost exclusively (Scheme 5). Subsequent reduction of un-
saturated ester E-20 with lithium in liquid ammonia at
Scheme 3. Enantioselective synthesis of 11a and 11b.
Whereas the configurational assignment of 11a and 11b –78 °C led to saturated ester 12a with the expected trans
eventually rests on their conversion into 14 and 15 relation (80% yield). The equatorial orientation of the
(Scheme 1), respectively, the structures of which were solved methoxycarbonylmethyl group is substantiated by the large
by X-ray diffraction analysis, the difference between the sum of vicinal coupling constants of H17 (38 Hz).
trans- and cis-disubstituted cyclohexanones is also apparent
The stereochemical assignment of the E,Z isomers fol-
from NMR spectroscopic analysis (Figure 6). The assign- lows from NMR spectral analysis (Figure 7). In isomer E-
ment of the trans-relationship in 11a with diequatorial ori- 20 with the alkyl substituents in a trans-equatorial orienta-
entation of the alkyl substituents is in line with the axial tion, the equatorial H16 is strongly deshielded (δ =
orientation of H14, characterized by a large sum of vicinal 3.72 ppm); isomer Z-20 in contrast adopts the conforma-
coupling constants (37 Hz) and with the well-separated res- tion with the methyl group at C13 in the axial orientation
onances of the two protons at C13 (2.44 and 1.82 ppm for (cf. nOe between methyl and H15/H16) with a deshielding
the equatorial and axial hydrogen atoms, respectively). cis- of the equatorial H13 as a consequence (δ = 3.89 ppm).
Derivative 11b in contrast is present as an equilibrating
As shown in Scheme 6, in a similar way cyclohexanone
mixture of chair conformations, as is apparent from the 11a was subjected to the HWE conditions to afford E iso-
protons at C13, which now resonate at δ = 2.36 and mer E-21a almost exclusively (98% yield). Subsequent dis-
2.12 ppm, whereas H14 possesses a much smaller sum of solving metal reduction led, under the same conditions, to
vicinal coupling constant values (21 Hz).
the all-equatorial substituted saturated ester 13a. Again, the
Further synthesis of key intermediates 12a, 13a, and 13b Peterson olefination turned out to be much-less stereoselec-
from 10a, 11a, and 11b, respectively, proceeds by dissolving tive and afforded a 2:1 mixture of E,Z isomers. The stereo-
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P. De Clercq et al.
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chemical assignment follows from NMR spectral analysis
(Figure 7). Isomer Z-21a adopts a conformation in which
both alkyl groups are axially oriented (cf. nOe between
methyl and H13/H15), resulting in a strong deshielding of
the equatorial H16 (δ =3.95 ppm), whereas in isomer E-21a
with both alkyl substituents in a trans-diequatorial orienta-
tion the deshielded proton is the equatorial H13 (δ
=3.89 ppm).
Scheme 5. Synthesis of key intermediate 12a.
Scheme 6. Synthesis of key intermediate 13a.
In the case of epimeric cyclohexanone 11b, Peterson ole-
fination afforded a 15:85 mixture of E,Z isomers (98%
yield), which when subjected to the dissolving metal re-
duction conditions led to a 9:1 mixture of saturated esters
13b/13c (Scheme 7). As expected, Z-21b adopts a chair con-
formation with the methyl group at C16 in the axial orienta-
tion with a strong deshielding of H16 (δ =4.00 ppm) as a
consequence (Figure 7). The structural assignment of C17
epimeric esters 13b and 13c eventually rests on the obtain-
ment of alcohol 15 in a sequence starting from major ste-
reoisomer 13b (Scheme 12). As mentioned earlier, the struc-
ture of 15 has been determined unambiguously by X-ray
diffraction analysis. It is also interesting to note how the
NMR spectroscopic data of the two protons at C20 are
rather informative with respect to the configuration of satu-
rated esters 12 and 13 (Figure 8). In fact, the same pattern is
observed in all saturated esters that possess a trans relation
between the methoxycarbonylmethyl group and the vicinal
methyl substituent (i.e., 12a, 13a, and 13c).
The final stage of the synthesis of the analogues required
the construction of the calcitriol side chain with the stereo-
selective introduction of the desired C20 stereocenter that
differentiates between the a and b series of analogues.[16]
In this context, the synthesis of analogues 7a,b proceeded
through a pathway different from the one followed for the
synthesis of both 5a,b and 6a,b. Furthermore, in the case
Figure 7. Conformational behavior of E,Z-20, E,Z-21a, and Z-21b
with relevant 1H NMR spectroscopic data: chemical shifts (δ) given
in ppm.
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Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
slightly different from the one that was eventually adopted
for the effective preparation of the analogues, there should
be no relevant difference regarding the stereochemical issue.
After deprotonation of saturated ester 13a with lithium di-
isopropylamide (LDA), alkylation of the resulting enolate
anion with iodomethane led to an inseparable mixture of
stereoisomers, which was further reduced with lithium alu-
minum hydride to afford a 9:1 mixture of expected alcohols
22a/22b (Figure 9). After separation, major isomer 22a was
converted into alcohol 23a, the crystalline tosylate of which
(14) was solved by X-ray diffraction analysis (Figure 10).
Scheme 7. Synthesis of key intermediate 13b.
Scheme 8. Synthesis of tosylate 14.
Figure 8. Conformational behavior of 12a, 13a, 13b, and 13c with
Figure 9. Origin of stereoselectivity in the alkylation at C20.
1
relevant H NMR spectroscopic data: chemical shifts (δ) given in
ppm and vicinal coupling constant values are given in parentheses
(Hz).
The observed high stereoselectivity in the alkylation pro-
cess is in line with the expectation that the electrophile
would approach the enolate anion from the least-hindered
of analogues 5 and 6, a different strategy was required for si face, as illustrated in Figure 9.[17] Hence by varying the
the stereoselective synthesis of the analogues of the a series nature of the electrophile (methyl iodide or propargyl bro-
compared to the analogues of the b series. This is due to mide) as a function of the required stereochemistry at C20,
the stereoselective outcome of the alkylation of the enolate it became possible to prepare analogues 5a, 5b and ana-
anions derived from saturated esters 12a, 13a, and 13b.
logues 6a, 6b with high and predictable stereoselectivity. In
This was originally observed in an exploratory sequence the actual syntheses the hexenyl side chain is first converted
that is summarized in Scheme 8. Although this sequence is into the protected aldehyde by treatment with ozone in a
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P. De Clercq et al.
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Figure 10. ORTEP structure of 14.
solution of dichloromethane and methanol (1:1) followed
by workup with dimethyl sulfide.[18]
The synthesis of analogues 5a and 5b is further shown in
Schemes 9 and 10. Ester 12a was first converted into di-
methyl acetal 24 (70% yield). The synthesis of analogue 5a
with the natural R configuration at C20 required that the
enolate anion obtained from 24 be alkylated with the side
chain fragment and that the ester moiety be subsequently
converted into the C21 methyl group, whereas the synthesis
of analogue 5b with the S configuration at C20 required
that the C21 methyl group be introduced by alkylation and
that the ester moiety be subsequently converted into the
side chain fragment. Following this strategy, the alkylation
of the enolate anion derived from ester 24 with bromide 25a
led stereoselectively to alkyne 26 (74% yield), whereas the
analogous alkylation with iodomethane afforded ester 27
(89%).[19]
Scheme 10. Synthesis of analogues 5a and 5b via intermediates es-
ters 26 and 27.
moiety in 30, the acetal function of intermediate 31 was
hydrolyzed (triethylsilyl triflate and 2,4,6-collidine in
dichloromethane),[20] and the resulting aldehyde was imme-
diately subjected to the Wittig–Horner reaction with the
anion derived from phosphane oxide 32.[11] Desilylation fi-
nally afforded analogue 5a. Further conversion of 27 into
analogue 5b proceeded via intermediate acetal 37
(Scheme 10). After reduction of ester 27 to alcohol 33, fol-
lowed by oxidation to aldehyde 34, the latter was subjected
to a Wittig reaction involving the ylide derived from phos-
phonium bromide 35[21] to afford unsaturated side chain in
36. After hydrogenation of the alkene moiety in 36, the ace-
tal function of 37 was hydrolyzed, and the obtained alde-
hyde was immediately converted into analogue 5b in the
same way as described for the synthesis of analogue 5a.
As shown in Scheme 11 the synthesis of analogues 6a
and 6b starting from ester 13a followed the same strategy,
which implied, however, that the synthesis of the analogue
Scheme 9. Stereoselective synthesis of intermediates 26 and 27 from
ester 12a.
Further conversion of 26 into analogue 5a proceeded via in the a series (6a) would proceed via ester 39, obtained by
intermediate acetal 31 (Scheme 10). The latter was obtained alkylation of the enolate derived from 38a with iodome-
following an uneventful sequence of reactions involving the thane, whereas the synthesis of the epimeric analogue 6b
reduction of ester 26 to alcohol 28, its subsequent conver- would proceed via ester 40, obtained through similar alky-
sion into tosylate 29, followed by reduction to afford the lation but involving bromide 25b as the electrophilic reac-
C21 methyl group in 30. After hydrogenation of the alkyne tant.
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Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
Scheme 12. Synthesis of analogues 7a and 7b from ester 13b.
Scheme 11. Synthesis of analogues 6a and 6b from ester 13a.
The eventual synthesis of 6a proceeded via intermediate
42 and involved the same reaction conditions as those used
for the synthesis of 5b. The eventual synthesis of 6b pro-
ceeded via intermediate 44 and involved the same reaction
conditions as those used for the synthesis of 5a.
As shown in Scheme 12 a different strategy was adopted
for the synthesis of analogues 7a and 7b from ester 13b.
This originated from the observed lack of stereoselectivity
in the alkylation of the enolate anion derived from 38b. Pre-
sumably, the axial orientation of the methyl group at C16
is less efficient in the shielding of one side of the enolate
anion. In practice, the alkylation with iodomethane led to
a 1:1 mixture of the esters, which could not be separated at
this stage. After reduction with lithium aluminum hydride
the two obtained alcohols 46a and its C20 epimer were sep-
arated by chromatography. Fortunately, 20-epi-46a was
crystalline and its structure was unambiguously determined
as 15 by X-ray diffraction analysis (Figure 11). After a se-
quence involving oxidation of alcohol 46a to the corre-
sponding aldehyde, Wittig coupling and hydrogenation as
before, obtained acetal intermediate 47a was subjected to
the same final sequence to afford analogue 7a. In much the
same way, 7b was obtained from alcohol 15 via acetal inter-
mediate 47b.
Figure 11. ORTEP structure of 15.
plied [(i) TES triflate, 2,4,6-collidine, dichloromethane,
5 min, 0 °C; (ii) water],[20] which eventually resulted in a
more-efficient subsequent Wittig–Horner coupling process
(Scheme 13).
Scheme 13. Hydroxysilylation in the hydrolysis of dimethylacetal
45b.
Biological Evaluation
It is interesting to note that the free hydroxy group in
intermediates 47 is protected as a triethylsilyl (TES) ether
The biological evaluation of the analogues includes the
(cf. 48) when the acetal deprotection conditions were ap- determination of the binding affinity for the porcine intesti-
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nal VDR, the antiproliferative activity in vitro on breast the 3D arrangement of the ligand-binding pocket around
cancer MCF-7 cells, and the calcemic activity in vivo in calcitriol and reveals in particular that the elongated ligand
vitamin D-replete normal NMRI mice. Results are shown occupies only 56% of the accessible volume of the VDR
in Table 2.
cavity.[23] In contrast, in studies dealing with structure–
activity relationships related to the orientation of the side
chain, a few regions were identified in which the preferred
orientation of the 25-hydroxy group would correspond to
an increased cell-differentiating potency.[8] Interestingly,
these do not correspond directly with the position of the
25-hydroxy group in the VDR-calcitriol complex.
Central in this and related work is the use of conforma-
tional maps to describe the preferred geometries of the side
chain. The concept of dot maps in this area was first intro-
duced by Okamura and Midland.[24] In this approach,
force-field calculations are performed so as to generate
within a given energy window (usually 20 kJmol–1) all pos-
sible local minimum energy conformations that the side
chain may adopt. The orientation in space of each found
conformation is defined by a dot that corresponds to the
position of the 25-oxygen atom in that particular conforma-
tion. Subsequently, volume maps have been used in our
group to optimize visualization.[25] Volume maps corre-
sponding to the side-chain conformations of 5a/5b, 6a/6b,
and 7a/7b are shown in Figure 12. To a reasonable extent,
these correspond nicely with the preferred conformations
that were presented in Figure 5.
Table 2. Selected biological activities of 5–7.[a]
Entry
Binding
VDR (pig)
Cell proliferation
MCF-7
Calcium
Ca serum (mice)
1
100
35
0
0
2
0.3
0
100
90
0
0.3
90
3
100
0.5
–
–
Ͻ0.25
–
–
5a
5b
6a
6b
7a
7b
0
[a] The activities are presented as relative values; the reference value
of calcitriol (1) is defined as 100%. Further details about the meth-
odology are given in the Experimental Section.
6D-analogue 5a displays 35% of the VDR affinity com-
pared with calcitriol (100% binding). The other isomers
demonstrated only 2% (6b) or less of the affinity for the
VDR. Analogues 5a and 6b have equal potency to inhibit
the proliferation of MCF-7 cells when compared with the
activity of calcitriol, whereas the other analogues did not
show any relevant antiproliferative activity. Interestingly,
these two analogues have poor calcemic effects in vivo
(Ͻ0.25% or less compared with calcitriol).
