3-Oxa-15-cyclohexyl prostaglandin DP receptor agonists as topical antiglaucoma agents.

Bioorganic & Medicinal Chemistry 10 (2002) 2031–2049

3-Oxa-15-cyclohexyl Prostaglandin DP Receptor Agonists as

Topical Antiglaucoma Agents

Mark R. Hellberg,^aRaymond E. Conrow,^bNajam A. Sharif,^cMarsha A. McLaughlin,^d

John E. Bishop,^a,yJulie Y. Crider,^cW. Dennis Dean,^bKevin A. DeWolf,^b

David R. Pierce,^bVerney L. Sallee,^dRobert D. Selliah,^a,{Bryon S. Severns,^a,b

Steven J. Sproull,^b,#Gary W. Williams,^cPaul W. Zinke^aand Peter G. Klimko^a,*

^aDepartment of Medicinal Chemistry, Alcon Research, Ltd., Pharmaceutical Products Research,

6201 South Freeway, Fort Worth, TX 76134, USA

^bDepartment of Chemical Preparations Research, Alcon Research, Ltd., Pharmaceutical Products Research,

6201 South Freeway, Fort Worth, TX 76134, USA

^cDepartment of Molecular Pharmacology, Alcon Research, Ltd., Pharmaceutical Products Research,

6201 South Freeway, Fort Worth, TX 76134, USA

^dDepartment of In Vivo Pharmacology, Alcon Research, Ltd., Pharmaceutical Products Research,

6201 South Freeway, Fort Worth, TX 76134, USA

Received 25 October 2001; accepted 16 November 2001

Abstract—A series of prostaglandin DP agonists containing a 3-oxa-15-cyclohexyl motif was synthesized and evaluated in several in

vitro and in vivo biological assays. The reference compound ZK118.182 (9b-chloro-15-cyclohexyl-3-oxa-o-pentanor PGF_2a) is a

potent full agonist at the prostaglandin DP receptor. Saturation of the 13,14 oleﬁn aﬀords AL-6556, which is less potent but is still a

full agonist. Replacement of the 9-chlorine with a hydrogen atom or inversion of the carbon 15 stereochemistry also reduces aﬃ-

nity. In in vivo studies ZK118.182 lowers intraocular pressure (IOP) upon topical application in the ocular hypertensive monkey.

Ester, 1-alcohol, and selected amide prodrugs of the carboxylic acid enhance in vivo potency, presumably by increasing bioavail-

ability. The clinical candidate AL–6598, the isopropyl ester prodrug of AL-6556, produces a maximum 53% drop in monkey IOP

with a 1 mg dose (0.003% w/w) using a twice-daily dosing regime. Synthetically, AL–6598 was accessed from known intermediate 1

using a novel key sequence to install the cis allyl ether in the a chain, involving a selective Swern oxidative desilylation of a primary

silyl ether in the presence of a secondary silyl ether. In this manner, 136 g of AL–6598 was synthesized under GMP conditions for

Introduction

process and its causative factors are not completely

Glaucoma, a heterogeneous family of optic neuro-

pathies, is one of the leading causes of blindness in the

developed world. It is characterized by a speciﬁc pattern

of visual ﬁeld loss which is the result of the thinning of

the ganglion cell layer of the retina and the cupping and

excavation of the optic nervehead. Although the disease

understood, elevated intraocular pressure (IOP) is an

important risk factor for loss of visual ﬁeld due to optic

nerve damage.^1,2

Certain prostaglandins such as PGF_2areduce IOP in

man, but also cause conjunctival hyperemia, foreign-

body sensation and ocular pain.³The development of

potent, selective synthetic prostaglandin FP agonists as

clinically eﬀective IOP-lowering agents devoid of many

of these side eﬀects has been an important advance in

the treatment of glaucoma.^3b,c

*Corresponding author. Tel.: +1-817-551-6932; fax: +1-817-551-

4584; e-mail: peter.klimko@alconlabs.com

^yCurrent address: Millenium Pharmaceuticals, 75 Sidney St., Cam-

bridge, MA 02139, USA.

Complementary to these ﬁndings was the discovery that

PGD₂and the selective synthetic DP prostaglandin

agonist BW 245C (Fig. 1) lowered IOP in rabbits with-

out causing the hallmark signs of ocular inﬂammation:

^{Current address: ArQule Inc., 19 Presidential Way, Woburn, MA

01801, USA.

^#Current address: Eli Lilly and Company, Eli Lilly Corporate Center,

Indianapolis, IN 46285, USA.

PII: S0968-0896(02)00016-0

2032

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

Figure 1.

hyperemia, ﬂare and irritation.^4,5Other investigators

conﬁrmed the IOP eﬀect of PGD₂in rabbits but sug-

gested that the natural prostaglandin caused protein

extravasation and eosinophil inﬁltration following topi-

cal ocular application. These investigators also reported

that selective DP prostaglandin agonists such as SQ-

27986, BW 572C85, and BW 192C86 would lower

intraocular pressure in rabbits and were essentially

devoid of the inﬂammatory side eﬀects demonstrated by

PGD₂.^5aÀdClinical trials with PGD₂and BW 245C

conﬁrmed the eﬃcacy of these compounds as ocular

hypotensive agents. However in humans PGD₂and BW

245C produced intense acute conjunctival hyperemia

that was not predicted by the studies in rabbits.^5e

This route to 6 avoided problems of relactonization and

overreduction encountered with g-hydroxy ester inter-

mediates.⁹Oleﬁnation^6a,10of 6 gave enoate 7 (9:1 Z/E).

In contrast, oleﬁnation of the lactol derived from 4 in

this manner was plagued by intramolecular 1,4-addition

of the liberated C-9 alkoxide onto the newly formed

enoate to aﬀord the corresponding tetrahydrofuran. On

multigram scale we used pre-dried (over 4 A molecular

sieves) tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1) as

the K⁺-complexing agent¹¹in place of 18-crown-6¹⁰in

order to avoid problems of cost, toxicity, separation,

and disposal of the crown ether. Chromatographic

separation of the Z and E isomers could be eﬀected at

this stage. We later observed greater ÁR_ffor the Z and

E isomers of diol 8, aﬀording more eﬃcient separation.

We found that the potent, selective DP compound ZK

110.841^5fand the metabolically more stable 3-oxa ana-

logue ZK118.182 ^5f,glowered IOP in Dutch belted (DB)

rabbits. Repeated topical ocular application to the ocu-

lar hypertensive monkey produced a profound (40–

50%) reduction in IOP. These compounds also caused

intense acute conjunctival hyperemia in the guinea pig,

a model that closely reproduces the ocular hyperemic

eﬀect of PGD₂and BW 245C in the human.^5eBased on

these observations, a synthesis program was initiated to

identify the structural features required for the potent

ocular hypotensive activity of ZK118.182 . Below, we

describe the studies leading to the identiﬁcation of the

clinical candidate AL–6598 (Fig. 2) and the develop-

ment of an eﬃcient multigram GMP synthesis of this

interesting compound.

Enoate 7 was elaborated to AL–6598 along lines repor-

ted for the 13,14-dehydro series.⁶Reduction of 7

followed by desilylation gave diol 8. Phase-transfer

alkylation of 8 aﬀorded hydroxy ester 9, which we con-

verted to the ophthalmically preferred isopropyl ester 10

by Ti(OPrⁱ)₄-mediated transesteriﬁcation.¹²Mesylation

of 10 followed by treatment with Bu₄NCl in hot toluene

and removal of the THP groups aﬀorded AL–6598 after

chromatographic separation from the 9-deschloro-

Á^5,6,8,9dienyl side product.^6aUsing these procedures,

136 g of AL-6598 was prepared under GMP conditions

for human clinical evaluation (14 steps, 13% overall

yield).

We also synthesized AL-6598 by way of a modiﬁed Sato

sequence¹³(Scheme 2). Hydrogenation¹⁴of (R)-3-

chloro-1-phenyl-1-propanol (11)¹⁵gave volatile cyclo-

hexyl carbinol 12, which was protected to form the satu-

rated o chain reagent 13. Lithium-chlorine exchange

(THF, 0 ^ꢀC), mixed cuprate formation¹⁶and addition to

chiral enone 14¹³aﬀorded methylene ketone 15. A pro-

tecting group exchange via alcohol 16 gave silyl ether

Results and Discussion

Chemistry

Our synthetic route (Scheme 1) began with the known

lactone 1.⁶Methanolysis of 1 on a 500-g scale aﬀorded

diol 2, which was protected as its bis THP ether 3 and

then hydrogenated to aﬀord 13,14-dihydro compound

4. Alternatively, 2 could be hydrogenated directly in the

basic aqueous extract from the methanolysis, and the

resulting saturated diol then protected to form 4.

Reduction of 4 to the diol followed by Swern oxidation⁷

of the bissilyl derivative 5 provided siloxy aldehyde 6.⁸

Figure 2.