In Figure 12 is also shown a section of a spherical region
that we have defined previously as the relative activity vol-
ume.[25] The latter is generated so that, among a pair of
epimeric analogues possessing very different activities (ide-
Conformational Analysis
Vitamin D activity is normally expressed by a genomic ally a very active and an inactive compound), a sphere is
pathway. The hormone binds with the intracellular vitamin created that contains the lowest possible mol fraction of the
D receptor (VDR) so as to regulate gene transcription and side-chain conformations of the less-active analogue, but at
synthesis of new proteins that are more directly responsible the same time contains the highest possible mol fraction of
for the biological response.[22] In view of this mechanism, the conformations of the more active of the pair. The sec-
the geometry of the VDR–calcitriol complex is crucial. This tion of this volume that is shown as a green circle in the
important information has become available through the Figure 12 was originally generated on the basis of the con-
high-resolution crystal structure of the complex that shows formational profiles of the most- and least-active stereoiso-
Figure 12. Volume maps representing the conformational behavior of the side chain of analogues 5, 6, and 7 in which the AB portion
has been deleted with inclusion of a section of the relative activity volume; front view. The position of O25 in receptor-bound conforma-
tion (black dot) is taken from ref.[23] Left: 5a (green) and 5b (pink); middle: 6a (green) and 6b (pink); right: 7a (green) and 7b (pink).
1728
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1720–1737

Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
209.5 (C=O), 133.9 (=CH), 129.3 (=CH), 48.1 (CH2), 44.4 (CH),
43.1 (CH), 34.8 (CH2), 32.5 (CH2), 32.4 (CH2), 31.9 (CH2), 22.5
(CH ), 14.8 (CH ), 14.1 (CH ) ppm. IR: ν = 2957 (s), 2928 (vs),
mers among four 22-methyl-substituted analogues de-
scribed by Yamada.[26] The occupation of this volume by
the 25-hydroxy group of the side chain was calculated to
correspond to 66, 1, 2, 67, 5, and 9% for 5a, 5b, 6a, 6b, 7a,
and 7b, respectively. As was the case for the three isomeric
6D-analogues 4a, 4b, and 4c,[10] a very nice correlation is
observed also for the 6D-analogues in the 5, 6, and 7 series
between the calculated occupancies and the biological ac-
tivity, at least with respect to the antiproliferative activity.
˜
2
3
3
2856 (s), 1714 (vs), 1457 (w), 1377 (vw), 1317 (vw), 1216 (vw), 1950
(vw), 968 (w) cm–1. MS: m/z (%) = 193 (5), 165 (5), 151 (12), 137
(26), 124 (75), 109 (48), 95 (38), 81 (73), 67 (64), 55 (53), 41 (100).
Data for 11b: Rf = 0.44 (i-octane/EtOAc, 8:2). [α]D = +20.8 (c =
1
1.0, CHCl3). H NMR (500 MHz, C6D6): δ = 5.41 (dtd, J = 15.5,
6.7, 1.4 Hz, 1 H), 5.27 (ddt, J = 15.5, 5.9, 1.3 Hz, 1 H), 2.45 (m, 1
H), 2.36 (ddd, J = 13.8, 4.9, 1.4 Hz, 1 H), 2.12 (ddd, J = 13, 5.7,
This is however not reflected when comparing the binding 1.4 Hz, 1 H), 1.97 (m, 1 H), 1.45 (m, 4 H), 1.24 (m, 4 H), 0.99 (d,
J = 6.8 Hz, 3 H), 0.84 (t, J = 6.9 Hz, 3 H) ppm. 13C NMR
affinities for the nuclear VDR, in particular when compar-
(125 MHz, C6D6): δ = 210.4 (C=O), 132.5 (=CH), 131.3 (=CH),
ing the two active compounds 5a and 6b. Presumably, the
45.2 (CH2), 44.8 (CH), 39.7 (CH), 32.7 (CH2), 31.9 (CH2), 29.7
unnatural location of the C16 methyl group is responsible
(CH ), 22.2 (CH ), 15.3 (CH ), 14.1 (CH ) ppm. IR: ν = 2958 (s),
˜
2
2
3
3
for the observed loss in affinity.
2927 (vs), 2857 (m), 1712 (vs), 1670 (vw), 1457 (m), 1376 (w), 1216
(w), 1147 (vw), 1120 (vw), 1070 (w), 981 (w) cm–1. MS: m/z (%) =
193 (7), 165 (6), 151 (16), 137 (36), 124 (97), 109 (58), 95 (45), 67
(70), 55 (59), 41 (100).
Conclusions
Representative Procedure for the Horner–Wadsworth–Emmons Ole-
fination involving Cyclohexanones 10a and 11a: To a cooled (–20 °C)
suspension of sodium hydride (4 equiv.) in tetrahydrofuran (0.7 )
was added (EtO)2P(O)CH2CO2Me (4 equiv.). After stirring for
30 min, the reaction mixture was brought to room temperature and
further stirred for 1 h. To the cooled (0 °C) mixture was added a
solution of ketone (1 equiv.) in tetrahydrofuran (0.7 ). After stir-
ring overnight at room temperature a saturated solution of sodium
hydrogen carbonate was added, and the mixture was extracted with
tert-butyl methyl ether. The combined organic phase was dried
(magnesium sulfate) and further concentrated in vacuo. The residue
was further purified by column chromatography with pentane/ethyl
acetate (98.5:1.5). From 10a (2.91 g, 15 mmol) was obtained 3.68 g
of E-20 (98%) and from 11a (3.08 g, 15.9 mmol) 3.90 g of E-21a
(98%).
Six 6D-analogues 5a, 5b, 6a, 6b, 7a, and 7b possessing
biased side-chain conformations were synthesized and their
biological activities evaluated. In this way a study is
rounded in which a series of 6D-analogues was conceived
featuring a dimethyl substitution pattern among three posi-
tions (i.e., C13, C16, and C20), the relative locations and
stereogenicities of which are determining for the orientation
of the side chain. The present study further confirms that
there exists a relationship between the preferred orientation
of the side chain and the antiproliferative activity of the
analogues that is not necessarily reflected in the measured
binding affinities for the nuclear vitamin D receptor.
Experimental Section
E-20: Rf = 0.62 (i-octane/EtOAc, 6:4). [α]D = –131.6 (c = 1.0,
CHCl3). H NMR (500 MHz, CDCl3): δ = 5.61 (s, 1 H), 5.37 (dt,
1
(2R,5R)-5-[(E)-Hex-1-enyl]-2-methylcylohexanone
(11a)
and
J = 15.1, 6.6 Hz, 1 H), 5.26 (dd, J = 15.1, 8.5 Hz, 1 H), 3.71 (m, 1
H), 3.69 (s, 3 H), 1.98 (m, 4 H), 1.87 (m, 1 H), 1.78 (m, 1 H), 1.73
(m, 1 H), 1.41 (m, 2 H), 1.31 (m, 4 H), 1.01 (d, J = 6.6 Hz, 3 H),
0.89 (t, J = 6.9 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ =
167.7 (C=O), 166.7 (=C), 134.2 (=CH), 130.7 (=CH), 110.9 (=CH),
50.8 (OCH3), 50.7 (CH), 44.3 (CH), 33.1 (CH2), 32.2 (CH2), 31.7
(CH2), 30.0 (CH2), 26.9 (CH2), 22.2 (CH2), 16.3 (CH3), 13.9 (CH3)
(2S,5R)-5-[(E)-hex-1-enyl]-2-methylcylohexanone (11b): To a solu-
tion of Cp2Zr(H)Cl (1.2 equiv.) in tetrahydrofuran (0.3 ) was
added 1-hexyne (1.2 equiv.), and the resulting mixture was stirred
at room temperature for 45 min. A solution of [Rh(cod)Cl]2 (5 mol-
%) and (R)-BINAP (6 mol-%) in tetrahydrofuran (0.05 ) in a two-
necked flask was stirred for 30 min at 20 °C. To this Rh solution
was first added 6-methyl-2-cyclohexenone (9; 2.57 g, 25 mmol,
1 equiv.), followed by the addition of the Zr solution by a double
tipped needle, and the resulting mixture was further stirred at room
temperature for 3 h. After addition of an aqueous solution of am-
monium chloride (2 ) and tert-butyl methyl ether (2 times the vol-
ume of tetrahydrofuran), the precipitate was filtered through a
short pad of Celite and silica gel. The organic phase was separated,
dried (magnesium sulfate), and concentrated in vacuo. The re-
sulting 1:1 mixture of cyclohexanones 11a and 11b (4.62 g, 95%
yield) was purified by column chromatography involving gradient
elution with pentane/ethyl acetate (from 87:13 to 75:25). The ee
(better than 96% for both derivatives) was determined by chiral
HPLC (Daicel CHIRALPAK; n-hexane/ethanol, 99:1). Data for
11a: Rf = 0.43 (i-octane/EtOAc, 8:2). [α]D = +16.0 (c = 1.1, CHCl3).
1H NMR (500 MHz, C6D6): δ = 5.24 (dtd, J = 15.3, 6.6, 0.8 Hz, 1
H), 5.17 (dd, J = 15.3, 6.4 Hz, 1 H), 2.44 (ddd, J = 13.0, 4.1, 2.2 Hz,
1 H), 2.10 (m, 1 H), 1.92 (q, J = 7.0 Hz, 2 H), 1.82 (m, 2 H), 1.60
ppm. IR: ν = 2929 (vs), 2862 (s), 1719 (vs), 1645 (s), 1442 (m), 1380
˜
(w), 1308 (w), 1164 (vs), 974 (w) cm–1. MS: m/z (%) = 250 (5) [M+],
221 (10), 219 (10), 191 (39), 179 (5), 165 (12), 152 (14), 133 (12),
121 (18), 119 (13), 105 (19), 91 (32), 81 (49), 67 (76), 55 (41), 41
(100). C16H26O2 (250.38): calcd. C 76.75, H 10.47; found C 76.12,
H 10.32.
E-21a: Rf = 0.64 (i-octane/EtOAc, 8:2). [α]D = –21.5 (c = 1.0,
1
CHCl3). H NMR (500 MHz, CDCl3): δ = 5.63 (s, 1 H), 5.49 (dt,
J = 15.5, 6.0 Hz, 1 H), 5.43 (dd, J = 15.5, 6.0 Hz, 1 H), 3.89 (ddd,
J = 12.7, 3.3, 1.8 Hz, 1 H), 3.69 (s, 3 H), 2.12 (m, 1 H), 2.07 (m, 1
H), 1.97 (m, 2 H), 1.91 (dq, J = 12.9, 3.7 Hz, 1 H), 1.78 (m, 1 H),
1.63 (t, J = 12.7 Hz, 1 H), 1.34 (qd, J = 12.9, 3.8 Hz, 1 H), 1.30
(m, 4 H), 1.15 (qd, J = 12.9, 3.8 Hz, 1 H), 1.04 (d, J = 6.5 Hz, 3
H, 3 H), 0.87 (t, J = 7.0 Hz, 3 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 167.6 (C=), 166.2 (C=O), 134.5 (=CH), 129.0 (=CH),
110.4 (=CH), 50.9 (OCH3), 42.7 (CH), 39.4 (CH), 36.6 (CH2), 36.5
(m, 1 H), 1.52 (m, 1 H), 1.26 (m, 4 H), 1.13 (qd, J = 13.2, 3.5 Hz, (CH2), 32.9 (CH2), 32.3 (CH2), 31.7 (CH2), 22.2 (CH2), 18.0 (CH3),
1 H), 1.04 (d, J = 6.5 Hz, 3 H), 1.02 (qd, J = 13.1, 3.3 Hz, 1 H), 14.0 (CH ) ppm. IR: ν = 2957 (s), 2926 (vs), 2854 (s), 1721 (vs),
0.89 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (125 MHz, C6D6): δ = 1647 (m), 1458 (m), 1434 (m), 1387 (w), 1336 (w), 1234 (m), 1191
˜
3
Eur. J. Org. Chem. 2009, 1720–1737
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1729

P. De Clercq et al.
(m), 1161 (m), 1013 (w) cm–1. MS: m/z (%) = 250 (28), 219 (13), 235 (3), 219 (12), 207 (5), 191 (35), 179 (12), 165 (30), 161 (15), 147
FULL PAPER
191 (17), 161 (18), 147 (11), 133 (14), 119 (17), 107 (22), 105 (23),
91 (34), 81 (35), 67 (56), 55 (44), 41 (100).
(17), 133 (28), 119 (32), 107 (32), 105 (36), 93 (41), 79 (46), 67 (63),
55 (39), 41 (100).
Representative Procedure for the Peterson Olefination involving Cy-
clohexanones 10a, 11a, and 11b: To a cooled solution of lithium
diisopropylamide (1.2 equiv.) in tetrahydrofuran obtained by ad-
dition of n-butyllithium (2.5  in n-hexane, 1.2 equiv.) to a solution
of diisopropylamine (1.2 equiv.) in tetrahydrofuran (0.5) was added
Representative Procedure for the Dissolving Metal Reduction with
Lithium in Liquid Ammonia involving Unsaturated Esters E-20 and
E-21a and the Mixture E,Z-21b: To
a solution of lithium
(2.5 equiv.) in liquid ammonia was added at –75 °C a solution of
the unsaturated ester (1 equiv.) in diethyl ether (0.2 ). After stir-
TMSCH2COOMe (1.2 equiv.) dropwise at –78 °C. After stirring at ring for 45 min at –60 °C 2-bromo-2-methylpropane was added un-
–78 °C for 30 min, the ketone (1.2 equiv.) was added. The resulting
mixture was stirred for 1 h at –78 °C, and subsequently for another
1 h at 20 °C. After addition of a saturated solution of ammonium
chloride and extraction with tert-butyl methyl ether, the organic
phase was dried (magnesium sulfate) and concentrated in vacuo.
The mixture of esters was further separated by column chromatog-
raphy with pentane/ethyl acetate (98:2). In the case of 10a (1.75 g,
9 mmol) a 2:1 mixture of E,Z-20 was obtained (2.21 g, 98% yield);
til appearance of the red color of triphenyllithium. After addition
of ammonium chloride, tert-butyl methyl ether was added to the
white suspension and the ammonia gas was allowed to evaporate.
The resulting suspension was filtered through a short pad of silica
gel. After concentration of the filtrate in vacuo, the residue was
purified by column chromatography with pentane/ethyl acetate
(99:1) followed by HPLC with cyclohexane/tert-butyl methyl ether
(99.5:0.5) to yield the saturated ester as an oil. The reduction of E-
in the case of 11a (0.972 g, 5 mmol) a 2:1 mixture of E,Z-21a 20 (3.08 g, 12.3 mmol) and E-21a (2.0 g, 7.99 mmol) gave 12a
(1.23 g, 98% yield). In the case of 11b (3.87 g, 20 mmol) a 15:85
mixture of E-21b and Z-21b (4.91 g, 98% yield) was obtained,
which was not separated by chromatography but directly subjected
to dissolving metal reduction.
(2.48 g, 80% yield) and 13a (1.86 g, 92% yield), respectively. In
the case of E,Z-21b (1.95 g, 7.8 mmol) purification of the reaction
mixture led to a 9:1 mixture (1.50 g, 76% yield) of 13b and 13c.
12a: Rf = 0.60 (i-octane/EtOAc, 6:4). [α]D = –14.0 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 5.35 (dt, J = 15.1, 6.6 Hz, 1 H),
5.14 (dd, J = 15.1, 8.5 Hz, 1 H), 3.66 (s, 3 H), 2.57 (dd, J = 14.8,
Z-20: Rf = 0.50 (i-octane/EtOAc, 8:2). 1H NMR (500 MHz,
CDCl3): δ = 5.64 (d, J = 1.7 Hz, 1 H), 5.40 (m, 2 H), 3.89 (td, J =
7.2, 2.4 Hz, 1 H), 3.68 (s, 3 H), 2.39 (m, 1 H), 2.27 (m, 1 H), 2.04 4.1 Hz, 1 H), 2.03 (dd, J = 14.8, 8.8 Hz, 1 H), 1.97 (m, 2 H), 1.69
(m, 1 H), 1.96 (m, 2 H), 1.86 (m, 1 H), 1.64 (m, 2 H), 1.43 (m, 1
(m, 2 H), 1.60 (m, 2 H), 1.48 (m, 1 H), 1.31 (m, 5 H), 1.11 (qd, J
H), 1.29 (m, 4 H), 1.19 (d, J = 7.2 Hz, 3 H), 0.88 (t, J = 7.0 Hz, 3 = 12.9, 2.8 Hz, 1 H), 1.03 (m, 1 H), 0.88 (m, 7 H) ppm. 13C NMR
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 166.7 (C=O), 166.5 (125 MHz, CDCl3): δ = 174.1 (C=O), 135.3 (=CH), 130.1 (=CH),
(=C), 133.2 (=CH), 130.7 (=CH), 114.2 (=CH), 50.9 (OCH3), 44.3
(CH), 36.1 (CH), 33.2 (CH2), 32.7 (CH2), 26.0 (CH2), 22.6 (CH2), (CH2), 32.7 (CH2), 32.2 (CH2), 31.8 (CH2), 25.6 (CH2), 22.2 (CH2),
22.1 (CH ), 19.1 (CH ), 16.8 (CH ) ppm. IR: ν = 2932 (vs), 2871 17.4 (CH ), 13.9 (CH ) ppm. IR: ν = 2957 (s), 2924 (vs), 2854 (s),
51.4 (OCH3), 48.6 (CH), 41.2 (CH), 41.0 (CH), 39.6 (CH2), 34.1
˜
˜
2
3
3
3
3
(s), 1718 (vs), 1642 (s), 1458 (m), 1435 (s), 1385 (m), 1220 (s), 1162 1741 (vs), 1458 (m), 1438 (m), 1338 (w), 1247 (w), 1194 (m), 1169
(vs), 1122 (w), 1024 (m), 968 (m), 915 (m) cm–1. MS: m/z (%) = (m), 1131 (m), 969 (m) cm–1. MS: m/z (%) = 252 (12) [M+], 221
250 (36) [M+], 221 (24), 191 (95), 179 (14), 165 (26), 152 (20), 139
(8), 192 (8), 178 (51), 167 (19), 149 (12), 136 (21), 121 (25), 108
(39), 133 (35), 121 (44), 105 (50), 91 (62), 79 (76), 67 (100), 55 (58). (80), 95 (43), 81 (41), 79 (40), 67 (51), 55 (56), 41 (100). C16H28O2
(252.38): calcd. C 76.14, H 11.18; found C 74.67, H 10.94.
Z-21a: Rf = 0.64 (i-octane/EtOAc, 8:2). 1H NMR (500 MHz,
CDCl3): δ = 5.55 (d, J = 1.8 Hz, 1 H), 5.41 (m, 2 H), 3.95 (m, 1 13a: Rf = 0.49 (i-octane/EtOAc, 8:2). [α]D = +1.5 (c = 1.0, CHCl3).
H), 3.67 (s, 3 H), 3.65 (ddd, J = 13.8, 5.7, 1.8 Hz, 1 H), 2.58 (m, 1
H), 2.00 (m, 1 H), 1.96 (m, 2 H), 1.92 (m, 1 H), 1.78 (m, 1 H), 1.40
1H NMR (500 MHz, CDCl3): δ = 5.46 (dd, J = 15.6, 5.7 Hz, 1 H),
5.40 (dt, J = 15.6, 5.8 Hz, 1 H), 3.66 (s, 3 H), 2.51 (dd, J = 14.8,
(m, 1 H), 1.37 (m, 1 H), 1.28 (m, 4 H), 1.15 (d, J = 7.1 Hz, 3 H), 5.4 Hz, 1 H), 2.34 (m, 1 H), 2.11 (dd, J = 14.8, 8.6 Hz, 1 H), 2.0
0.87 (t, J = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ =
166.5 (C=), 165.8 (C=O), 132.0 (=CH), 130.4 (=CH), 114.1 (=CH),
50.6 (OCH3), 38.1 (CH), 37.6 (CH), 32.1 (CH2), 31.6 (CH2), 30.8
(m, 2 H), 1.79 (m, 1 H), 1.64 (dt, J = 13.4, 4.7 Hz, 1 H), 1.45–1.57
(m, 3 H), 1.24–1.36 (m, 7 H), 0.93 (d, J = 6.2 Hz, 3 H), 0.89 (t, J
= 7.0 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 174.0
(CH2), 27.5 (CH2), 25.7 (CH2), 22.0 (CH2), 18.5 (CH3), 13.8 (CH3) (C=O), 133.9 (=CH), 129.5 (=CH), 51.4 (OCH3), 39.2 (CH2), 36.2
ppm. IR: ν = 2956 (s), 2928 (vs), 2857 (m), 1720 (vs), 1646 (m), (CH), 35.7 (CH), 35.5 (CH2), 35.5 (CH), 32.7 (CH2), 32.3 (CH2),
˜
1459 (m), 1434 (m), 1386 (w), 1368 (w), 1233 (s), 1191 (m), 1160
(vs), 1144 (m) cm–1. MS: m/z (%) = 250 (27), 219 (10), 191 (19),
165 (21), 147 (11), 133 (17), 119 (17), 107 (23), 105 (23), 91 (31),
81 (38), 67 (55), 55 (44), 41 (100).
29.9 (CH2), 29.4 (CH2), 22.2 (CH2), 19.8 (CH3), 14.0 (CH3) ppm.
IR: ν = 2955 (s), 2923 (vs), 2855 (s), 1741 (vs), 1458 (m), 1436 (m),
˜
1377 (w), 1343 (w), 1283 (w), 1160 (m), 968 (m) cm–1. MS: m/z (%)
= 252 (42) [M+], 220 (19), 203 (7), 192 (33), 178 (99), 163 (12), 149
(39), 135 (21), 121 (39), 108 (43), 93 (61), 79 (44), 67 (43), 55 (49),
41 (100).
Z-21b: Rf = 0.50 (i-octane/EtOAc, 8:2). [α]D = –4.6 (c = 1.0,
1
CHCl3). H NMR (500 MHz, CDCl3): δ = 5.56 (d, J = 1.5 Hz, 1
H), 5.40 (dt, J = 15.4, 5.7 Hz, 1 H), 5.34 (dd, J = 15.4, 5.4 Hz, 1 13b: Rf = 0.46 (i-octane/EtOAc, 8:2). [α]D = –3.5 (c = 1.0, CHCl3).
H), 4.00 (m, 1 H), 3.66 (s, 3 H), 2.20 (td, J = 13.4, 1.5 Hz, 1 H),
1H NMR (500 MHz, CDCl3): δ = 5.36 (dt, J = 15.5, 6.1 Hz, 1 H),
2.05 (m, 1 H), 2.02 (m, 1 H), 1.96 (m, 2 H), 1.55 (m, 2 H), 1.50 5.31 (dd, J = 15.5, 5.7 Hz, 1 H), 3.67 (s, 3 H), 2.25 (dd, J = 14.6,
(m, 2 H), 1.30 (m, 4 H), 1.11 (d, J = 7.2 Hz, 3 H), 0.87 (t, J = 6.9 Hz, 1 H), 2.15 (dd, J = 14.6, 7.9 Hz, 1 H), 2.05 (m, 1 H), 1.96
7.0 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 166.96 (C=), (m, 2 H), 1.92 (m, 1 H), 1.84 (m, 1 H), 1.57 (m, 2 H), 1.44 (m, 2
166.89 (C=O), 134.05 (=CH), 129.03 (=CH), 112.97 (=CH), 50.80
H), 1.30 (m, 4 H), 1.20 (m, 1 H), 1.03 (m, 1 H), 0.88 (t, J = 7.1 Hz,
(CH3), 43.80 (CH), 39.50 (CH), 32.25 (CH2), 32.18 (CH2), 32.72 3 H), 0.89 (d, J = 7.2 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3):
(CH2), 30.07 (CH2), 27.16 (CH2), 22.19 (CH2), 18.29 (CH3), 13.97 δ = 173.78 (C=O), 135.65 (=CH), 128.13 (=CH), 51.43 (OCH3),
(CH ) ppm. IR: ν = 2954 (m), 2926 (s), 2855 (m), 1720 (vs), 1644 40.92 (CH), 39.47 (CH2), 37.28 (CH), 33.12 (CH2), 32.94 (CH2),
˜
3
(m), 1463 (w), 1433 (m), 1385 (w), 1367 (vw), 1242 (m), 1191 (m), 32.31 (CH2), 31.83 (CH2), 30.60 (CH), 26.58 (CH2), 22.20 (CH2),
1153 (vs), 1023 (w), 854 (vw) cm–1. MS: m/z (%) = 250 (59) [M+], 13.98 (CH ), 11.90 (CH ) ppm. IR: ν = 2957 (s), 2922 (vs), 2854
˜
3
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1730
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1720–1737

Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
(s), 1741 (vs), 1465 (w), 1436 (m), 1381 (w), 1253 (w), 1193 (m), (w), 704 (vw) cm–1. MS: m/z (%) = 209 (1), 181 (1), 169 (3), 149
1174 (m), 1124 (w), 997 (vw), 968 (m) cm–1. MS: m/z (%) = 252
(43) [M+], 221 (26), 193 (51), 178 (69), 149 (39), 135 (28), 121 (42),
108 (79), 93 (63), 79 (50), 67 (46), 55 (46), 41 (100).
(3), 124 (2), 107 (6), 95 (5), 75 (100), 67 (12), 51 (10).
38b: Rf = 0.55 (i-octane/EtOAc, 1:1). [α]D = +8.0 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.99 (d, J = 6.8 Hz, 1 H), 3.66
(s, 3 H), 3.32 (s, 6 H), 2.23 (dd, J = 14.8, 7.7 Hz, 1 H), 2.15 (dd, J
= 14.8, 7.3 Hz, 1 H), 2.01 (m, 1 H), 1.84 (m, 1 H), 1.67 (m, 1 H),
1.56 (m, 2 H), 1.49 (m, 2 H), 1.16 (m, 1 H), 0.97 (q, J = 12.6 Hz,
1 H), 0.81 (d, J = 7.0 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3):
δ = 173.6 (C=O), 108.4 (CH), 53.7 (OCH3), 51.5 (2ϫOCH3), 40.4
(CH), 39.4 (CH2), 36.9 (CH), 32.5 (CH2), 30.6 (CH), 27.7 (CH2),
13c: Rf = 0.49 (i-octane/EtOAc, 8:2). [α]D = +1.5 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 5.46 (dd, J = 15.6, 5.7 Hz, 1 H),
5.40 (dt, J = 15.6, 5.8 Hz, 1 H), 3.66 (s, 3 H), 2.51 (dd, J = 14.8,
5.4 Hz, 1 H), 2.34 (m, 1 H), 2.11 (dd, J = 14.8, 8.6 Hz, 1 H), 2.00
(m, 2 H), 1.79 (m, 1 H), 1.64 (dt, J = 13.4, 4.7 Hz, 1 H), 1.45–1.57
(m, 3 H), 1.47 (m, 3 H), 1.24–1.36 (m, 7 H), 0.93 (d, J = 6.2 Hz, 3
H), 0.89 (t, J = 7.0 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3):
δ = 174.0 (C=O), 133.9 (=CH), 129.5 (=CH), 51.4 (OCH3), 39.2
(CH2), 36.2 (CH), 35.7 (CH), 35.5 (CH2), 35.5 (CH), 32.7 (CH2),
32.3 (CH2), 29.9 (CH2), 29.4 (CH2), 22.2 (CH2), 19.8 (CH3), 14.00
21.2 (CH ), 11.8 (CH ) ppm. IR: ν = 2948 (s), 2830 (w), 1738 (vs),
˜
2
3
1456 (w), 1440 (m), 1382 (w), 1256 (m), 1193 (s), 1158 (s), 1134 (s),
1055 (s), 966 (w) cm–1. MS: m/z (%) = 212 (25), 181 (8), 138 (100),
123 (44), 106 (45), 91 (28), 74 (22), 67 (14), 55 (25), 41 (42).