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2033

17. By contrast, the TBDMS or TBDPS ether of 16

suﬀered O!C silyl migration when subjected to these

Li–Cl exchange conditions.¹⁷For a chain installation

we subjected Z-vinylstannane 18^18ato a stereospeciﬁc

The 9-deoxy compound 22 was obtained by mesylation

of alcohol 23, LiEt₃BH per-reduction of the mesylate to

aﬀord 9-deoxy-1-ol 24, PDC/DMF oxidation to the

corresponding 1-acid and esteriﬁcation, deprotection,

and saponiﬁcation (Fig. 3). Attempted production of 22

by radical-mediated reductive dechlorination of 9-chlo-

ride 25 using Bu₃SnH/AIBN caused concomitant Z to E

isomerization of the Á^5,6oleﬁn.²⁰The 5E isomer 26 was

constructed by Wittig reaction of lactol 27 with

19

transmetalation with Me₂Cu(CN)Li₂and added 17 to

the resulting cuprate, aﬀording ketone 19. Reduction¹³

of 19 was followed by removal of the EE group pro-

viding diol 20 which was elaborated as above to give

AL-6598.

Scheme 1. Conditions: (i) K₂CO₃, MeOH, 98%; (ii) DHP, TsOH, CH₂Cl₂, 5^ꢀC, 84%; (iii) 75 psi H₂, 10% Pd/C, EtOAc, 82%; (iv) LiAlH₄, THF,

0 ^ꢀC, 100%; (v) 3 equiv Et₃SiCl, NEt₃, CH₂Cl₂, cat DMAP, 73%; (vi) (COCl)₂, DMSO, CH₂Cl₂, À65 to À50 ^ꢀC, then NEt₃, 5 ^ꢀC, 87%; (vii)

(CF₃CH₂O)₂P(O)CH₂CO₂Me, KHMDS, TDA-1, THF/toluene, À60 to À20 ^ꢀC, 69% pure Z oleﬁn (crude, 8:1 Z:E); (viii) DIBAL-H, THF, À20 to

5 ^ꢀC, 97%; (ix) TBAF, THF, 0 ^ꢀC, 86%; (x) BrCH₂CO₂Bu^t, KOH, Bu₄NHSO₄, toluene/water, 86%; (xi) Ti(OPr-i)₄, i-PrOH, heat, 96%; (xii) (a)

MsCl, pyridine, 0 ^ꢀC; (b) Bu₄NCl, toluene, 55 ^ꢀC; (c) AcOH/water, 65 ^ꢀC, 54% from 10 after HPLC puriﬁcation.

Scheme 2. Conditions: (i) H₂, 5% Rh/Al₂O₃, MeOH, 55%; (ii) ethyl vinyl ether, PPTS, CH₂Cl₂, 97%; (iii) (a) Li, 4,4⁰-di-t-butylbiphenyl, THF, 0 ^ꢀC;

(b) À45 ^ꢀC, 13/THF; (c) lithium (2-thienyl)cyanocuprate/THF; (d) 14/THF; 57% yield of 15 after quenching; (iv) PPTS, isopropanol, 77%; (v)

TBSOTf, i-Pr₂NEt, CH₂Cl₂/DMF, 80%; (vi) MeLi, CuCN, THF, 0 ^ꢀC, then add 18, rt, then cool to À78 ^ꢀC, then add 17/THF, 10 min, aq NH₄Cl

quench, 72%; (vii) l-Selectride, THF, À78 ^ꢀC, 56%; (viii) PPTS, isopropanol/ether, 76%; (ix) BrCH₂CO₂Bu^t, NaOH, Bu₄NHSO₄, toluene/water,

78%; (x) Ti(OPr-i)₄, isopropanol, heat, 75%; (xi) MsCl, pyr, 0 ^ꢀC; (xii) Bu₄NCl, toluene, heat; (xiii) HF, THF, 0 ^ꢀC to rt, 63% yield from 21 of 6598/

diene as a 3.5:1 mixture.

2034

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

Ph₃P¼CHCO₂Me in the presence of acetic acid to

aﬀord the E enoate 28 (99%), the acidic conditions

suppressing intramolecular 1,4-addition.²¹Compounds

with the 15b alcohol relative stereochemistry, such as

29, were synthesized from the 15-epimer⁶30 of lactone

1. The 15-methoxy acid 32 was prepared from the

t-butyl ester 32 by selective t-butyldimethylsilylation of

the C-11 hydroxyl, methylation of the C-15 hydroxyl,

desilylation, and saponiﬁcation. The primary amide 33

was prepared by NH₃/NH₄Cl treatment of 32. The sec-

ondary and tertiary amides 34 and 35 were formed by

Weinreb amination of AL–6598 and 32, respectively.

has low aﬃnity for the DP receptor, and is a weak par-

tial agonist.

Saturation of the 13,14 oleﬁn of ZK118.182 to aﬀord

AL-6556 causes a greater than 60-fold decrease in aﬃ-

nity and an almost 90-fold reduction in functional

potency while maintaining full eﬃcacy Within the series

of 13,14-dihydro derivatives, the 15b-hydroxy (38), 5,6-

dihydro (39), and the 9b-H (40) compounds have simi-

lar aﬃnity for the DP receptor, being slightly less potent

than AL-6556. In the functional assay, 39 and 38 are

similar in potency to AL-6556 and are partial and full

agonists, respectively. Inversion of the carbon 15 rela-

tive stereochemistry from a to b in the 13,14-dihydro

series surprisingly only slightly attenuates receptor aﬃ-

nity and functional potency, as compared to the marked

decrease observed with this structural change in the

13,14-alkene series. The 9b-H compound 40 is a full

agonist but has 2-fold lower aﬃnity for the DP receptor

and is 5-fold less potent than AL-6556 in the functional

assay.

Pharmacology

The compounds in Table 1 were evaluated for their

aﬃnity and eﬃcacy at the DP prostaglandin receptor

and for IOP lowering eﬀect in the Dutch belted rabbit

and the ocular hypertensive monkey. The carboxylic

acid was used in all in vitro studies since it is believed to

be the pharmacologically active form of the compound.

The isopropyl or t-butyl ester derivatives are prodrugs

that facilitate corneal penetration and delivery of the

carboxylic acid to aqueous humor. The esters were used

in the in vivo experiments unless otherwise noted.

The 15a-methyl ether 31 has low aﬃnity for the DP

receptor and is inactive in the functional assay, suggest-

ing that the increased bulk of the methyl group is not

tolerated and/or that the receptor requires a hydrogen

bond donor for agonist activity. The amides 33, 35, and

41 and the 1-hydroxy derivative 42 were prepared as

prodrugs. As expected, these compounds have low aﬃ-

nity for the DP receptor and are inactive at concentra-

tions up to 100 mM in the functional assay.

In vitro studies. The K_iand EC₅₀values for ligand

binding to and functional activity at the DP receptor for

relevant compounds are shown in Table 2. The parent

compound ZK118.182 is a high aﬃnity potent full ago-

nist at the DP prostaglandin receptor. The 5E (26) and

15b-hydroxy (36) isomers are over 400-fold less potent,

the former being a full, and the latter a partial, agonist.

The 9b-H compound 22 is also a full agonist, being

about 25 and 90 times less potent than ZK118.182 in

binding and functional assays, respectively. The 1-alco-

hol derivative 37, prepared as a carboxylic acid prodrug,

In vivo studies. Compounds were evaluated for their

eﬀect on IOP in rabbits. Compounds having a favorable

proﬁle were advanced into the ocular hypertensive

monkey. The rabbit and monkey IOP data are reported

in Tables 3 and 4, respectively.

Figure 3.

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2035

The carboxylic acid ZK118.182 causes a transient

reduction in IOP in the rabbit following a 1-mg dose but

produces a sustained reduction in IOP following a 20-mg

dose. The compound also lowers IOP in the ocular

hypertensive monkey following a 5-mg application. As

expected the isopropyl (25) and t-butyl (43) ester pro-

drugs of ZK118.182 are much more potent than the

acid in the rabbit and monkey, supporting the hypoth-

esis that acid esteriﬁcation facilitates corneal penetra-

tion and increases bioavailability. Following a 10-mg

dose, the 5E ester 44 unexpectedly causes a large initial

increase in IOP prior to exerting the expected ocular

Table 1. 3-Oxa-15-cyclohexyl prostaglandin analogues

Compd

A

5,6

X

13,14

Y

ZK118.182

CO₂H

CO₂Prⁱ

CO₂H

CO₂Prⁱ

CO₂H

CO₂Prⁱ

CO₂H

CO₂Bu^t

CONH₂

CONHBuⁿ

CONMe₂

CO₂H

CH₂OH

CO₂H

Z-CH¼CH

E-CH¼CH

Z-CH¼CH

CH₂CH₂

Z-CH¼CH

E-CH¼CH

Z-CH¼CH

CH₂CH₂

Cl

H

E-CH¼CH

CH₂CH₂

E-CH¼CH

CH₂CH₂

E-CH¼CH

CH₂CH₂

a-OH

b-OH

a-OMe

a-OH

b-OH

a-OH

b-OH

a-OH

b-OH

a-OH

a-OMe

AL–6598

AL–6556

22

25

26

29

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

Cl

H

Cl

H

Cl

H

Cl

CO₂H

CONHMe

CH₂OH

CO₂Bu^t

CO₂Prⁱ

CO₂Bu^t

CH₂CH₂

E-CH¼CH

CH₂CH₂

Z-CH¼CH

Table 2. In vitro activities of 3-oxa-15-cyclohexyl prostaglandin DP receptor agonists

DP aﬃnity

DP activity

Compd

A

5,6

X

13,14

Y

K_iꢁSEM^a

(mM)

EC₅₀ꢁSEM^a

Maximum

response (%)

(mM)

ZK118.182

CO₂H

Z-CH¼CH

E-CH¼CH

Z-CH¼CH

CH₂CH₂

Cl

H

E-CH¼CH

CH₂CH₂

E-CH¼CH

CH₂CH₂

E-CH¼CH

CH₂CH₂

a-OH

a-OMe

a-OH

b-OH

a-OH

b-OH

a-OH

0.050ꢁ0.0088

3.2ꢁ0.46

1.2ꢁ0.45

35ꢁ2.5

25ꢁ17

0.014ꢁ0.0041

0.80ꢁ0.18

0.89ꢁ.23

0.94ꢁ0.22

>100,000

n.d.^b

98

92.5

87

AL-6556

22

26

31

33

34

35

36

37

38

39

40

41

Cl

H

93

n.d.^b

51

CONH₂

CONH-n-Bu

CONMe₂

CO₂H

CH₂OH

CO₂H

CONHMe

CH₂OH

140ꢁ60

n.d.^b

110ꢁ13

22ꢁ7.9

66ꢁ15

>100,000

5.3ꢁ1.2

14.8ꢁ4.5

1.22ꢁ0.45

1.3ꢁ0.36

4.6ꢁ1.1

43

83.6

52

5.9ꢁ1.2

7.2ꢁ0.79

6.8ꢁ0.92

110ꢁ12

47ꢁ36

Z-CH¼CH

79

Cl

>100,000

n.d.^b

42

^aSEM, standard error of the mean.

^bn.d., not determined.

2036

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

hypotensive eﬀect. The 9b-H analogue 45 at 0.1 and

0.3 mg topical ocular doses lowers IOP in the rabbit

eﬃcaciously but with a shorter duration of action

than the corresponding 9b-chloride. The 15b-hydroxy

compound 46 does not lower IOP in the rabbit at doses

100-fold higher than the ocular hypotensive dose of the

15a-hydroxy isomer 25. The ineﬀectiveness, of 46 is

consistent with the in vitro data for the corresponding

acid. Interestingly, the 1-alcohol prodrug 37 does not

lower IOP in the rabbit at doses well above those that

Table 3. Rabbit IOP data

Compd

Dose (mg)

Baseline IOP

(mm Hg)

% ReductionꢁSEM^a

1 h

2 h

3 h

5 h

ZK118.182

20

1.0

3

32.9

32.2

23.3

29.6

24.6

25.3

26.4

26.7

24.9

25.1

28.1

24.4

26.6

24.8

26.6

26.5

28.2

27.5

28.1

27.8

32.5

24.6

21.8

22.3

22.8

21.6

27.0

25.9

27.5

27.7

26.6

26.0

16.8ꢁ5.2

18.7ꢁ2.6

3.0ꢁ5.9

22.6ꢁ4.6

4.9ꢁ5.2

9.9ꢁ2.6

15.6ꢁ2.1

20.0ꢁ2.1

13.0ꢁ1.8

14.7ꢁ3.4

8.8ꢁ3.5

14.5ꢁ4.7

14.3ꢁ3.5

7.5ꢁ2.6

4.3ꢁ3.6

14.2ꢁ4.4

4.3ꢁ4.0

8.0ꢁ3.0

9.7ꢁ3.0

16.3ꢁ2.2

14.4ꢁ4.2

(+)^b0.2ꢁ2.0

28.2ꢁ3.6

9.7ꢁ3.7

8.8ꢁ4.7

20.6ꢁ1.6

15.2ꢁ6.3

9.6ꢁ4.3

9.8ꢁ4.3

0.2ꢁ2.7

8.9ꢁ2.4

4.3ꢁ2.9

n.d.^c

25.2ꢁ1.3

5.4ꢁ4.6

23.8ꢁ3.0

(+)^b6.9ꢁ2.0

22.6ꢁ1.9

8.2ꢁ2.2

AL–6598

20.3ꢁ3.1

11.5ꢁ2.2

14.3ꢁ2.6

7.9ꢁ1.2

1

13.9ꢁ2.4

24.1ꢁ0.26

16.9ꢁ13.1

16.5ꢁ4.4

16.3ꢁ2.4

4.9ꢁ8.1

25

29

33

34

35

37

41

0.03

0.01

10

1

30

10

30

3

100

3

1

10

3

10

0.1

0.03

10

1

0.3

0.1

3

1

3

1

10

1

7.9ꢁ1.9

5.1ꢁ1.4

11.2ꢁ3.3

5.0ꢁ1.4

12.9ꢁ5.0

3.7ꢁ2.9

21.6ꢁ4.0

17.1ꢁ2.6

13.1ꢁ2.5

(+)^b1.8ꢁ4.4

16.4ꢁ3.5

12.8ꢁ4.9

8.5ꢁ2.7

25.9ꢁ3.2

24.2ꢁ1.1

25.1ꢁ4.2

6.0ꢁ4.2

18.4ꢁ2.8

5.1ꢁ3.8

(+)^b0.9ꢁ2.2

12.5ꢁ3.1

10.2ꢁ3.4

6.4ꢁ3.5

26.5ꢁ1.5

11.3ꢁ5.2

7.5ꢁ3.8

4.8ꢁ0.85

10.3ꢁ3.3

13.4ꢁ3.1

0.9ꢁ2.3

13.5ꢁ2.7

21.1ꢁ2.7

12.6ꢁ2.1

(+)^b5.1ꢁ2.8

28.4ꢁ3.1

8.9ꢁ1.7

8.1ꢁ1.8

29.0ꢁ4.1

11.6ꢁ2.3

(+)^b7.3ꢁ3.7

22.5ꢁ3.7

9.3ꢁ3.0

42

43

33.1ꢁ3.5

10ꢁ3.7

44

45

46

47

48

49

(+)^b30.1ꢁ8.3

17.6ꢁ1.8

32.7ꢁ5.6

21.4ꢁ3.6

11.3ꢁ3.7

1.5ꢁ3.8

16.4ꢁ4.8

14.3ꢁ2.2

10.2ꢁ6.0

6.2ꢁ3.3

19.2ꢁ3.7

6.8ꢁ2.3

3.5ꢁ5.9

0.1ꢁ1.7

5.3ꢁ5.8

1.4ꢁ3.9

10.7ꢁ6.4

7.6ꢁ2.5

0.7ꢁ3.9

20.0ꢁ2

1.8ꢁ2.5

9.9ꢁ3.5

2.1ꢁ4.1

2.7ꢁ5.1

5.9ꢁ7.3

6.9ꢁ3.6

0.9ꢁ3.6

2.5ꢁ3.4

n.d.^c

(+)^b6.7ꢁ3.9

(+)^b9.7ꢁ4.4

10

3

0.6ꢁ41

3.3ꢁ2.6

2.8ꢁ3.4

2.7ꢁ3.6

5.5ꢁ2.2

4.0ꢁ3.2

3.4ꢁ3.4

0.8ꢁ3.2

^aSEM, standard error of the mean.

^b(+)=increase in IOP above baseline.

^cn.d., not determined.

Table 4. Monkey IOP data

Compd

Dose (mg)

Baseline IOP

(mm Hg)

Time after dose/dose number

2 h/5 4 h/5

16 h/4

6 h/5

% Reduction in IOPꢁSEM^a

ZK118.182

AL–6598

5

1

30.3

38.7

36.7

35.3

38.7

32.3

35.3

38.6

37.0

37.6

32.3

33.3

37.8

31.3

31.4

12.6ꢁ3.6

41ꢁ3.1

25.5ꢁ4.5

52.5ꢁ5.4

35.8ꢁ5.3

46.3ꢁ3.8

52.1ꢁ2.4

41.4ꢁ5.33

25.0ꢁ6.6

42.2ꢁ5.8

10.9ꢁ3.9

24.3ꢁ3.6

17.9ꢁ5.1

44.3ꢁ3.1

42.2ꢁ4.9

52.8ꢁ3.3

24.4ꢁ4.6

30.6ꢁ3.4

48.1ꢁ5.2

34.6ꢁ5.1

31.7ꢁ6.9

50.7ꢁ2.9

33.6ꢁ6.2

31.1ꢁ5.2

48.3ꢁ5.7

15.7ꢁ4.3

18.4ꢁ4.6

14.0ꢁ4.4

35.8ꢁ3.3

33.7ꢁ5.2

54.7ꢁ3.4

25.8ꢁ3.6

26.2ꢁ4.6

35.7ꢁ5.5

31.3ꢁ6.0

31.6ꢁ4.6

45.7ꢁ3.4

29.8ꢁ7.3

22.2ꢁ7.4

35.9ꢁ7.8

13.8ꢁ3.8

13.7ꢁ4.0

14.1ꢁ4.8

30.3ꢁ2.5

28.5ꢁ4.4

53.1ꢁ4.1

21.1ꢁ4.1

0.3

0.03

10

3

1

3

17.8ꢁ4.5

34.7ꢁ3.6

48.7ꢁ4.9

30ꢁ6.1

25

29

20.6ꢁ6.4

25.5ꢁ7.6

1.3ꢁ2.6

21.6ꢁ3.4

3ꢁ3.4

33

1

3

34

35

37

42

43

30

0.3

3

1

0.1

35.2ꢁ2.7

28.0ꢁ3.9

47.6ꢁ2.6

19.2ꢁ2.9

^aSEM, standard error of the mean.