(CH ) ppm. IR: ν = 2955 (s), 2923 (s), 2855 (s), 1741 (vs), 1458
˜
3
Representative Procedure for the Alkylation of Esters 24 and 38a
involving Propargyl Bromides 25a and 25b: To a solution of lithium
diisopropylamide [obtained from diisopropylamine (1.5 equiv.) and
n-butyllithium (2.5  in n-hexane, 1.5 equiv.)] in tetrahydrofuran
(0.5 ) was added dropwise at –40 °C a solution of the ester
(1.0 equiv.) in tetrahydrofuran (0.3 ). After stirring for 1 h at
–40 °C, propargylic bromide 25a or 25b (3 equiv.) was added drop-
wise. After 30 min the reaction mixture was warmed to 20 °C and
further stirred overnight. After addition of a saturated solution of
ammonium chloride the aqueous phase was extracted with tert-
butyl methyl ether and the organic phase dried (magnesium sul-
fate). After concentration in vacuo the residue was purified by col-
umn chromatography with pentane/ethyl acetate (98:2) to afford
the alkylated esters. From 24 (0.14 g, 0.57 mmol) was obtained
0.19 g of 26 (74% yield) and from 38a (0.29 g, 1.2 mmol) 0.37 g of
40 (68% yield).
(m), 1436 (m), 1377 (w), 1343 (w), 1256 (m), 1193 (s), 1158 (s),
1134 (s), 1055 (s), 966 (w) cm–1. MS: m/z (%) = 212 (25), 181 (8),
138 (100), 123 (44), 106 (45), 91 (28), 74 (22), 67 (14), 55 (25), 41
(42).
Representative Procedure for the Oxidative Cleavage of the Hexenyl
Side Chain in Esters 12a, 13a and 13b: To a cooled (–40 °C) solution
of the alkene (1 equiv.) in dichloromethane/methanol (1:1, 0.1 )
was passed a stream of ozone until appearance of a light-blue color.
A stream of nitrogen was subsequently led through the solution
until disappearance of the blue color, and the temperature was
raised to –20 °C. After addition of dimethyl sulfide (5 equiv.) and
overnight stirring at room temperature, a saturated solution of so-
dium hydrogen carbonate was added, and the resulting mixture was
partly concentrated in vacuo. The aqueous phase was further ex-
tracted with tert-butyl methyl ether, and the resulting organic phase
was dried (magnesium sulfate). After concentration in vacuo, the
residue was purified by column chromatography with pentane/ethyl
acetate (9:1) to afford the pure acetals. From 12a (0.61 g, 2.4 mmol)
was obtained 0.41 g of 24 (70% yield), from 13a (1.15 g, 4.6 mmol)
0.87 g of 38a (79% yield), and from 13b (1.34 g, 5.29 mmol) 1.06 g
of 38b (82% yield).
26: Rf = 0.55 (i-octane/EtOAc, 7:3). [α]D = –15.1 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.32 (d, J = 2.8 Hz, 1 H), 3.70
(s, 3 H), 3.43 (s, 3 H), 3.39 (s, 3 H), 2.97 (ddd, J = 9.5, 4.4, 3.5 Hz,
1 H), 2.51 (dd, J = 16.7, 9.8 Hz, 1 H), 2.22 (dd, J = 16.7, 4.4 Hz,
1 H), 1.79 (m, 2 H), 1.56 (m, 1 H), 1.47 (m, 1 H), 1.43 (m, 1 H),
1.41 (s, 6 H), 1.33 (m, 1 H), 1.15 (m, 2 H), 1.08 (qd, J = 12.3,
3.5 Hz, 1 H), 1.01 (d, J = 6.3 Hz, 3 H), 0.95 (t, J = 7.9 Hz, 9 H),
0.64 (d, J = 7.9 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ =
174.9 (C=O), 107.8 (CH), 85.9 (C), 81.2 (C), 66.2 (C), 56.7 (OCH3),
56.2 (OCH3), 51.7 (OCH3), 47.3 (CH), 46.0 (CH), 45.8 (CH), 34.9
(CH), 33.2 (2ϫCH3), 27.0 (CH2), 25.5 (CH2), 24.4 (CH2), 15.9
24: Rf = 0.44 (i-octane/EtOAc, 7:3). [α]D = –4.6 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.32 (d, J = 2.5 Hz, 1 H), 3.66
(s, 3 H), 3.43 (s, 3 H), 3.39 (s, 3 H), 2.58 (dd, J = 14.8, 4.1 Hz, 1
H), 2.02 (dd, J = 14.8, 8.8 Hz, 1 H), 1.80 (m, 1 H), 1.75 (m, 1 H),
1.69 (m, 1 H), 1.60 (m, 1 H), 1.33 (m, 1 H), 1.19 (m, 3 H), 1.02
(qd, J = 12.4, 3.5 Hz, 1 H), 0.96 (d, J = 6.3 Hz, 3 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 174.2 (C=O), 107.8 (CH), 56.8
(OCH3), 56.0 (OCH3), 51.4 (OCH3), 47.0 (CH), 41.0 (CH), 39.5
(CH2), 37.6 (CH), 32.8 (CH2), 25.4 (CH2), 24.3 (CH2), 16.2 (CH3)
(CH ), 14.9 (CH ), 7.0 (CH ), 6.2 (CH ) ppm. IR: ν = 2952 (vs),
˜
3
3
3
2
2876 (s), 2831 (m), 2240 (vw), 1739 (vs), 1542 (vw), 1451 (m), 1375
(m), 1313 (m), 1244 (s), 1165 (vs), 1078 (s), 1037 (vs), 954 (m), 926
(m), 740 (s) cm–1. MS: m/z (%) = 425 (14), 335 (5), 219 (4), 191 (8),
159 (17), 143 (6), 117 (17), 87 (10), 75 (100), 47 (19). C25H46O5Si
(454.72): calcd. C 66.03, H 10.20; found C 65.38, H 10.11.
ppm. IR: ν = 2931 (s), 2858 (m), 1737 (vs), 1440 (m), 1372 (m),
˜
1293 (w), 1252 (m), 1198 (m), 1168 (m), 1121 (s), 1075 (s), 1019
(w), 961 (w) cm–1. MS: m/z (%) = 243 [M+], 118 (4), 149 (3), 138
(5), 121 (4), 107 (9), 95 (8), 79 (8), 75 (100), 59 (11), 47 (17), 41
(15). C13H24O4 (244.32): calcd. C 63.91, H 9.90; found C 63.38, H
9.76.
40: Rf = 0.42 (i-octane/EtOAc, 7:3). [α]D = –11.5 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.84 (d, J = 6.6 Hz, 1 H), 3.57
(s, 3 H), 3.19 (s, 3 H), 3.18 (s, 3 H), 2.78 (dt, J = 9.1, 3.8 Hz, 1 H),
38a: Rf = 0.53 (i-octane/EtOAc, 1:1). [α]D = –28.5 (c = 1.0, CHCl3). 2.40 (dd, J = 16.7, 10.1 Hz, 1 H), 2.10 (dd, J = 16.7, 4.7 Hz, 1 H),
1H NMR (500 MHz, CDCl3): δ = 3.96 (d, J = 7.0 Hz, 1 H), 3.65
(s, 3 H), 3.31 (s, 6 H), 2.53 (dd, J = 15.1, 4.4 Hz, 1 H), 2.05 (dd, J
= 15.1, 8.8 Hz, 1 H), 1.77 (m, 1 H), 1.73 (m, 2 H), 1.65 (m, 1 H),
1.45 (m, 1 H), 1.07 (m, 1 H), 1.02 (m, 2 H), 0.89 (d, J = 6.3 Hz, 3
1.63 (m, 2 H), 1.45 (m, 2 H), 1.37 (m, 1 H), 1.26 (s, 6 H), 1.19 (m,
1 H), 0.90 (m, 2 H), 0.83 (d, J = 6.6 Hz, 3 H), 0.74 (q, J = 12.0 Hz,
1 H), 0.72 (s, 9 H), 0.00 (s, 6 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 174.7 (C=O), 108.4 (CH), 86.1 (C), 81.2 (C), 66.3 (C-
H), 0.82 (q, J = 12.6 Hz, 1 H) ppm. 13C NMR (125 MHz, CDCl3): O), 54.1 (OCH3), 53.7 (OCH3), 51.7 (OCH3), 46.4 (CH), 45.4 (CH),
δ = 173.9 (C=O), 108.4 (CH), 53.7 (2ϫOCH3), 51.4 (OCH3), 40.6 40.4 (CH), 35.2 (CH2), 34.3 (CH), 33.1 (2ϫCH3), 28.9 (CH2), 27.5
(CH), 40.1 (CH), 39.3 (CH2), 37.0 (CH), 34.9 (CH2), 34.0 (CH2), (CH2), 25.7 (3ϫCH3), 19.8 (CH3), 17.9 (SiC), 15.3 (CH2), –3.1
27.6 (CH ), 19.8 (CH ) ppm. IR: ν = 2949 (m), 2917 (m), 2849 (m),
(2ϫSiCH ) ppm. IR: ν = 2981 (m), 2952 (vs), 2929 (vs), 2856 (s),
˜
˜
2
3
3
1735 (vs), 1437 (m), 1369 (w), 1347 (w), 1273 (w), 1222 (m), 1195
(m), 1162 (s), 1132 (vs), 1092 (s), 1076 (s), 1054 (vs), 957 (m), 903
1740 (vs), 1462 (m), 1436 (m), 1376 (m), 1360 (m), 1248 (s), 1161
(vs), 1135 (m), 1038 (vs), 960 (w), 906 (w), 837 (s), 777 (s) cm–1.
Eur. J. Org. Chem. 2009, 1720–1737
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1731

P. De Clercq et al.
MS: m/z (%) = 398 (9), 365 (5), 307 (5), 199 (6), 159 (13), 131 (4), (m, 1 H), 2.00 (dd, J = 16.5, 9.8 Hz, 1 H), 1.80 (m, 2 H), 1.68 (dd,
FULL PAPER
107 (9), 89 (15), 75 (100), 47 (14).
J = 6.6, 4.4 Hz, 1 H), 1.53 (m, 1 H), 1.44 (s, 6 H), 1.42 (m, 1 H),
1.32 (m, 1 H), 1.29 (m, 1 H), 1.15 (m, 2 H), 0.99 (m, 1 H), 0.96
(m, 12 H), 0.65 (d, J = 7.9 Hz, 3 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 107.9 (CH), 86.9 (C), 81.8 (C), 66.3 (C), 66.0
(CH2OH), 56.8 (OCH3), 56.1 (OCH3), 47.4 (CH), 44.4 (CH), 40.2
(CH), 34.7 (CH), 33.2 (2ϫCH3), 25.8 (CH2), 25.6 (CH2), 24.4
Representative Procedure for the Methylation of Esters 24, 38a, and
38b: To a solution of lithium diisopropylamide [obtained from di-
isopropylamine (2.0 equiv.) and n-butyllithium (2.5  in n-hexane,
2.0 equiv.)] in tetrahydrofuran (1.5 ) was added dropwise at
–78 °C a solution of the ester (1.0 equiv.) in tetrahydrofuran (0.3 ).
After stirring for 1 h at –78 °C, iodomethane (5 equiv.) was added
dropwise. After stirring for 2 h water was added to the reaction
mixture. After extraction with tert-butyl methyl ether, the organic
phase was dried (magnesium sulfate) and concentrated in vacuo.
The residue was purified by column chromatography with pentane/
ethyl acetate (93:7) to afford the methylated ester(s) as an oil. Fur-
ther purification was performed by HPLC with cyclohexane/tert-
butyl methyl ether (9:1). From ester 24 (0.5 g, 2.0 mmol) was ob-
tained ester 27 (ratio 92:8; 0.47 g, 89% yield); from ester 38a
(0.32 g, 1.3 mmol) ester 39 (ratio 94:6; 0.29 g, 87% yield); in the
case of 38b (0.75 g, 3.1 mmol) a 1:1 mixture of epimeric esters 45
(0.8 g) was obtained, which was not separated but directly reduced
with lithium aluminum hydride.
(CH ), 15.9 (CH ), 15.7 (CH ), 7.0 (CH ), 6.1 (CH ) ppm. IR: ν =
˜
2
3
3
3
2
3432 (m), 2931 (m), 2874 (m), 1458 (m), 1375 (m), 1244 (m), 1157
(s), 1120 (m), 1070 (s), 1032 (vs), 961 (m), 767 (m), 741 (vs), 725
(vs) cm–1. MS: m/z (%) = 379 (1), 365 (8), 333 (4), 305 (1), 263 (1),
243 (10), 213 (8), 173 (9), 145 (8), 117 (11), 103 (12), 75 (100), 47
(14).