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2037

are eﬃcacious for the esters. Unlike the observed lack of

activity in the rabbit, 37 eﬀectively lowers IOP in the

monkey at a 0.3 mg dose. This observation suggests that

the rabbit, unlike the monkey, does not metabolize

1-alcohol prostaglandin derivatives to the carboxylic

acid when the compound is administered topically to

the eye. The esters of the 13,14-dihydro derivative of ZK

118.182 (AL–6598 and 32) are 10- to 100-fold less

potent but are just as eﬃcacious in reducing IOP in the

rabbit and the monkey as the parent esters 25 and 43.

The 15b-hydroxy compound in the 13,14 dihydro series

(29) produces a modest eﬀect on IOP in rabbits and is

active only at the early time points. In the ocular

hypertensive monkey 29 is less potent than the 15a

isomer AL–6598 but is equally eﬃcacious.

mM potency. Conversion of the carboxylic acid to an

amide or reduction to the 1-alcohol completely abol-

ishes in vitro eﬃcacy. Interestingly inversion of carbon

15 hydroxyl stereochemistry from a to b greatly reduces

functional potency and eﬃcacy when the 13,14 alkene is

present but only slightly aﬀects these values when this

position is saturated.

As reported with the prostaglandin FP derivatives, ester

prodrugs enhance the potency of the compounds pre-

sumably by facilitating the corneal absorption of the

compounds. These studies have shown that the 1-alco-

hol derivatives are also eﬀective prodrugs for these

analogues in the monkey, but not in the rabbit. The

primary amide is potent and eﬃcacious in the rabbit

and monkey, while secondary and tertiary amides show

reduced activity. The lack of potency and in some cases

limited eﬃcacy observed with these amide derivatives

may be due to poor corneal penetration and/or slow

rate of hydrolysis. The delayed onset of action of some

of the amide derivatives suggests that the slow rate of

hydrolysis may be reducing the bioavailability of the

active carboxylic acid.

As was seen with the 13,14-alkene analogue, application

of the 9b-H derivative 47 to the rabbit eye results in a

rapid onset of action that is brief in duration compared

to corresponding 9b-Cl compound AL–6598. Both the

5,6,13,14-tetrahydro (48) and the 15-methoxy-13,14-

dihydro (49) compounds are inactive at doses of 10 mg

in the rabbit. As seen with the alkene series the 1-

alcohol derivative 42 does not lower IOP at doses 3- to

10-fold higher than the eﬀective dose of AL–6598 in

the rabbit. However, 42 is eﬀective in lowering IOP in

the monkey following a 3-mg dose.

Based on the profound eﬃcacy of these compounds as

ocular hypotensive agents and additional preclinical

studies demonstrating a positive eﬀect on ocular blood

ﬂow one of these compounds, AL–6598, was selected for

human clinical evaluation. The results of these studies

will be reported in due course.

The activity of the amide derivatives in the 13,14-dihy-

dro series depends on the degree of substitution on

nitrogen. The primary amide 33 and the secondary

methyl amide 41 are 3- to 10-fold less potent than AL–

6598 in the rabbit IOP model. In the monkey the pri-

mary amide produces a profound reduction in IOP at a

3-mg dose. In the rabbit the n-butyl amide of AL-6556

(34) appears to have a delayed onset of action with the

maximum reduction in IOP at the 5-h observation

point. The compound produces a modest reduction in

IOP at 3 mg in the monkey, the only dose tested. In the

rabbit the dimethyl amide 35 is active at doses that are

30- to 100-fold higher than that of the ester. It modestly

reduces IOP in the monkey at 30 mg, the only dose tes-

ted. Since the amides are inactive in the in vitro func-

tional assay, these observations suggest that the amides

evaluated are being hydrolyzed to the pharmacologi-

cally active acid when applied topically to the eye, with

increasing nitrogen substitution leading to slower clea-

vage. Irrespective of the nitrogen substitution pattern

the amides are not cleaved as readily as the isopropyl or

t-butyl esters.

Experimental

Chemistry general methods

Abbreviations used include: DMAP, 4-(dimethylami-

no)pyridine; DIBAL-H, diisobutylaluminum hydride;

TBAF, tetra-n-butylammonium ﬂuoride. Unless other-

wise noted, all ¹H NMR spectra were acquired in

CDCl₃solvent on a Varian Gemini 200 spectrometer

operating at a ﬁeld strength of 200 MHz, and all ¹³C

NMR and DEPT spectra were acquired in CDCl₃on

the same instrument operating at a ﬁeld strength of

50.4 MHz. The compound ZK118.182 and its t-butyl

ester 43 were kindly provided by Schering AG, Berlin,

Germany. For reactions without added water, solvents

used were anhydrous grade from Aldrich Chemical

Company and were used without further puriﬁcation.

Unless otherwise stated, all reactions without added

water were run under a positive pressure of nitrogen,

and all temperatures quoted refer to external temperatures.

‘Dry THF’ refers to THF which was freshly distilled from

potassium benzophenone ketyl. Concentration refers to

removal of solvent in vacuo on a rotary evaporator.

Reactions were monitored by TLC on E. Merck Silica

Gel 60 F₂₅₄plates, with visualization by UV light or

staining with either ethanolic phosphomolybdic acid or

2% aq KMnO₄. Column chromatographic puriﬁcations

were performed under positive air ﬂow using 230–400

mesh silica gel from E.M. Science. Chromatography

solvents used were HPLC grade from E.M. Science.

Low resolution mass spectra (LRMS) were acquired on

Conclusions

A series of 3-oxa-15-cyclohexyl prostaglandins has been

synthesized for evaluation in in vitro prostaglandin DP

binding and functional assays and in in vivo rabbit and

monkey IOP assays. All structural modiﬁcations to the

parent compound ZK118.182 reduce receptor aﬃnity

and functional potency by 2–3 orders of magnitude, but

many of these analogues maintain full agonist eﬃcacy.

Replacement of the 9-chlorine atom with a hydrogen or

saturation of the 13,14 oleﬁn aﬀords full agonists with

2038

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

a Finnegan TSQ 46 triple quadrupole mass spectro-

meter when operated in the fast-atom bombardment

(FAB) or chemical ionization (CI; isobutane as ionizing

gas) modes and on a Voyager RP laser desorption time-

of-ﬂight mass spectrometer when using the matrix-

assisted laser desorption ionization (MALDI) method.

High resolution mass spectra (HRMS) were acquired in

the CI mode using isobutane as the ionization gas at the

University of Texas Mass Spectrometry Facility, Aus-

tin, TX, USA.

tions was 1179 g (84% yield). MALDI LRMS, m/z 471

for (M+Na)⁺.

[3aR,4R(3R),5R,6aS] - 4 - [3 - Cyclohexyl - 3 - (tetrahydro-

pyran-2-yloxy)propyl]-5-(tetrahydropyran-2-yloxy)hy-

droxyhexahydro-2H-cyclopenta[b]furan-2-one (4).

A

solution of 3 (658 g, 1.47 mol), in ethyl acetate (8.8 L)

was transferred to a 20 L Buchi hydrogenation appara-

tus using vacuum. The catalyst (10% w/w Pd/C, 7.8 g)

was added through the charging port via a small powder

funnel. The system was sealed, purged three times with

N₂, and stirred under 5 bar of H₂for 20 h. After purging

the system with N₂the contents were removed and ﬁl-

tered through Celite. The reactor was washed with ethyl

acetate (2ꢂ4 L) and ﬁltered through Celite. The com-

bined ﬁltrates were concentrated to provide a white

solid, which was triturated with hexane, ﬁltered, and air

dried to aﬀord 446 g (67%) of 4. The ﬁltrate was con-

centrated and the residue was slurried with water, ﬁl-

tered, washed with hexane, and air dried to aﬀord

additional 4 containing a small amount of the isomeric

15-ketone (214 g total). This impure fraction was com-

bined with a 335 g similar fraction from a hydrogen-

ation run that started with 541 g (1.21 mol) of 3 (total

starting material=1199 g from the two runs), and the

combined fractions were puriﬁed by chromatography

on 7 kg of silica gel eluting with 1:1 hexane:ethyl ace-

tate. The total amount of 4 isolated from both runs was

996 g (82% yield). MALDI LRMS, m/z for (M+Na)⁺

at 473.

[3aR,4R(1E,3S),5R,6aS]-4-(3-Cyclohexyl-3-hydroxy-1-

propenyl)-5-hydroxyhexahydro-2H-cyclopenta[b]furan-2-

one (2). A mixture of [3aR,4R(1E,3S),5R,6aS]-4-[3-

cyclohexyl-3-hydroxy-1-propenyl]-5-(benzoyloxy)hexahydro

- 2H-cyclopenta[b]furan-2-one (1) (500 g, 1.3 mol) and

K₂CO₃(180 g, 1.3 mol) in methanol (5 L) was stirred for

2 h. The pH of the mixture was adjusted to ca. 2 by the

addition of 1 M aq HCl (2 L) and concentrated until the

product separated as an oil. The aqueous phase was

saturated with NaCl and was extracted with four por-

tions of ethyl acetate. The combined organic extracts

were washed with saturated NaCl, dried over sodum

sulfate, and concentrated. The oily amber residue was

triturated with 25% ether in hexane (1.5 L). Filtration

and air drying of the white solid product aﬀorded 2

(358 g, 98%). ¹³C NMR d 177.00 (C), 135.29 (CH),

131.11 (CH), 82.47 (CH), 77.37 (CH), 75.30 (CH), 55.25

(CH), 43.38 (CH), 42.44 (CH), 39.62 (CH₂), 34.04

(CH₂), 28.79 (CH₂), 26.42 (CH₂), 26.02 (CH₂), 25.94

(CH₂). MALDI LRMS, m/z for (M+Na)⁺at 303.

(9S,11R,15R)-11,15-Bis(tetrahydropyran-2-yloxy)-15-

cyclohexyl-2,3,4,5,6,16,17,18,19,20-decanor - 9 - (triethyl-

siloxy)prostanol triethyl silyl ether (5). A 12 L three

neck round bottom ﬂask was charged with THF (3 L)

and was cooled to 0 ^ꢀC. LiAlH₄(47 g, 1.24 mol) was

added and the suspension was cooled to an internal

temperature of 0 ^ꢀC using a dry ice/i-PrOH bath. A

solution of lactone 4 (561 g, 1.24 mol) in THF (2 L) was

added to the stirred suspension over 60 min, maintain-

ing the internal temperature between 0 and À3 ^ꢀC. After

stirring for 60 min the suspension was quenched by the

sequential, slow addition of water (50 mL), 15% aq

NaOH (150 mL), and water (50 mL). After stirring for

an additional 30 min the mixture was ﬁltered through

Celite and the ﬁlter cake was washed with ethyl acetate

(6 L). Saturated NaCl (1 L) was added to the ﬁltrate and

the layers were separated. The combined organic layers

were dried over Na₂SO₄, ﬁltered, and concentrated to

aﬀord 559 g (100%) of the diol (9S,11R,15R)-11,15-

bis(tetrahydropyran-2-yloxy)-15-cyclohexyl-2,3,4,5,6,

16,17,18,19,20-decanor-9-hydroxyprostanol, which was

used in the next step without any further puriﬁcation.

[3aR,4R(1E,3S),5R,6aS]-4-[3-Cyclohexyl-3-(tetrahydro-

pyran-2-yloxy)-1-propenyl]-5-(tetrahydropyran-2-yloxy)-

hydroxyhexahydro-2H-cyclopenta[b]furan-2-one (3). A

12-L three-neck round bottom ﬂask was charged with

diol 2 (524 g, 1.87 mol) and CH₂Cl₂(5 L). The solu-

tion was cooled to 5 ^ꢀC and 3,4-dihydro-2H-pyran

(430 mL, 4.67 mol) was added in one portion. The

catalyst p-toluenesulfonic acid monohydrate (2.5 g,

13 mmol) was added and the solution was stirred at 0 ^ꢀC

for 30 min. The reaction was quenched by the addition

of saturated NaHCO₃(1.5 L) and was stirred at room

temperature for 2.5 h. The phases were separated, the

aqueous phase was extracted with CH₂Cl₂(1 L) and the

combined organic layers were washed with saturated

NaCl (500 mL) and dried over Na₂SO₄. The solvent was

concentrated and 25% ether in hexane (4 L) was added

to the oily residue. The mixture was concentrated until

precipitation of a solid was evident. The solution was

allowed to stand for 72 h. The white solid product was

collected by ﬁltration, washed with hexane, and air

dried to provide of bis-THP ether 3 (513 g). The ﬁltrate

was concentrated and the oily residue was triturated

with 25% ether in hexane to provide an additional lot of

3 (96 g). Repetition of this process aﬀorded a third crop

of 3 (37 g; total amount=660 g=79% yield). The

remaining ﬁltrate was concentrated and puriﬁed by

chromatography with the corresponding ﬁltrate from a

358 g run of this reaction. (total starting material for the

two runs=882 g=3.14 mol). The chromatography was

performed using 7 kg of silica gel eluting with 20% ethyl

acetate in hexane. The total isolated from the two reac-

A 22 L three-neck round-bottom ﬂask was charged with

a solution of the diol reduction product from above

(558 g, 1.23 mol) in CH₂Cl₂(6 L). The reagents DMAP

(1.5 g, 0.012 mol), NEt₃(1012 mL, 7.37 mol), and

Et₃SiCl (610 mL, 3.69 mmol) were added sequentially,

resulting in the formation of a white precipitate. The

suspension was stirred for 2.5 h and was quenched by

the addition of water (2.5 L). The phases were separated

and the aqueous layer was extracted with CH₂Cl₂(1 L).

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2039

The combined organic layers were washed with satu-

rated NaCl (4 L), dried over Na₂SO₄and ﬁltered, and

the ﬁltrate was concentrated to aﬀord ca. 1016 g of a

crude oil. Residual Et₃SiOH was distilled away using a

Kugelrohr apparatus and the residue was puriﬁed by

chromatography on a Kilo-Prep 250 liquid chromato-

graph eluting with 5% ethyl acetate in hexane to aﬀord

maintaining the internal temperature below À50 ^ꢀC.

After stirring at À50 ^ꢀC for 1 h the mixture was warmed

to À20 ^ꢀC and maintained at that temperature for 15 h.

Saturated NH₄Cl (2 L) was added and the mixture was

warmed to room temperature. The suspension was ﬁl-

tered and the ﬁlter cake was washed with ethyl acetate

(2 L). The phases of the ﬁltrate were separated and the

aqueous phase was extracted with ethyl acetate (2ꢂ1 L).

Aqueous citric acid (10% w/v, 2 L) was added to the

combined organic layers and the mixture was vigorously

stirred for 10 min. The phases were separated and the

organic phase was washed with saturated NaHCO₃

(2ꢂ2 L) and saturated NaCl (2 L), dried over Na₂SO₄,

ﬁltered, and concentrated to aﬀord 430 g of crude pro-

duct. Proton NMR analysis of the crude indicated an

8:1 ratio of Z:E isomers. The residue was ﬁrst puriﬁed

by passing through a 15% ethyl acetate in hexane solu-

tion of the residue through a sintered glass funnel con-

taining 4 kg of silica gel to provide 311 g of a crude oil.

This oil was further puriﬁed by chromatography on a

KiloPrep 250 using a 10 cm tallꢂ60 cm diameter silica

gel cartridge of 32–63 m KP-Sil silica gel eluting with 5%

ethyl acetate in hexane to aﬀord of cis-crotonate 7

(228 g, 69%) without any detectable trans diastereomer

by proton NMR analysis. ¹H NMR d 6.35 (m, 1H), 5.78

(broad d, J=12 Hz, 1H), 4.65 (m, 2H), 4.28 (m, 1H),

3.90 (m, 2H), 3.70 (s, 3H), 3.55–3.30 (m, 3H), 2.80 (m,

2H), 2.35–2.05 (m, 1H), 2.00–1.10 (broad m, 30H), 0.95

(broad t, 9H), 0.60 (broad q, 6H). MALDI LRMS, m/z

for (M+Na)⁺at 645.

1

bissilyl ether 5 (613 g, 73%). H NMR (characteristic

peaks only) d 4.62 (m, 2H), 4.15–3.25 (br m, 7H), 2.30–

1.15 (br m, 18H), 0.95 (br t, 18H), 0.65 (br q, 12H).

MALDI LRMS, m/z for (M+Na)⁺at 705.