43: Rf = 0.24 (i-octane/EtOAc, 7:3). [α]D = –18.1 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.96 (d, J = 6.6 Hz, 1 H), 3.83
(dd, J = 10.8, 6.6 Hz, 1 H), 3.57 (dd, J = 10.8, 6.6 Hz, 1 H), 3.32
(s, 3 H), 3.31 (s, 3 H), 2.23 (dd, J = 16.4, 4.4 Hz, 1 H), 2.11 (m, 1
H), 2.01 (dd, J = 16.4, 9.5 Hz, 1 H), 1.74 (m, 2 H), 1.59 (m, 3 H),
1.41 (s, 6 H), 1.29 (m, 1 H), 1.24 (m, 1 H), 1.02 (m, 2 H), 0.90 (d,
J = 6.0 Hz, 3 H), 0.84 (s, 9 H), 0.78 (q, J = 12.3 Hz, 1 H), 0.13 (s,
6 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 108.6 (CH), 87.0 (C),
81.9 (C), 66.4 (CO), 65.6 (CH2OH), 54.1 (OCH3), 53.5 (OCH3),
44.0 (CH), 40.5 (CH), 40.4 (CH), 35.4 (CH2), 33.9 (CH), 33.1
(2ϫCH3), 27.8 (CH2), 27.2 (CH2), 25.7 (3ϫCH3), 19.8 (CH3), 17.9
27: Rf = 0.44 (i-octane/EtOAc, 7:3). [α]D = –44.3 (c = 1.86, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.32 (d, J = 1.9 Hz, 1 H), 3.66
(s, 3 H), 3.44 (s, 3 H), 3.40 (s, 3 H), 2.83 (dq, J = 7.3, 3.8 Hz, 1 H),
1.78 (m, 2 H), 1.61 (m, 1 H), 1.35 (m, 2 H), 1.29 (m, 1 H), 1.19
(m, 1 H), 1.14 (m, 2 H), 0.99 (d, J = 7.3 Hz, 3 H), 0.94 (d, J =
5.7 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 177.1 (C=O),
107.9 (CH), 56.8 (OCH3), 56.1 (OCH3), 51.6 (OCH3), 47.2 (CH),
45.5 (CH), 40.0 (CH), 34.6 (CH), 26.6 (CH2), 25.6 (CH2), 24.5
(SiC), 15.9 (CH ), –2.9 (2ϫSiCH ) ppm. IR: ν = 3430 (br. s, m),
˜
2
3
2952 (vs), 2929 (vs), 2856 (s), 2235 (vw), 1472 (m), 1462 (m), 1377
(m), 1360 (m), 1248 (s), 1160 (vs), 1040 (vs), 957 (w), 905 (w), 837
(s), 776 (s), 681 (w) cm–1. MS: m/z (%) = 337 (3), 305 (4), 279 (1),
231 (1), 213 (3), 203 (2), 171 (4), 145 (5), 133 (5), 107 (7), 91 (8),
75 (100), 47 (15), 41 (13).
(CH ), 15.0 (CH ), 9.0 (CH ) ppm. IR: ν = 2972 (m), 2929 (s),
˜
2
3
3
2831 (m), 1736 (vs), 1449 (m), 1372 (m), 1305 (m), 1199 (s), 1140
(s), 1072 (s), 1047 (m), 962 (m), 852 (w), 768 (vw) cm–1. MS: m/z
(%) = 227 [M+], 195 (2), 138 (3), 123 (1), 107 (7), 95 (3), 88 (3), 75
(100), 59 (7), 55 (7), 47 (9).
The Three-Step Sequence to Intermediates 31 and 44
Step 1: To a solution of alcohol 28 (1.0 equiv., 0.14 g, 0.32 mmol) in
dichloromethane (0.1 ) was added triethylamine (4 equiv.), tosyl
chloride (3.0 equiv.), and a catalytic amount of 4-dimethylami-
nopyridine at 0 °C. After stirring for 4 h at room temperature water
was added to the reaction mixture. After extraction with dichloro-
methane, the organic phase was dried (magnesium sulfate) and con-
centrated in vacuo. The residue was purified by column chromatog-
raphy with pentane/ethyl acetate (92:8), yielding 0.31 g (90% yield)
39: Rf = 0.41 (i-octane/EtOAc, 4:6). [α]D = –5.2 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.95 (d, J = 6.9 Hz, 1 H), 3.66
(s, 3 H), 3.31 (s, 3 H), 3.29 (s, 3 H), 2.77 (qd, J = 7.1, 3.6 Hz, 1 H),
1.74 (m, 2 H), 1.63 (m, 1 H), 1.55 (tt, J = 11.5, 3.6 Hz, 1 H), 1.42
(m, 1 H), 1.20 (m, 1 H), 1.04 (m, 2 H), 0.99 (d, J = 7.3 Hz, 3 H),
0.89 (q, J = 12.5 Hz, 1 H), 0.88 (d, J = 6.3 Hz, 3 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 176.9 (C=O), 108.5 (CH), 53.8
(OCH3), 53.7 (OCH3), 51.6 (OCH3), 45.1 (CH), 40.3 (CH), 40.1
(CH), 35.1 (CH2), 33.9 (CH), 28.3 (CH2), 27.6 (CH2), 19.5 (CH3),
of tosylate 29 as an oil. Rf = 0.48 (i-octane/EtOAc, 7:3). [α]D
=
+13.3 (c = 1.0, CHCl3). 1H NMR (500 MHz, CDCl3): δ = 7.80 (d,
J = 8.2 Hz, 2 H), 7.34 (d, J = 8.2 Hz, 2 H), 4.30 (d, J = 2.5 Hz, 1
H), 4.16 (dd, J = 9.5, 5.2 Hz, 1 H), 3.93 (t, J = 9.5 Hz, 1 H), 3.42
(s, 3 H), 3.39 (s, 3 H), 2.44 (s, 3 H), 2.31 (m, 1 H), 2.21 (dd, J =
17.0, 4.7 Hz, 1 H), 1.87 (dd, J = 17.0, 9.8 Hz, 1 H), 1.77 (m, 1 H),
1.72 (m, 1 H), 1.40 (m, 1 H), 1.36 (s, 3 H), 1.35 (s, 3 H), 1.28 (m,
3 H), 1.07 (m, 2 H), 0.93 (t, J = 7.9 Hz, 9 H), 0.89 (d, J = 6.3 Hz,
3 H), 0.86 (m, 1 H), 0.60 (d, J = 7.9 Hz, 6 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 144.8 (C), 133.1 (C), 129 (2ϫC=), 128.0
(2ϫC=), 107.8 (CH), 87.3 (C), 80.1 (C), 71.3 (CH2OH), 66.2 (C),
56.7 (OCH3), 56.1 (OCH3), 47.3 (CH), 42.7 (CH), 37.2 (CH), 34.5
(CH), 33.1 (2ϫCH3), 25.6 (CH2), 25.1 (CH2), 24.4 (CH2), 21.6
9.3 (CH ) ppm. IR: ν = 2949 (vs), 2916 (s), 2830 (m), 1737 (vs),
˜
3
1456 (m), 1383 (m), 1244 (m), 1201 (s), 1149 (s), 1132 (s), 1092 (s),
1056 (s), 959 (m) cm–1. MS: m/z (%) = 195 (4), 163 (2), 135 (4),
107 (16), 81 (5), 75 (100), 47 (15), 41 (16).
Representative Procedure for the Reduction with Lithium Aluminum
Hydride of Esters 26 and 40: To a solution of the ester (1.0 equiv.)
in diethyl ether (0.3 ) was added at 0 °C lithium aluminum hydride
(1.5 equiv.). The reaction mixture was stirred for 1 h at room tem-
perature, cooled to 0 °C, and treated successively with water, a so-
dium hydroxide solution (15%), and again with water. The reaction
mixture was further stirred for 1 h at room temperature. After fil-
tration of the white precipitate over Celite, the filtrate was concen-
trated in vacuo. The residue was purified by column chromatog-
raphy with pentane/ethyl acetate (8:2). From ester 26 (0.36 g,
0.8 mmol) was obtained 0.32 g of 28 (94% yield); from ester 40
(0.14 g, 0.31 mmol) 0.12 g of 43 (94% yield).
(CH ), 15.5 (CH ), 15.1 (CH ), 7.0 (CH ), 6.1 (CH ) ppm. IR: ν =
˜
3
3
2
3
2
2932 (m), 1715 (vw), 1598 (vw), 1478 (w), 1365 (s), 1244 (w), 1188
(s), 1176 (vs), 1158 (s), 1069 (s), 1034 (s), 969 (s), 834 (s), 814 (s),
742 (s), 666 (vs) cm–1. MS: m/z (%) = 401 (1), 335 (1), 257 (26),
213 (16), 173 (6), 165 (7), 105 (6), 91 (21), 75 (100), 47 (16). (b)
Step 2: To a solution of tosylate 29 (1.0 equiv.) in tetrahydrofuran
(0.03 ) was added lithium aluminum hydride (4.0 equiv.). After
stirring overnight a saturated solution of sodium sulfate was added,
the mixture was further stirred for 30 min at room temperature,
and the suspension was filtered through a short pad of Celite. After
28: Rf = 0.42 (i-octane/EtOAc, 7:3). [α]D = +1.6 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.33 (d, J = 2.5 Hz, 1 H), 3.82
(ddd, J = 10.7, 6.0, 4.4 Hz, 1 H), 3.56 (dt, J = 10.7, 6.6 Hz, 1 H),
3.44 (s, 3 H), 3.40 (s, 3 H), 2.25 (dd, J = 16.5, 4.4 Hz, 1 H), 2.17
1732
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1720–1737

Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
concentration of the filtrate in vacuo the residue was purified by
column chromatography with pentane/ethyl acetate (87:3) to afford
(m, 1 H), 1.20 (m, 1 H), 1.10 (m, 1 H), 1.02 (m, 2 H), 0.81 (q, J =
12.3 Hz, 1 H), 0.79 (d, J = 6.3 Hz, 3 H), 0.72 (d, J = 7.0 Hz, 3 H)
0.10 g of 30 in 89% yield. Rf = 0.59 (i-octane/EtOAc, 7:3). [α]D
=
ppm. 13C NMR (125 MHz, CDCl3): δ = 144.6 (C=), 133.2 (C=),
1
+2.9 (c = 1.0, CHCl3). H NMR (500 MHz, CDCl3): δ = 4.33 (d, 129.9 (2ϫ=CH), 127.9 (2ϫ=CH), 107.3 (CHO2), 74.4 (CH2O),
J = 2.5 Hz, 1 H), 3.44 (s, 3 H), 3.40 (s, 3 H), 2.19 (dd, J = 16.4, 65.0 (2ϫCH2O), 43.3 (CH), 41.4 (CH), 35.0 (CH2), 33.7 (CH),
3.8 Hz, 1 H), 2.09 (m, 1 H), 1.80 (dd, J = 16.4, 10.1 Hz, 1 H), 1.79 32.6 (CH), 26.7 (CH2), 25.7 (CH2), 21.7 (CH3), 19.4 (CH3), 9.9
(m, 2 H), 1.64 (m, 1 H), 1.44 (s, 6 H), 1.39 (m, 1 H), 1.28 (m, 1
H), 1.14 (m, 2 H), 1.02 (d, J = 6.6 Hz, 3 H), 1.00 (m, 1 H), 0.96
(t, J = 7.9 Hz, 9 H), 0.95 (d, J = 6.0 Hz, 3 H), 0.88 (qd, J = 12.3,
3.2 Hz, 1 H), 0.66 (d, J = 7.9 Hz, 6 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 108.1 (CH), 86.0 (Cϵ), 82.7 (Cϵ), 66.3 (C), 56.8
(OCH3), 56.0 (OCH3), 48.9 (CH), 47.6 (CH), 35.1 (CH), 33.3
(2ϫCH3), 32.4 (CH2), 26.0 (CH2), 25.1 (CH2), 24.5 (CH3), 19.9
(CH ) ppm. IR: ν = 2918 (s), 2876 (s), 1598 (w), 1458 (w), 1360
˜
3
(vs), 1189 (vs), 1178 (vs), 1097 (m), 958 (vs), 845 (vs), 816 (vs) cm–1.
MS: m/z (%) = 336 (3), 21 (3), 155 (5), 149 (4), 136 (3), 107 (5), 91
(21), 81 (10), 73 (100), 45 (15), 41 (6).
Representative Procedure for the Reduction with Lithium Aluminum
Hydride of Esters 27 and 39 and the mixture of 45: To a solution of
the ester (1.0 equiv.) in diethyl ether (0.3 ) was added at 0 °C lith-
ium aluminum hydride (1.5 equiv.). The resulting reaction mixture
was stirred for 1 h at room temperature, cooled (0 °C), and treated
successively with water, aqueous solution of sodium hydroxide
(15%), and water again. After further stirring for 1 h at room tem-
perature the white precipitate was filtered through Celite and the
filtrate was concentrated in vacuo. The residue was purified by col-
umn chromatography with pentane/ethyl acetate (8:2). From ester
27 (0.74 g, 2.86 mmol) was obtained 0.625 g of alcohol 33 (95%
yield); from ester 39 (100 mg, 0.39 mmol) 85 mg of 41 (85% yield).
In the case of 45 (0.80 g) a 1:1 mixture of alcohols 46a and 15 was
obtained (584 mg, 82% yield).
(CH ), 18.9 (CH ), 15.7 (CH ), 7.0 (CH ), 6.3 (CH ) ppm. IR: ν =
˜
2
3
3
3
2
2931 (m), 2874 (m), 1458 (m), 1375 (m), 1245 (m), 1157 (vs), 1114
(m), 1073 (s), 1034 (vs), 961 (m), 904 (w), 768 (m), 741 (vs), 725
(vs) cm–1. MS: m/z (%) = 363 (2), 349 (2), 291 (1), 249 (1), 233 (3),
205 (6), 175 (18), 147 (7), 117 (23), 105 (10), 75 (100), 47 (13).
Step 3: To a solution of alkyne 30 (1.0 equiv.) in ethyl acetate
(0.1 ) was added molecular sieves (3.0 equiv.) and platinum oxide
(5 mol-%). The flask was flushed with hydrogen and the mixture
stirred overnight under an atmosphere of hydrogen. After comple-
tion of the reaction (TLC development with anisaldehyde) the reac-
tion mixture was filtered through Celite. After concentration of the
filtrate in vacuo the residue was purified by HPLC with isooctane/
ethyl acetate (96:4) to afford 0.1 g of 31 (98% yield). In the same
way, alcohol 43 (0.06 g, 0.14 mmol) was converted into 0.045 g of
compound 44 in 80% overall yield.