(9S,11R,15R)-11,15-Bis(tetrahydropyran-2-yloxy)-15-

cyclohexyl-2,3,4,5,6,16,17,18,19,20-decanor - 9 - (triethyl-

siloxy)prostanal (6). A 12-L three-neck round bottom

ﬂask was charged with (COCl)₂(156 mL, 1.8 mol) and

CH₂Cl₂(1.6 L). The solution was cooled to an internal

temperature of À55 ^ꢀC and a solution of DMSO

(323 mL, 4.5 mol) in CH₂Cl₂(700 mL) was added over

1 h while maintaining the internal temperature below

À50 ^ꢀC. The mixture was stirred at an internal tem-

perature of À60 ^ꢀC for 1 additional hour and a solution

of bissilyl ether 5 (613 g, 900 mmol) in CH₂Cl₂(1.5 L)

was added over another 1.5 h while maintaining the

internal temperature below À55 ^ꢀC. After an additional

3.5 h NEt₃(752 mL, 5.4 mol) was added over 30 min as

the internal temperature rose to À50 ^ꢀC. After stirring at

an internal temperature of À65 ^ꢀC for 1.5 h the suspen-

sion was placed in a 5 ^ꢀC refrigerator for 15 h. Water

(3 L) was added to the reaction, the mixture was

warmed to room temperature and was stirred for

30 min, and the phases were separated. The organic

phase was washed with water (2ꢂ3 L) and saturated

NaCl (2ꢂ2 L). The combined aqueous layers were

extracted with CH₂Cl₂(2ꢂ2 L) and the combined

organic phases were washed with saturated NaCl (1 L),

dried over Na₂SO₄, ﬁltered, and concentrated. The resi-

due was dissolved in 1:1 v/v ether/hexane (2 L) and

washed with water (2ꢂ1 L) and saturated NaCl (1 L).

The organic phase was dried over Na₂SO₄, ﬁltered, and

concentrated. The residue was puriﬁed by chromato-

graphy in two portions on 7 kg of silica gel eluting with

a 10% ethyl acetate!20% ethyl acetate in hexane gra-

dient to aﬀord aldehyde 6 (442 g, 87%). ¹H NMR d 9.80

(br s, 1H), 4.62 (m, 2H), 4.20 (m, 1H), 3.85–3.60 (m,

3H), 3.40 (m, 3H), 2.80 (m, 1H), 2.45–2.05 (m, 4H),

1.95–1.10 (br m, 27H), 0.95 (br t, 9H), 0.55 (br q, 6H).

(5Z)-(9S,11R,15R)-11,15-Bis(tetrahydropyran-2-yloxy)-

15-cyclohexyl-9-hydroxy-2,3,4,16,17,18,19,20-octanor-5-

prostenol (8). A 12-L four-neck round-bottom ﬂask was

charged with a solution of ester 7 (273 g, 440 mmol) in

THF (2.7 L). The solution was cooled to an internal

temperature of À20 ^ꢀC and a 1.5 M solution of diisobu-

tylaluminum hydride in toluene (880 mL, 1.32 mol) was

added over 30 min while maintaining the internal tem-

perature below 5 ^ꢀC. The reaction was stirred for 2 h

and was quenched by the addition of methanol

(250 mL) and saturated Na K tartrate tetrahydrate

(2 L). The mixture was warmed to room temperature

and was extracted with ethyl acetate (2ꢂ2 L). The com-

bined organic layers were washed with water (2 L) and

saturated NaCl (2ꢂ2L). The organic phase dried over

Na₂SO₄, ﬁltered, and concentrated, and the residue was

dried under vacuum for 15 h using a Kugelrohr apparatus

to aﬀord alcohol (5Z)-(9S,11R,15R)-11,15-bis(tetrahy-

dropyran-2-yloxy)-15-cyclohexyl-2,3,4,16,17,18,19,20-

octanor-9-(triethylsiloxy)-5-prostenol (250 g, 97%), which

was used in the next step without further puriﬁcation.

¹H NMR d 5.65 (m, 2H), 4.65 (m, 2H), 4.30–3.25 (br m,

5H), 2.40–2.05 (br m, 4H), 2.00–1.10 (br m, 32H), 1.00

(br t, 9H), 0.60 (br q, 6H). MS, m/z at 617 for

(M+Na)⁺.

(5Z)-(9S,11R,15R)-11,15-Bis(tetrahydropyran-2-yloxy)-

15-cyclohexyl-2,3,4,16,17,18,19,20-octanor-9-(triethyl-

siloxy)5-prostenoic acid methyl ester (7). A 12-L three-

neck round-bottom ﬂask was charged sequentially with

THF (3 L), bis(2,2,2-triﬂuoroethyl) (methoxycarbonyl)-

methylphosphonate (123 mL, 583 mmol), and pre-dried

(over 4 A molecular sieves for 1 week) tris [2-(2-meth-

oxyethoxy)ethyl]amine (TDA-1; 561 mL, 1.75 mol). The

brown solution was cooled to À65 ^ꢀC (internal tem-

perature) and KN(SiMe₃)₂(1.166 L of a 0.5 M solution

in toluene, 583 mmol) was added over 40 min while

maintaining the internal temperature below À50 ^ꢀC. The

mixtuer was stirred for one h at an internal temperature

of À65 ^ꢀC before a solution of aldehyde 6 (301 g,

530 mmol) in THF (1.5 L) was added over 40 min while

A 12-L three-neck round-bottom ﬂask was charged with

a solution of the above-synthesized alcohol (542 g,

911 mmol) in THF (5 L). The solution was cooled to

0 ^ꢀC and a 1 M solution of TBAF in THF (1.275 L,

1.275 mol) was added over 10 min. The reaction was

stirred at 0 ^ꢀC for 1 h and was quenched by the addition

2040

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

of saturated NH₄Cl (5 L). The solution was extracted with

ethyl acetate (2ꢂ4 L) and the combined organic phases

were washed with saturated NaCl, dried over Na₂SO₄, ﬁl-

tered, and concentrated. The residue was puriﬁed by

chromatography on 4 kg of silica gel eluting with 50%

ethyl acetate in hexane!100% ethyl acetate gradient to

aﬀord diol 8 (348 g, 86%). MS, m/z at 503 for (M+Na)⁺.

removed, ice (1.8 kg) was added, and the mixture was

stirred for 30 min before the phases separated. The

aqueous layer was extracted with ethyl acetate (2ꢂ2 L)

and the combined organic layers were washed with

saturated NaCl (4 L), dried over Na₂SO₄, ﬁltered, and

concentrated to provide an oil. A stirred suspension of

the oil in 3:1 v:v acetic acid:water (4.65 L) was heated to

65 ^ꢀC for 3.5 h. The suspension was cooled to room

temperature and poured into water (18 L), and the mix-

ture was extracted with ethyl acetate (3ꢂ4 L). The com-

bined organic layers were washed with saturated

NaHCO₃to pH 7–8 and then with saturated NaCl,

dried over Na₂SO₄, ﬁltered, and concentrated to aﬀord

an impure sample of AL–6598 (245 g) as a golden oil.

(5Z)-(9S,11R,15R)-11,15-Bis(tetrahydropyran-2-yloxy)-

15-cyclohexyl-9-hydroxy-3-oxa-16,17,18,19,20-pentanor-

5-prostenoic acid t-butyl ester (9). A 12-L three-neck

round-bottom ﬂask was charged with n-Bu₄NHSO₄

(105.4 g, 320 mmol) and a solution of diol 8 (347 g,

720 mmol) in toluene (3.5 L). Sequential addition of

t-butylbromoacetate (190 mL, 1.28 mol) and aqueous

NaOH (2.542 L, prepared by the dilution of 1.116 L of

50% w/w NaOH with 1.426 L of water; 14 mol) was

followed by stirring for 40 min. Saturated NH₄Cl (5 L)

was then added, and the phases were separated. The

aqueous layer was extracted with toluene (2ꢂ1.5 L) and

the combined organic phases were washed with satu-

rated NaCl (3 L), dried over Na₂SO₄, ﬁltered, and con-

centrated. The residue was puriﬁed by chromatography

on 7 kg of silica gel eluting with a gradient of 30% to

50% ethyl acetate in hexane to aﬀord ester 9 (353.3 g,

82%) as well as some impure material, which was re-

puriﬁed by chromatography under the same conditions to

aﬀord additional 9 (18 g; total=371.3 g=86%). ¹H NMR

(200MHz, CDCl₃) d 5.65 (m, 2H), 4.62 (m, 2H), 4.16 (m,

1H), 4.10–3.75 (m, 3H), 3.95 (s, 2H), 3.45 (m, 2H), 2.50–

0.90 (broad m, 35H), 1.46 (s, 9H). HRMS, m/z calcd for

C₃₄H₅₉O₈[(M+H)⁺], 595.4209; found, 595.4208.

The oil was puriﬁed by chromatography on 7 kg of silica

gel eluting with 40% hexane in t-butyl methyl ether to

aﬀord ﬁve 25–30 g fractions containing various ratios of

AL–6598 to the Á^5,6,8,9diene elimination by-product

(total, 160 g). These fractions were puriﬁed by HPLC

TM

using a CHIRALPAK¹AD 10 cm diameterꢂ50 cm

length column eluting with 9:1 v/v hexane/2-propanol

using a 200 mL/min ﬂowrate. The total amount of AL–

6598 isolated after drying to a constant weight was

136.5 g (54% from alcohol 10), with an average purity

1

of 99% as measured by analytical HPLC. H NMR d

5.67 (m, 2H), 5.08 (sep, J=6 Hz, 1H), 4.30–3.95 (m,

6H), 3.40 (m, 1H), 2.35 (m, 2H), 2.30–2.00 (m, 3H),

1.93–1.35 (m, 12H), 1.25 (d, J=6 Hz, 6H), 1.22–0.90 (m,

6H); ¹³C NMR d 170.21 (C), 131.74 (CH), 126.77 (CH),

75.69 (CH), 75.25 (CH), 68.73 (CH), 67.64 (CH₂), 66.70

(CH₂), 61.20 (CH), 54.23 (CH), 51.20 (CH), 44.44 (CH),

43.65 (CH), 31.64 (CH₂), 30.17 (CH₂), 30.08 (CH₂),

29.32 (CH₂), 28.01 (CH₂), 26.50 (CH₂), 26.27 (CH₂),

26.16 (CH₂), 21.78 (CH₃). HRMS, m/z calcd for

C₂₃H₄₀O₅Cl [(M+H)⁺], 431.2564; found, 431.2569.

(5Z)-(9S,11R,15R)-11,15-Bis(tetrahydropyran-2-yloxy)-

15-cyclohexyl-9-hydroxy-3-oxa-16,17,18,19,20-pentanor-

5-prostenoic acid isopropyl ester (10). A 12-L three-

neck round-bottom ﬂask was charged with a solution

of t-butyl ester 9 (350 g, 588 mmol) in 2-propanol

(3.5 L). Titanium (IV) isopropoxide (261 mL, 880 mmol)

was added at room temperature and the mixture was

reﬂuxed for 1 h. The reaction mixture was then cooled

in an ice bath and was treated with a saturated solution

of sodium potassium tartrate tetrahydrate (5 L). The

solution was extracted with ethyl acetate (4ꢂ2 L), the

combined organic phases were washed with saturated

NaCl (5 L), dried over Na₂SO₄, ﬁltered, and con-

centrated, and the residue was puriﬁed by chromato-

graphy on 7 kg of silica gel eluting with a 20–50% ethyl

acetate in hexane gradient to aﬀord isopropyl ester 10

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

tert-butyl ester (32). Alcohol 9 (280 mg, 0.47 mmol) was

dissolved in 4.0 mL of a 61:1.2:1.0 v:v:v mixture of

CH₃CN/CCl₄/pyridine and then PPh₃(180 mg,

0.70 mmol) was added. The reaction was stirred for 17 h

was then treated with 1:1 ether/hexane (10 mL). The

suspension was ﬁltered, the ﬁltrate was concentrated,

and the residue was puriﬁed by chromatography on silica

gel eluting with 40% ether in hexane to aﬀord the 9b

chloride (5Z)-(9R,11R,15R)-11,15-bis(tetrahydropyran-

2-yloxy)-9-chloro-15-cyclohexyl-3-oxa-16,17,18,19,20-

pentanor-5-prostenoic acid tert-butyl ester (90 mg, 34%;

R_f0.47, 40% ether in hexane) free from the Á^5,6,8,9

diene by-product.

1

(329.8 g, 96%). H NMR (characteristic peaks only) d

5.80–5.52 (m, 2H), 5.15 (sep, J=6 Hz, 1H), 4.03 (broad

s, 2H), 1.27 (d, J=6 Hz, 6H).

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

isopropyl ester (AL-6598). To a 0 ^ꢀC solution of alcohol

10 (340 g, 585 mmol) in pyridine (3.4 L) was added

methanesulfonyl chloride (91.5 mL, 1.18 mol). The

reaction mixture was stirred at 0 ^ꢀC for 15 min and at

room temperature for 4 h, at which time n-Bu₄NCl

(2.5 kg, 8.99 mol) and toluene (5.2 L) were added. After

stirring at room temperature for 16 h the suspension was

heated at 55 ^ꢀC for 6 h. The heating source was

A solution of this compound (80 mg, 0.13 mmol) in 65%

aqueous acetic acid (7 mL) was heated at 65–70 ^ꢀC for

45 min. The reaction was cooled to room temperature

and was concentrated. The residue was dissolved in

anhydrous ethanol and was concentrated, and the resi-

due puriﬁed by chromatography on silica gel eluting

with 40% hexane in ethyl acetate to aﬀord 32 (60 mg,

100%; R_f0.4, 40% hexane in ethyl acetate). ¹H NMR d

5.69 (m, 2H), 4.32–3.85 (m, 5H), 3.38 (m, 1H), 2.50–1.95

(m, 5H), 1.95–0.80 (br m, 29H), 1.43 (s, 9H); ¹³C NMR

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2041

d 169.9 (C), 131.7 (CH), 126.8 (CH), 82.0 (C), 75.6

(CH), 75.1 (CH), 67.9 (CH₂), 66.6 (CH₂), 54.2 (CH),

51.0 (CH), 44.3 (CH), 43.7 (CH), 31.4 (CH₂), 30.3

(CH₂), 30.1 (CH₂), 29.3 (CH₂), 28.1 (CH₂), 28.0 (CH₂),

26.5 (CH₂), 26.3 (CH₂), 26.1 (CH₃). HRMS, m/z calcd

for C₂₄H₄₂O₅Cl [(M+H)⁺], 445.2720; found, 445.2716.

diameter, 45 mg/cm:1.5 cm, 9.7 mg-atom) was added in

0.3 cm pieces to a stirred 0 ^ꢀC (internal temperature)

solution of 4,4⁰-di-t-butylbiphenyl (2.66 g, 10.0 mmol)

and 5 mg of 2,2⁰-bipyridyl in dry THF (20 mL) under

Ar. The mixture was titrated to a red endpoint with n-

BuLi (2.5 M in hexane, 0.12 mL) and stirred for 15 h to

form a deep blue-green solution of lithium 4,4⁰-di-t-

butylbiphenyl. The solution was cooled to À45 ^ꢀC

(internal temperature) and a solution of chloride 13

(1.12 g, 4.5 mmol) in hexane (9.0 mL, pre-dried over 4 A

molecular sieves) was added dropwise via syringe, keeping

the internal temperature below À40^ꢀC. A yellow-green

endpoint was observed. After 5 min, a solution of 0.25M

lithium (2-thienyl)cyanocuprate (20 mL, 5.0 mmol) was

added dropwise while maintaining the internal tempera-

ture below À40^ꢀC. A cherry-red endpoint was observed.

After 10min a solution of (4R)-4-(t-butyldimethylsiloxy)-

2 - [(diethylamino)methyl]cyclopent - 2 - en - 1 - one (14,¹³

1.12 g, 3.77 mmol) in dry THF (20 mL) was added

dropwise while maintaining the internal temperature

below À40 ^ꢀC. The solution was allowed to warm to

À20 ^ꢀC and was then quenched into a rapidly stirring

mixture of diethyl ether and saturated NH₄Cl. After

several hours, the phases were separated and the aqu-

eous layer was extracted with ethyl acetate. The com-

bined organic phases were dried (MgSO₄), ﬁltered, and

concentrated, and the residue was puriﬁed by chroma-

tography on 200 g of silica gel eluting with a gradient of

1:9 to 1:3 ethyl acetate/hexane to aﬀord conjugate

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

(AL-6556). A solution of 32 (133 mg, 0.299 mmol),

methanol (20 mL), water (2.0 mL), and lithium hydrox-

ide monohydrate (50 mg, 1.2 mmol) was stirred for 17 h

and was then added to 75 mL of 2:1 CHCl₃/0.1 M HCl.

The layers were separated, the aqueous phase was

extracted with CHCl₃(3ꢂ25 mL), and the combined

organic layers were dried (Na₂SO₄) and concentrated to

aﬀord AL-6556 (99 mg, 85%). ¹³C NMR d 173.17 (C),

132.77 (CH), 126.03 (CH), 75.68 (CH), 75.24 (CH), 66.89

(CH₂), 66.40 (CH₂), 61.32 (CH), 54.12 (CH), 50.62 (CH),

43.95 (CH₂), 43.33 (CH), 30.92 (CH₂), 30.73 (CH₂),

29.89 (CH₂), 29.30 (CH₂), 27.95 (CH₂), 26.44 (CH₂),

26.25 (CH₂), 26.09(CH₂). HRMS, m/z calcd for

C₂₀H₃₄O₅Cl [(M+H)⁺], 389.2094; found, 389.2090.

(1R)-3-Chloro-1-cyclohexylpropanol (12). A solution of

(1R)-3-chloro-1-phenylpropanol^15b(11; 4.25 g, 25 mmol)

in methanol (20 mL) containing 5% w/w Rh/Al₂O₃

(750 mg) was hydrogenated at 60–65 psig on a Parr

shaker for 6.5 h. The solution was diluted with ethyl

acetate, ﬁltered, and concentrated. The residue (4.0 g of

an oil) consisted of a 61:37:2 ratio of 12, 1-chloro-3-

cyclohexylpropane (deoxy-12), and (1R)-1-cyclohexyl-

propanol (deschloro-12) [diagnostic ¹H NMR signals

(DMSO-d₆): for 12, d 3.30 (m, 1H), 3.68 (2 overlapping

t, J=5.2 Hz, and 7.0 Hz, 2H), 4.48 (d, J=5.9 Hz, 1H,

exchanges with D₂O); for deoxy-12, d 3.58 (t, J=6.6 Hz,

2H); for deschloro-12, d 0.83 (t J=7 Hz, 3H), 3.05 (m,

1H), 4.12 (d, J=5.9 Hz, 1H, exchanges with D₂O)].