33: Rf = 0.45 (i-octane/EtOAc, 3:7). [α]D = –5.0 (c = 1.87, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.34 (d, J = 2.5 Hz, 1 H), 3.49
(m, 2 H), 3.44 (s, 3 H), 3.39 (s, 3 H), 2.04 (m, 1 H), 1.80 (m, 2 H),
1.45 (m, 1 H), 1.37 (m, 1 H), 1.32 (s, 1 H), 1.30 (m, 1 H), 1.22 (m,
1 H), 1.14 (m, 2 H), 1.00 (qd, J = 12.3, 2.5 Hz, 1 H), 0.93 (d, J =
6.0 Hz, 3 H), 0.76 (d, J = 6.9 Hz, 3 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 108.1 (CH), 76.3 (CH2OH), 56.8 (OCH3), 56.0
(OCH3), 47.4 (CH), 43.9 (CH), 35.3 (CH), 34.6 (CH), 25.7 (CH2),
31: Rf = 0.62 (i-octane/EtOAc, 7:3). [α]D = +6.0 (c = 1.0, CHCl3).
1HNMR (500 MHz, CDCl3): δ = 4.34 (d, J = 2.8 Hz, 1 H), 3.45
(s, 3 H), 3.40 (s, 3 H), 1.80 (m, 3 H), 1.62 (m, 1 H), 1.44 (m, 2 H),
1.40 (m, 1 H), 1.35 (m, 1 H), 1.28 (m, 2 H), 1.18 (s, 6 H), 1.15 (m,
1 H), 1.14 (m, 2 H), 0.94 (t, J = 7.9 Hz, 9 H), 0.91 (d, J = 6.6 Hz, 24.8 (CH ), 24.5 (CH ), 15.5 (CH ), 10.2 (CH ) ppm. IR: ν = 3409
˜
2
2
3
3
3 H), 0.89 (d, J = 6.9 Hz, 3 H), 0.89 (m, 3 H), 0.66 (d, J = 7.9 Hz,
(br. s), 2929 (vs), 2873 (s), 1448 (m), 1375 (m), 1305 (vw), 1170 (m),
6 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 108.2 (CH), 73.2 (C),
1122 (m), 1072 (vs), 1044 (s), 958 (m), 913 (w), 851 (w) cm–1. MS:
56.8 (OCH3), 56.0 (OCH3), 47.6 (CH), 45.4 (CH2), 34.9 (CH), 32.2 m/z (%) = 149 (2), 121 (2), 109 (3), 95 (3), 81 (6), 75 (100), 67 (8),
(CH), 30.4 (CH2), 30.0 (CH3), 29.9 (CH3), 26.2 (CH2), 25.3 (CH2), 47 (16), 41 (14). C14H26O4 (258.35): calcd. C 67.79, H 11.38; found
24.7 (CH2), 23.0 (CH3), 18.7 (CH3), 15.7 (CH3), 7.1 (CH3), 6.8
C 67.80, H 12.11.
(CH ) ppm. IR: ν = 2931 (s), 2847 (m), 1459 (m), 1377 (m), 1364
˜
2
41: Rf = 0.33 (i-octane/EtOAc, 5:5). [α]D = –20.9 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.03 (d, J = 6.7 Hz, 1 H), 3.56
(m, 2 H), 3.38 (s, 3 H), 3.37 (s, 3 H), 2.06 (sxd, J = 7.2, 2.9 Hz, 1
H), 1.78 (m, 2 H), 1.66 (m, 1 H), 1.58 (m, 1 H), 1.40 (t, J = 4.6 Hz,
1 H), 1.29 (m, 1 H), 1.22 (tt, J = 11.6, 3.0 Hz, 1 H), 1.06 (m, 2 H),
0.92 (d, J = 6.4 Hz, 3 H), 0.83 (q, J = 12.1 Hz, 1 H), 0.81 (d, J =
6.9 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 108.8 (CH),
67.0 (CH2OH), 54.0 (OCH3), 53.6 (OCH3), 43.6 (CH), 40.3 (CH),
35.6 (CH), 35.4 (CH2), 33.8 (CH), 27.9 (CH2), 26.3 (CH2), 19.6
(m), 1233 (m), 1212 (m), 1159 (m), 1123 (m), 1073 (vs), 1042 (vs),
1016 (s), 961 (s), 741 (vs), 721 (vs) cm–1. MS: m/z (%) = 382 (1),
353 (2), 219 (2), 173 (17), 163 (7), 135 (5), 103 (15), 75 (100), 69
(11), 47 (11).
44: Rf = 0.56 (i-octane/EtOAc, 9:1). [α]D = –21.9 (c = 0.75, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.98 (d, J = 7.0 Hz, 1 H), 3.34
(s, 3 H), 3.33 (s, 3 H), 1.76 (m, 1 H), 1.72 (m, 3 H), 1.57 (m, 1 H),
1.44 (m, 2 H), 1.32 (m, 1 H), 1.25 (m, 2 H), 1.19 (m, 1 H), 1.17 (s,
6 H), 0.99 (m, 2 H), 0.90 (d, J = 6.9 Hz, 3 H), 0.89 (m, 1 H), 0.85
(CH ), 10.2 (CH ) ppm. IR: ν = 3421 (br. s, m), 2950 (vs), 2917
˜
3
3
(m, 12 H), 0.70 (q, J = 12.2 Hz, 1 H), 0.05 (s, 6 H) ppm. 13C NMR (vs), 2874 (vs), 1455 (m), 1380 (m), 1193 (m), 1129 (vs), 1096 (vs),
(125 MHz, CDCl3): δ = 108.9 (CH), 73.6 (COH), 53.9 (OCH3),
53.6 (OCH3), 49.8 (CH), 45.5 (CH2), 40.7 (CH), 35.8 (CH2), 34.1
(CH2), 32.8 (CH), 30.9 (CH2), 30.0 (CH3), 29.9 (CH3), 28.2 (CH2),
27.2 (CH2), 25.9 (3ϫCH3), 23.0 (CH2), 20.0 (CH3), 18.5 (CH3),
1059 (vs), 957 (s), 984 (m), 957 (m), 756 (m) cm–1. MS: m/z (%) =
107 (5), 93 (5), 81 (5), 75 (100), 55 (15), 41 (16).
46a: Rf = 0.31 (i-octane/EtOAc, 1:1). [α]D = +10.3 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.99 (d, J = 6.9 Hz, 1 H), 3.64
(dt, J = 10.7, 4.3 Hz, 1 H), 3.46 (dt, J = 10.7, 5.6 Hz, 1 H), 3.33
(s, 3 H), 3.32 (s, 3 H), 1.95 (m, 1 H), 1.64 (m, 1 H), 1.58 (m, 2 H),
1.47 (m, 3 H), 1.31 (m, 1 H), 1.16 (m, 1 H), 0.96 (d, J = 6.9 Hz, 3
H), 0.88 (m, 1 H), 0.83 (d, J = 7.3 Hz, 3 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 108.8 (CH), 66.1 (CH2OH), 54.0 (OCH3),
53.6 (OCH3), 41.5 (CH), 41.0 (CH), 37.5 (CH), 33.1 (CH2), 29.2
18.2 (CSi), –2.0 (2ϫSiCH ) ppm. IR: ν = 2951 (s), 2926 (s), 2854
˜
3
(m), 1461 (m), 1380 (m), 1363 (m), 1251 (s), 1211 (m), 1169 (m),
1130 (s), 1053 (vs), 1005 (m), 955 (m), 864 (w), 833 (vs), 770 (vs),
689 (m) cm–1. MS: m/z (%) = 251 (1), 219 (3), 173 (15), 163 (8),
135 (2), 107 (10), 95 (11), 75 (100), 55 (8), 41 (7).
14: Rf = 0.46 (i-octane/EtOAc, 5:5). M.p. 93 °C. 1H NMR
(500 MHz, CDCl3): δ = 7.78 (d, J = 8.2 Hz, 2 H), 7.34 (d, J =
8.2 Hz, 2 H), 4.51 (d, J = 4.7 Hz, 1 H), 3.89 (m, 4 H), 3.83 (m, 2
H), 2.44 (s, 3 H), 2.17 (m, 1 H), 1.72 (m, 2 H), 1.46 (m, 1 H), 1.31
(CH), 24.9 (CH ), 21.7 (CH ), 15.3 (CH ), 12.4 (CH ) ppm. IR: ν
˜
2
2
3
3
= 3418 (m), 2928 (vs), 2830 (m), 1458 (m), 1442 (m), 1382 (m),
1189 (m), 1126 (s), 1088 (s), 1054 (vs), 985 (m), 962 (m), 756 (m)
Eur. J. Org. Chem. 2009, 1720–1737
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1733

P. De Clercq et al.
FULL PAPER
cm–1. MS: m/z (%) = 149 (3), 107 (4), 93 (4), 75 (100), 55 (9), 47
(14).
J = 6.3 Hz, 3 H), 0.85 (d, J = 6.9 Hz, 3 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 141.3 (=CH), 123.3 (=CH), 108.1 (CH),
70.4 (C), 56.8 (OCH3), 56.0 (OCH3), 48.7 (CH), 47.4 (CH), 47.1
(CH2), 35.6 (CH), 34.9 (CH), 29.0 (2ϫCH2), 25.9 (CH2), 25.4
15: Rf = 0.23 (i-octane/EtOAc: 1:1). M.p. 66 °C. [α]D = +7.4 (c =
1.0, CHCl3). 1H NMR (500 MHz, CDCl3): δ = 3.98 (d, J = 6.9 Hz,
1 H), 3.70 (dt, J = 10.2, 4.2 Hz, 1 H), 3.52 (dt, J = 10.2, 5.7 Hz, 1
H), 3.33 (s, 3 H), 3.32 (s, 3 H), 1.98 (m, 1 H), 1.67 (m, 1 H), 1.61
(m, 1 H), 1.56 (m, 1 H), 1.50 (m, 1 H), 1.45 (m, 1 H), 1.38 (m, 1
H), 1.27 (m, 1 H), 1.18 (qd, J = 12.3, 3.5 Hz, 1 H), 0.97 (d, J =
6.6 Hz, 3 H), 0.89 (qd, J = 12.6, 3.1 Hz, 1 H), 0.80 (d, J = 6.9 Hz,
3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 108.8 (CH), 66.4
(CH2OH), 54.1 (OCH3), 53.6 (OCH3), 41.2 (CH), 40.7 (CH), 38.5
(CH), 33.0 (CH2), 28.3 (CH), 25.4 (CH2), 21.6 (CH2), 14.9 (CH3),
(CH ), 24.6 (CH ), 14.6 (CH ), 11.1 (CH ) ppm. IR: ν = 3416 (br.
˜
2
2
3
3
w), 2967 (m), 2929 (m), 1448 (m), 1374 (m), 1202 (m), 1155 (m),
1118 (s), 1068 (vs), 961 (s), 905 (m), 753 (vs), 666 (w) cm–1. MS:
m/z (%) = 208 (3), 161 (3), 147 (1), 139 (3), 107 (10), 93 (6), 75
(100), 59 (41), 41 (13).
Step 3: To a solution of alkene 36 (1.0 equiv.) in ethyl acetate
(0.1 ) was added molecular sieves (3.0 equiv.) and rhodium/C. The
flask was flushed with hydrogen, and the mixture was stirred over-
night under an atmosphere of hydrogen. The mixture was filtered
through Celite and the filtrate concentrated in vacuo to afford
217 mg of compound 37 in quantitative yield. In the same way
starting from alcohol 41 (95 mg, 0.412 mmol) was obtained inter-
mediate 42 (78 mg, 63% overall yield), from alcohol 46a (67 mg,
0.29 mmol) intermediate 47a (55 mg, 63% overall yield), and from
alcohol 15 (70 mg, 0.304 mmol) intermediate 47b (60 mg, 66%
overall yield).
11.8 (CH ) ppm. IR: ν = 3418 (m), 2925 (vs), 2831 (m), 1465 (m),
˜
3
1442 (m), 1389 (m), 1188 (m), 1129 (s), 1086 (s), 1054 (vs), 988 (m),
853 (m) cm–1. MS: m/z (%) = 149 (3), 107 (5), 93 (6), 75 (100), 67
(9), 47 (19).
The Three-Step Synthesis of Intermediates 37, 42, 47a, and 47b
Step 1: To a solution of oxalyl chloride (1.1 equiv.) in dichloro-
methane (0.3 ) was added at –78 °C dropwise a solution of di-
methyl sulfoxide (2.2 equiv.) in dichloromethane (3 ), followed by
a solution of alcohol 33 (1 equiv., 200 mg, 0.686 mmol) in dichloro-
methane (0.5 ). After stirring for 15 min at –78 °C triethylamine
(5 equiv.) was added, and the reaction mixture was slowly brought
to room temperature. After addition of water and tert-butyl methyl
ether the mixture was partly concentrated in vacuo. The organic
phase obtained after the addition of tert-butyl methyl ether was
washed with water, dried (magnesium sulfate), and concentrated in
vacuo. The residue was purified by column chromatography with
pentane/ethyl acetate (9:1) to afford pure aldehyde 34. Rf = 0.60
(i-octane/EtOAc, 3:7). [α]D = –64.8 (c = 1.0, CHCl3). 1H NMR
(500 MHz, CDCl3): δ = 9.65 (s, 1 H), 4.33 (d, J = 2.5 Hz, 1 H),
3.44 (s, 3 H), 3.40 (s, 3 H), 2.66 (qd, J = 6.9, 3.2 Hz, 1 H), 1.81 (m,
1 H), 1.76 (m, 1 H), 1.71 (m, 1 H), 1.41 (m, 2 H), 1.22 (m, 2 H),
1.15 (m, 1 H), 1.10 (m, 1 H), 0.96 (d, J = 6.9 Hz, 3 H), 0.96 (d, J
= 6.0 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 206.2
(CHO), 107.9 (CH), 56.7 (OCH3), 56.2 (OCH3), 47.4 (CH), 47.3
(CH), 43.2 (CH), 34.4 (CH), 26.9 (CH2), 25.5 (CH2), 24.6 (CH2),
37: Rf = 0.44 (i-octane/EtOAc, 1:1). [α]D = –9.7 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.33 (d, J = 2.5 Hz, 1 H), 3.44
(s, 3 H), 3.39 (s, 3 H), 1.79 (m, 3 H), 1.51 (m, 1 H), 1.44 (m, 2 H),
1.32 (m, 4 H), 1.21 (s, 6 H), 1.20 (m, 1 H), 1.13 (m, 2 H), 0.99 (m,
1 H), 0.95 (m, 1 H), 0.90 (d, J = 6.6 Hz, 3 H), 0.72 (d, J = 6.6 Hz,
3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 108.1 (CH), 71.0 (C),
56.8 (OCH3), 56.0 (OCH3), 47.5 (CH), 47.2 (CH), 44.3 (CH2), 36.3
(CH2), 34.9 (CH), 32.1 (CH), 29.3 (2ϫCH2), 26.0 (CH2), 24.6
(CH ), 24.5 (CH ), 22.6 (CH ), 15.5 (CH ), 13.4 (CH ) ppm. IR: ν
˜
2
2
2
3
3
= 3421 (br. w), 2961 (m), 2931 (m), 1462 (m), 1448 (m), 1378 (m),
1201 (m), 1164 (m), 1119 (m), 1069 (s), 959 (m), 945 (m), 752 (vs),
666 (m) cm–1. MS: m/z (%) = 221 (2), 203 (2), 163 (1), 149 (2), 149
(2), 109 (4), 95 (7), 75 (100), 59 (20), 41 (10).
42: Rf = 0.40 (i-octane/EtOAc, 1:1). [α]D = –13.5 (c = 1.0, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.98 (d, J = 6.6 Hz, 1 H), 3.33
(s, 6 H), 1.74 (m, 3 H), 1.61 (m, 1 H), 1.58 (m, 1 H), 1.45 (t, J =
7.3 Hz, 2 H), 1.35 (m, 2 H), 1.23 (m, 3 H), 1.21 (s, 6 H), 0.94 (m,
1 H), 0.85 (d, J = 6.3 Hz, 3 H), 0.73 (d, J = 6.9 Hz, 3 H), 0.72 (m,
1 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 108.8 (CH), 71.1 (C),
53.6 (2ϫOCH3), 47.1 (CH), 44.3 (CH2), 40.4 (CH), 36.0 (CH2),
35.5 (CH2), 34.1 (CH), 32.4 (CH), 29.3 (2ϫCH3), 28.0 (CH2), 26.1
15.7 (CH ), 6.5 (CH ) ppm. IR: ν = 2979 (vs), 2936 (vs), 2872 (s),
˜
3
3
2722 (vw), 1721 (vs), 1618 (vw), 1451 (m), 1403 (m), 1378 (m), 1327
(w), 1301 (w), 1256 (w), 1223 (m), 1171 (m), 1127 (s), 1070 (vs),
989 (m), 950 (s), 909 (w), 654 (w) cm–1. MS: m/z (%) = 107 (6), 95
(6), 81 (4), 75 (100), 67 (6), 55 (9), 41 (10).
(CH ), 22.6 (CH ), 19.7 (CH ), 13.4 (CH ) ppm. IR: ν = 3425 (w),
˜
2
2
3
3
2929 (s), 2868 (m), 1455 (m), 1378 (m), 1362 (m), 1192 (m), 1152
(m), 1132 (s), 1096 (s), 1053 (vs), 981 (m), 955 (s), 936 (m), 903
(m), 765 (vw) cm–1. MS: m/z (%) = 221 (1), 203 (1), 165 (4), 149
(1), 137 (2), 123 (2), 107 (4), 95 (4), 81 (3), 75 (100), 59 (14), 45 (4).
Step 2: To a solution of phosphonium bromide 35 (2.0 equiv.) in
tetrahydrofuran (0.25 ) was added at –20 °C dropwise a solution
of methyllithium (4 equiv.) in diethyl ether (1.6 ). The reaction
mixture was further stirred for 1 h at –20 °C and for 3 h at room
temperature. The red-colored solution of the ylide was treated at
–40 °C with a solution of aldehyde 34 (0.2 , 1 equiv.). The reaction
mixture was slowly brought to room temperature and further
stirred for 1 h. After addition of water and extraction with tert-
butyl methyl ether, the organic phase was dried (magnesium sulfate)
and concentrated in vacuo. The residue was treated with silica gel
(by successive addition of dichloromethane and concentration),
and the obtained solid phase was purified by column chromatog-
raphy with pentane/ethyl acetate (93:7). Pure alkene 36 (218 mg,
84% yield) was obtained by further HPLC with isooctane/ethyl
acetate (8:2). Rf = 0.45 (i-octane/EtOAc, 1:1). [α]D = –23.7 (c = 1.0,
CHCl3). 1H NMR (500 MHz, CDCl3): δ = 5.55 (dd, J = 15.5,
6.0 Hz, 1 H), 5.42 (dt, J = 15.5, 7.3 Hz, 1 H), 4.33 (d, J = 2.2 Hz,
1 H), 3.44 (s, 3 H), 3.39 (s, 3 H), 2.58 (m, 1 H), 2.17 (d, J = 7.3 Hz,
2 H), 1.78 (m, 2 H), 1.52 (m, 1 H), 1.36 (m, 1 H), 1.30 (m, 1 H),
1.19 (s, 6 H), 1.13 (m, 2 H), 1.06 (m, 1 H), 0.97 (m, 1 H), 0.94 (d,
47a: Rf = 0.45 (i-octane/EtOAc, 1:1). [α]D = +25.3 (c = 1.5, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 3.98 (d, J = 6.9 Hz, 1 H), 3.33
(s, 3 H), 3.31 (s, 3 H), 1.98 (m, 1 H), 1.65 (m, 1 H), 1.61 (m, 2 H),
1.51 (m, 2 H), 1.45 (m, 4 H), 1.29 (m, 2 H), 1.25 (s, 6 H), 1.17 (m,
2 H), 1.09 (m, 1 H), 0.91 (d, J = 6.6 Hz, 3 H), 0.87 (q, J = 12.6 Hz,
1 H), 0.83 (d, J = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3):
δ = 108.8 (CH), 71.1 (C), 53.8 (OCH3), 53.5 (OCH3), 44.8 (CH),
44.4 (CH2), 40.8 (CH), 34.5 (CH), 34.1 (CH2), 33.2 (CH2), 29.3
(CH3), 29.2 (CH3), 28.2 (CH), 25.3 (CH2), 21.7 (CH2), 21.1 (CH2),
17.4 (CH ), 12.2 (CH ) ppm. IR: ν = 3438 (m), 2964 (vs), 2936
˜
3
3
(vs), 1466 (m), 1445 (m), 1379 (m), 1189 (m), 1155 (m), 1130 (m),
1075 (m), 1054 (s), 953 (m), 757 (vs) cm–1. MS: m/z (%) = 268 (9),
250 (16), 235 (3), 203 (3), 165 (100), 137 (22), 123 (10), 107 (35),
85 (38), 79 (25), 59 (48), 55 (50), 41 (59).
47b: Rf = 0.45 (i-octane/EtOAc, 1:1). [α]D = –11.2 (c = 0.9, CHCl3).
1H NMR (500 MHz, CDCl3): δ = 4.00 (d, J = 6.9 Hz, 1 H), 3.34
1734
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1720–1737

Analogues of 1α,25-Dihydroxyvitamin D3 with Biased Side-Chain Orientation
(s, 3 H), 3.33 (s, 3 H), 2.00 (m, 1 H), 1.70 (m, 1 H), 1.60 (m, 1 H),
1.55 (m, 1 H), 1.47 (m, 4 H), 1.42 (m, 2 H), 1.23 (m, 2 H), 1.21 (s,
6 H), 1.19 (m, 1 H), 1.05 (m, 2 H), 0.86 (d, J = 6.3 Hz, 3 H), 0.83
(q, J = 12.6 Hz, 1 H), 0.78 (d, J = 7.3 Hz, 3 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 108.8 (CH), 71.1 (C), 53.7 (OCH3), 53.6
(OCH3), 44.8 (CH), 44.4 (CH2), 40.8 (CH), 34.9 (CH), 34.7 (CH2),
33.2 (CH2), 29.3 (CH3), 29.2 (CH3), 28.7 (CH), 25.3 (CH2), 21.8
1028 (vs), 976 (vs), 959 (m), 911 (s), 928 (vs), 877 (w), 756 (w), 736
(vs) cm–1. MS: m/z (%) = 372 (7), 336 (3), 243 (1), 207 (1), 164 (14),
148 (50), 131 (36), 105 (25), 95 (42), 59 (100), 49 (34).
1
5b: Rf = 0.74 (acetone). [α]D = +24.9 (c = 1.0, CHCl3). H NMR
(500 MHz, CDCl3): δ = 6.33 (dd, J = 15.1, 10.7 Hz, 1 H), 6.03 (d,
J = 10.7 Hz, 1 H), 5.53 (dd, J = 15.1, 8.8 Hz, 1 H), 5.30 (s, 1 H),
4.99 (s, 1 H), 4.43 (m, 1 H), 4.21 (m, 1 H), 2.57 (d, J = 12.9 Hz, 1
H), 2.25 (dd, J = 12.9, 7.5 Hz, 1 H), 1.96 (m, 2 H), 1.78 (m, 1 H),
1.74 (m, 1 H), 1.64 (m, 4 H), 1.53 (m, 1 H), 1.44 (t, J = 8.1 Hz, 2
H), 1.32 (m, 2 H), 1.24 (m, 1 H), 1.21 (s, 6 H), 1.19 (m, 1 H), 1.08
(m, 2 H), 0.97 (m, 2 H), 0.80 (d, J = 6.3 Hz, 3 H), 0.72 (d, J =
6.9 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 147.4 (C=),
141.1 (=CH), 133.2 (C=), 129.7 (=CH), 126.0 (=CH), 112.2
(=CH2), 71.2 (CHOH), 71.1 (C), 66.7 (CHOH), 49.3 (CH), 46.9
(CH), 45.1 (CH2), 44.2 (CH2), 42.8 (CH2), 38.6 (CH), 36.2 (CH2),
34.0 (CH2), 32.2 (CH), 29.3 (CH3), 29.2 (CH3), 26.0 (CH2), 24.5
(CH ), 21.5 (CH ), 16.8 (CH ), 11.9 (CH ) ppm. IR: ν = 3436 (w),
˜
2
2
3
3
2963 (s), 2933 (s), 2906 (s), 2829 (w), 1465 (m), 1442 (m), 1376 (m),
1188 (m), 1147 (s), 1128 (vs), 1075 (s), 1052 (vs), 986 (m), 961 (m),
937 (m), 906 (m), 755 (vs), 665 (w) cm–1. MS: m/z (%) = 243 (1),
213 (15), 199 (39), 181 (15), 171 (7), 153 (19), 141 (12), 125 (6), 103
(100), 91 (40), 75 (88), 59 (22), 45 (42), 41 (27).
Synthesis of Analogues 5a, 5b, 6a, 6b, 7a, and 7b
Step 1: To a solution of the acetal (1.0 equiv.) in dichloromethane
(0.1 ) was added at 0 °C 2,4,6-collidine (4 equiv.) followed by tri-
ethylsilyl trifluoromethanesulfonate (3.0 equiv.). After stirring the
reaction mixture for 1 h at 0 °C, water was added and after further
stirring for 30 min at room temperature the mixture was extracted
with dichloromethane. The organic phase was dried (magnesium
sulfate) and concentrated in vacuo. The residue was purified by
column chromatography with pentane/ethyl acetate (98:2) to afford
the corresponding aldehyde.
(CH ), 22.5 (CH ), 17.0 (CH ), 13.4 (CH ) ppm. IR: ν = 3354 (s),
˜
2
2
3
3
2961 (s), 2924 (vs), 2853 (s), 1721 (vw), 1628 (vw), 1445 (m), 1377
(m), 1300 (m), 1212 (m), 1168 (m), 1150 (m), 1054 (s), 975 (m), 959
(m), 912 (m), 737 (m) cm–1. MS: m/z (%) = 336 (14), 318 (4), 292
(3), 260 (4), 253 (11), 212 (4), 193 (8), 165 (5), 151 (18), 129 (100),
95 (52), 59 (52), 41 (22).
6a: Rf = 0.70 (acetone). 1H NMR (500 MHz, CDCl3): δ = 6.37 (dd,
J = 15.2, 10.8 Hz, 1 H), 6.02 (d, J = 10.8 Hz, 1 H), 5.66 (dd, J =
15.2, 7.2 Hz, 1 H), 5.31 (s, 1 H), 5.01 (s, 1 H), 4.43 (m, 1 H), 4.21
(m, 1 H), 2.56 (dd, J = 13.2, 1.8 Hz, 1 H), 2.26 (dd, J = 13.2,
6.8 Hz, 1 H), 1.97 (m, 3 H), 1.76 (m, 1 H), 1.69 (m, 2 H), 1.59 (s,
1 H), 1.54 (s, 1 H), 1.52 (m, 1 H), 1.45 (m, 2 H), 1.33 (m, 2 H),
1.22 (m, 9 H), 1.05 (m, 2 H), 0.99 (m, 1 H), 0.85 (d, J = 6.2 Hz, 3
H), 0.79 (q, J = 12.3 Hz, 1 H), 0.72 (d, J = 6.8 Hz, 3 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 147.5 (C=), 141.1 (=CH), 133.6
(C=), 129.7 (=CH), 124.1 (=CH), 111.9 (=CH2), 71.1 (C), 71.0
(CHOH), 66.8 (CHOH), 47.2 (CH), 45.0 (CH2), 44.2 (CH2), 42.8
(CH2), 41.5 (CH), 36.0 (CH2), 35.8 (CH2), 33.8 (CH), 32.8 (CH2),
32.3 (CH), 31.3 (CH2), 29.3 (CH3), 29.2 (CH3), 22.6 (CH2), 19.7
Step 2: To a solution resulting from the treatment of phosphane
oxide 32 (2.2 equiv.) with n-butyllithium (2.5  in hexane,
2.15 equiv.) in tetrahydrofuran (0.1 ) was added at –78 °C a solu-
tion of the aldehyde (1.0 equiv.) in tetrahydrofuran (0.15 ). After
stirring of the reaction mixture at –78 °C for 90 min, the mixture
was very slowly brought to 0 °C. After addition of water and ex-
traction with tert-butyl methyl ether the organic phase was dried
(magnesium sulfate) and concentrated in vacuo. The residue con-
taining the protected analogue was further separated from the ex-
cess amount of phosphane oxide by column chromatography with
pentane/ethyl acetate (98.5:1.5).
Step 3: To the above-obtained silyl ether was added a solution of
tetrabutylammonium fluoride (1  solution, 10 equiv.) in tetra-
hydrofuran. After overnight stirring at room temperature the reac-
tion mixture was directly brought on a column and eluted with
dichloromethane/acetone (6:4). The product was further purified
by HPLC with dichloromethane/acetone (75:25). From acetal 31
(11 mg, 0.03 mmol) was obtained 10 mg of analogue 5a (71%
yield), from acetal 37 (10 mg, 0.033 mmol) 10 mg of analogue 5b
(76%), from acetal 42 (13 mg, 0.04 mmol) 12 mg of analogue 6a
(76% yield), from acetal 44 (25 mg, 0.083 mmol) 10 mg of analogue
6b (33% yield), from acetal 47a (18 mg, 0.06 mmol) 9.5 mg of ana-
logue 7a (43% yield), and from acetal 47b (15 mg, 0.05 mmol)
13 mg of analogue 7b (70% yield).
5a: Rf = 0.69 (acetone). 1H NMR (500 MHz, CDCl3): δ = 6.33 (dd,
J = 15.2, 10.7 Hz, 1 H), 6.03 (d, J = 10.7 Hz, 1 H), 5.52 (dd, J =
15.2, 8.9 Hz, 1 H), 5.30 (s, 1 H), 4.99 (s, 1 H), 4.43 (dd, J = 5.4,
5.0 Hz, 1 H), 4.21 (m, 1 H), 2.57 (dd, J = 13.2, 3.8 Hz, 1 H), 2.26
(dd, J = 13.2, 7.6 Hz, 1 H), 1.96 (m, 2 H), 1.80 (m, 1 H), 1.74 (m,
1 H), 1.62 (m, 3 H), 1.59 (s, 1 H), 1.47 (m, 2 H), 1.38 (m, 1 H),
1.28 (m, 1 H), 1.21 (s, 6 H), 1.16 (m, 2 H), 1.11 (m, 2 H), 0.92 (m,
3 H), 0.89 (d, J = 6.9 Hz, 3 H), 0.81 (d, J = 6.3 Hz, 3 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 147.4 (C=), 141.1 (=CH), 133.2
(C=), 129.7 (=CH), 126.1 (=CH), 112.2 (=CH2), 71.2 (CHOH),
71.1 (C), 66.7 (CHOH), 49.8 (CH), 49.4 (CH), 45.1 (CH2), 44.3
(CH ), 13.4 (CH ) ppm. IR: ν = 3288 (m), 2925 (s), 2849 (m), 2161
˜
3
3
(vw), 1979 (vw), 1636 (w), 1445 (m), 1376 (s), 1305 (m), 1245 (m),
1214 (m), 1166 (m), 1155 (m), 1047 (vs), 1034 (vs), 971 (s), 959 (vs),
912 (vs), 893 (m), 737 (s), 668 (s) cm–1. MS: m/z (%) = 372 (7), 354
(3), 259 (3), 241 (2), 223 (2), 187 (1), 164 (11), 133 (19), 105 (15),
91 (25), 59 (100), 43 (39).
6b: Rf = 0.25 (i-octane/EtOAc, 1:1). UV (MeOH): λ = 205, 249 nm.
1H NMR (500 MHz, CDCl3): δ = 6.37 (dd, J = 15.1, 10.9 Hz, 1
H), 6.02 (d, J = 10.9 Hz, 1 H), 5.65 (dd, J = 15.1, 7.1 Hz, 1 H),
5.31 (s, 1 H), 5.01 (s, 1 H), 4.43 (m, 1 H), 4.21 (m, 1 H), 2.66 (dd,
J = 13.3, 3.5 Hz, 1 H), 2.26 (dd, J = 13.3, 7.0 Hz, 1 H), 1.96 (m, 3
H), 1.76 (m, 1 H), 1.69 (m, 2 H), 1.62 (m, 1 H), 1.43 (m, 3 H), 1.29
(m, 9 H), 1.05 (m, 2 H), 0.91 (m, 1 H), 0.89 (d, J = 7.3 Hz, 3 H),
0.86 (d, J = 6.4 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ =
147.6 (C=), 141.4 (=CH), 133.7 (C=), 129.8 (=CH), 124.2 (=CH),
112.0 (=CH2), 71.2 (C), 71.1 (CHOH), 66.8 (CHOH), 50.0 (CH),
45.1 (CH2), 44.3 (CH2), 42.9 (CH2), 41.7 (CH), 36.0 (CH2), 33.7
(CH), 32.9 (CH2), 32.5 (CH), 32.3 (CH2), 30.7 (CH2), 29.3 (CH3),
29.2 (CH ), 20.1 (CH ), 20.0 (CH ), 18.4 (CH ) ppm. IR: ν = 3349
˜
3
2
3
3
(s), 2920 (vs), 2868 (s), 1454 (m), 1370 (m), 1305 (w), 1269 (w),
1207 (w), 1150 (w), 1055 (s), 975 (m), 961 (m), 915 (m), 736 (m)
cm–1. MS: m/z (%) = 372 (2), 336 (10), 288 (3), 232 (4), 202 (2),
149 (14), 129 (77), 91 (58), 59 (100).
1
(CH2), 42.8 (CH2), 38.5 (CH), 34.1 (CH2), 32.4 (CH), 30.5 (CH2), 7a: Rf = 0.40 (EtOAc). H NMR (500 MHz, CDCl3): δ = 6.36 (dd,
29.3 (CH3), 29.2 (CH3), 26.2 (CH2), 25.4 (CH2), 22.9 (CH2), 18.6
(CH ), 17.3 (CH ) ppm. IR: ν = 3349 (s), 2931 (vs), 2862 (s), 1455
J = 15.4, 10.8 Hz, 1 H), 6.02 (d, J = 10.8 Hz, 1 H), 5.66 (dd, J =
15.4, 7.0 Hz, 1 H), 5.31 (s, 1 H), 5.01 (s, 1 H), 4.43 (m, 1 H), 4.21
˜
3
3
(m), 1377 (s), 1306 (m), 1208 (m), 1139 (m), 1101 (m), 1053 (vs), (m, 1 H), 2.56 (dd, J = 13.3, 3.7 Hz, 1 H), 2.26 (dd, J = 13.3,
Eur. J. Org. Chem. 2009, 1720–1737
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1735

P. De Clercq et al.
FULL PAPER
7.0 Hz, 1 H), 1.99 (m, 1 H), 1.96 (m, 2 H), 1.92 (m, 1 H), 1.56 (m,
2 H), 1.54 (d, J = 4.9 Hz, 1 H), 1.50 (d, J = 5.3 Hz, 1 H), 1.42 (m,
6 H), 1.25 (m, 3 H), 1.21 (s, 6 H), 1.15 (m, 1 H), 1.05 (m, 1 H),
their ability to compete with [3H]1,25(OH)2D3 for binding to high-
speed supernatant from intestinal mucosa homogenates obtained
from normal pigs as described previously.[30] The relative affinity
0.90 (q, J = 12.5 Hz, 1 H), 0.85 (d, J = 6.6 Hz, 3 H), 0.79 (d, J = of the analogues was calculated from their concentration needed to
7.0 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 147.6 (C=), displace 50% of [3H]1,25(OH)2D3 from its receptor compared with
141.5 (=CH), 133.6 (C=), 129.8 (=CH), 124.1 (=CH), 112.0 the activity of 1,25(OH)2D3.
(=CH2), 71.1 (CHOH), 71.0 (C), 66.8 (CHOH), 45.1 (CH2), 45.0
Biological Evaluation – MCF-7 Proliferation Assay: The human
(CH), 44.4 (CH2), 42.9 (CH2), 41.9 (CH), 34.4 (CH), 34.1 (CH2),
breast carcinoma (MCF-7) cell line was obtained from the Ameri-
33.5 (CH2), 30.6 (CH2), 29.4 (CH3), 29.3 (CH3), 28.6 (CH), 26.6
can Tissue Culture Company (Rockville, MD). The antiprolifera-
(CH2), 21.1 (CH2), 17.4 (CH3), 12.3 (CH3) ppm.
tive activity of 1,25(OH)2D3 or 6D analogues on MCF-7 cells was
1
7b: Rf = 0.40 (EtOAc). UV (MeOH): λ = 207, 249 nm. H NMR
(500 MHz, CDCl3): δ = 6.37 (dd, J = 15.5, 10.7 Hz, 1 H), 6.03 (d,
J = 10.7 Hz, 1 H), 5.68 (dd, J = 15.5, 6.9 Hz, 1 H), 5.31 (s, 1 H),
5.01 (s, 1 H), 4.44 (m, 1 H), 4.22 (m, 1 H), 2.57 (dd, J = 13.2,
1.9 Hz, 1 H), 2.26 (dd, J = 13.2, 6.9 Hz, 1 H), 1.99 (m, 1 H), 1.97
(m, 2 H), 1.93 (m, 1 H), 1.70 (s, 1 H), 1.61 (m, 2 H), 1.51 (s, 1 H),
1.49 (m, 1 H), 1.43 (m, 5 H), 1.22 (m, 9 H), 1.13 (m, 1 H), 1.05
(m, 1 H), 0.90 (q, J = 12.3 Hz, 1 H), 0.86 (d, J = 6.6 Hz, 3 H), 0.79
(d, J = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 147.6
(C=), 141.4 (=CH), 133.7 (C=), 129.8 (=CH), 124.2 (=CH), 111.9
(=CH2), 71.2 (COH), 71.0 (CHOH), 66.8 (CHOH), 45.1 (CH2),
45.1 (CH), 44.4 (CH2), 42.9 (CH2), 41.8 (CH), 34.8 (CH), 34.8
(CH2), 33.5 (CH2), 30.6 (CH2), 29.3 (2ϫCH3), 28.5 (CH), 26.7
assessed by evaluating [3H]thymidine incorporation. Cells were
seeded in 96-well plates (7500 cells/well) and 1 µCi [methyl-3H]-
thymidine (ICN Biomedicals, Costa Mesa, CA) was added 72 h
after the initiation of treatment. Cells were semi-automatically har-
vested after an additional 6 h of incubation on filter plates only
retaining incorporated thymidine (GF/C Filter and Filtermate Uni-
versal Harvester, Packard Instrument, Meriden, CT). Counting was
performed by using a microplate scintillation counter (Topcount,
Packard).
Biological Evaluation – In Vivo Studies: NMRI mice were obtained
from the Proefdierencentrum of Leuven (Belgium) and fed on a
vitamin D-replete diet (0.2% calcium, 1% phosphate, 2000 U vita-
min Dkg–1; Hope Farms, Woerden, The Netherlands). The hyper-
calcemic effect of the 6D analogues was tested in NMRI mice by
daily subcutaneous injection of 1,25(OH)2D3, its analogues or the
solvent during 7 consecutive days by using serum calcium concen-
tration as parameter.
(CH ), 21.5 (CH ), 17.0 (CH ), 11.9 (CH ) ppm. IR: ν = 3358 (m),
˜
2
2
3
3
2966 (vs), 2922 (vs), 2853 (s), 1724 (vw), 1628 (vw), 1445 (m), 1378
(m), 1225 (m), 1155 (m), 1050 (s), 975 (m), 956 (m), 914 (s), 754
(s) cm–1. MS: m/z (%) = 372 (3), 259 (2), 241 (2), 223 (1), 175 (1),
164 (8), 146 (21), 105 (19), 91 (31), 59 (100), 43 (36).
X-ray Structure Determination: Single-crystal diffraction data were
collected with an Oxford Xcalibur CCD area detector dif-
Acknowledgments
fractometer by using graphite monochromatic Mo-Kα (λ
=
0.71069 Å) radiation. Data reduction and absorption correction
were performed by using CrysAlis RED 1.171.26 (Oxford Diffrac-
tion). The structure was solved by direct methods with the use of
SIR2004[27] and refined by full-matrix least-squares by using
SHELX-97.[28] Hydrogen atoms were generated in calculated posi-
tion by using SHELX-97. CCDC-710052 (for 15) and -710053 (for
14) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
F. V. thanks the I. W. T. for a scholarship. This work was supported
by the Fonds voor Wetenschappelijk Onderzoek (grants G.0508.05
and G.0553.06 for F. W. O.) and by the Centre of Excellence Sym-
BioSys (EF/05/007). Davide Viterbo and Marco Milanesio are
thanked for helpful discussions.
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Received: November 28, 2008
Published Online: February 13, 2009
Eur. J. Org. Chem. 2009, 1720–1737
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