Chromatographic puriﬁcation of this oil on 150 g of

silica gel eluting with 25% ethyl acetate in hexane aﬀor-

ded 12 (2.32 g, 55%) containing 2–3% of deschloro-12.

HPLC analysis (Chiralcel OD, 250ꢂ4.6 mm, 95:5 hex-

ane–i-PrOH) of the benzoate of 12 showed 97.6% ee.

1

addition product 15 (950 mg, 58%). H NMR d 6.08 (s,

1H), 5.32 and 5.29 (both s, 2:3 ratio, total 1H), 4.68 (2

overlapping q, J=5.2 Hz, 1H), 4.12 (pentet, J=5.2 Hz,

1H), 3.55 (m, 2H), 3.30 (br q, J=4 Hz, 1H), 2.65 (br s,

1H), 2.62 (d of d, J=17.8 Hz, 5.8 Hz, 1H), 2.30 (d of d,

J=18.0 Hz, 4.6 Hz, 1H), 1.30 and 1.29 (2 overlapping q,

J=5.3 Hz, 3H), 1.20 and 1.17 (2 overlapping q,

J=7 Hz, 3H), 1.9–0.8 (m, 15H), 0.87 (s, 9H), 0.08 (s,

3H), 0.06 (s, 3H).

[3R(1E,3R),4R]-3-(3-Cyclohexyl-3-hydroxypropyl)-4-(t-

butyldimethylsiloxy)-2-methylenecyclopentanone

(16).

PPTS (250 mg, 1.0 mmol) was added to a solution of 15

(3.2 g, 7.3 mmol) in 1:1 diethyl ether/i-PrOH (100 mL).

After 2 h the solution was added to saturated NaHCO₃

and was extracted with diethyl ether and ethyl acetate.

The combined organic layers were washed with water

and saturated NaCl, dried (MgSO₄), ﬁltered, and con-

centrated, and the residue was puriﬁed by chromato-

graphy on 200 g of silica gel eluting with 25% ethyl

(1R)-3-Chloro-1-cyclohexylprop-1-yl 1-ethoxyethyl ether

(13). Ethyl vinyl ether (EVE; 10 mL) was added to a

stirred ice-cooled solution of alcohol 12 (4.89 g,

27.7 mmol) and pyridinium p-toluenesulfonate (PPTS;

40 mg, 0.16 mmol) in CH₂Cl₂(40 mL, pre-dried over 4 A

molecular sieves). After 10 min a further 200 mg

(0.8 mmol) of PPTS and 8 mL of EVE were added, and

the solution was allowed to warm to room temperature.

After 1 h, the solution was ﬁltered through a 2.5 cm pad

of silica gel (slurried with diethyl ether) on a 350 mL

fritted funnel, eluting with diethyl ether. Concentration

aﬀorded 13 (6.69 g, 97%). ¹H NMR d 4.7 (2 overlapping

q, J=5.3 Hz, 1H), 3.4–3.8 (m, 5H), 1.32 and 1.30 (2

overlapping d, J=5.3 Hz, 3H), 1.21 (t, J=7 Hz, 3H),

2.0–0.9 (m, 13H).

1

acetate in hexane to aﬀord alcohol 16 (2.05 g, 77%). H

NMR (DMSO-d₆) d 5.83 (s, 1H), 5.30 (s, 1H), 4.21 (d,

J=5.5 Hz, 1H, exchanges with D₂O), 4.12 (br q,

J=5 Hz, 1H), 3.10 (br s, 1H), 2.65 (d of d, J=18 Hz,

6 Hz, 1H), 2.11 (d of d, J=18 Hz, 5 Hz, 1H), 1.8–0.8 (m,

15H), 0.79 (s, 9H), 0.01 (s, 3H), 0.00 (s, 3H); ¹³C NMR

(DMSO-d₆) d 203.89, 147.79, 117.36, 73.83, 71.74,

50.48, 46.34,43.35, 30.81, 28.92, 28.18, 27.66, 26.24,

25.99, 25.85, 25.62, 17.62,À4.64,À4.94.

[3R(1E,3R),4R]-3-[3-Cyclohexyl-3-(t-butyldimethylsilox-

y)propyl]-4-(t-butyldimethylsiloxy)-2-methylenecyclopen-

tanone (17). To an ice-cooled solution of alcohol 16

(1.53 g, 4.2 mmol) in a 4:3 mixture of CH₂Cl₂/DMF

[3R(1E,3R),4R]-3-[3-Cyclohexyl-3-[(3-oxapent-2-yl)oxy]-

propyl]-4-(t-butyldimethylsiloxy)-2-methylenecyclopenta-

none (15). Lithium wire (1% Na content, 3.2 mm

2042

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

(35 mL) under Ar was added via syringe ⁱPrNEt₂

(1.5 mL, 8.6 mmol), followed by BuMe₂SiOTf (2.0 mL,

(5Z)-(9S,11R,15R)-15-Cyclohexyl-11,15-di-t-butyldime-

thylsiloxy - 9 - hydroxy - 2,3,4,16,17,18,19,20 - octanor - 5 -

prosten-1-ol (20). l-Selectride¹(1.0 M in THF, 2.5 mL,

2.5 mmol) was added dropwise to a À78 ^ꢀC solution of

ketone 19 (1.10 g, 1.62 mmol) in dry THF (10 mL) under

Ar. After 45 min the cooling bath was removed and the

solution was allowed to warm to room temperature and

then cooled to 0 ^ꢀC. Careful addition of 30% H₂O₂

(2 mL) was followed by warming of the solution to

room temperature. Normal phase tlc analysis (12%

ethyl acetate in hexane) showed the presence of a major,

higher R_fspot and a minor, lower R_fspot, assigned as

the 9a and 9b alcohols, respectively.²⁵The mixture was

added to saturated NH₄Cl and extracted with ethyl

acetate and ether, and the combined organic layers were

washed with 2 M Na₂S₂O₃, water, and saturated NaCl,

dried (MgSO₄), ﬁltered, and concentrated. The residue

was puriﬁed by chromatography on 75 g of silica gel

eluting with 12% ethyl acetate in hexane to aﬀord the

9a alcohol (5Z)-(9S,11R,15R)-15-Cyclohexyl-11,15-di-t-

butyldimethylsiloxy - 9 - hydroxy - 2,3,4,16,17,18,19,20 -

octanor-5-prosten-1-yl 3-oxapent-2-yl ether (560 mg,

56%). ¹H NMR (DMSO-d₆) 5.5 (m, 2H), 4.62 (q,

J=5.3 Hz, 1H), 4.30 (d, J=5.2 Hz, 1H, exchanges with

D₂O), 4.1–3.3 (m, 7H), 2.1 (septet, J=7 Hz, 2H), 1.8–

0.8 (m, 19H), 1.17 (d, J=5.3 Hz, 3H), 1.08 (t, J=7 Hz,

3H), 0.84 (s, 9H), 0.83 (s, 9H), 0.00 (s, 12H).

t

8.7 mmol). After 1.5 h, the mixture was diluted with

diethyl ether and washed with water, saturated

KH₂PO₄, and saturated NaCl. The organic layer was

dried (MgSO₄), ﬁltered, and concentrated, and the resi-

due was puriﬁed by chromatography on 100 g of silica

gel eluting with 10% diethyl ether in hexane to aﬀord

bissilyl ether 17 (1.60 g, 80%). ¹H NMR d 6.08 (d,

J=2.2 Hz, 1H), 5.28 (d, J=1.5 Hz, 1H), 4.09 (q,

J=5.7 Hz, 1H), 3.40 (br q, J=5 Hz, 1H), 2.63 (br s,

1H), 2.62 (d of d, J=18 Hz, 6 Hz, 1H), 2.30 (d of d,

J=18 Hz, 5 Hz, 1H), 1.8–0.9 (m, 15H), 0.88 (s, 18H),

0.08 (s, 3H), 0.06 (s, 3H), 0.03 (s, 3H), 0.02 (s, 3H); ¹³C

NMR d 204.54, 147.59, 117.99, 76.43, 72.29, 51.29,

46.89, 43.14, 30.58, 28.67, 28.54, 27.78, 26.73, 26.51,

25.94, 25.73, 18.14, 17.95,À4.24,À4.36,À4.46,À4.79.

Z-3-(Tri-n-butylstannyl)-2-propen-1-yl (1⁰-ethoxy)ethyl

ether (18). Pyridinium p-toluenesulfonate (1.00 g,

4.0 mmol) was added to a stirred solution of Z-3-(tri-n-

butylstannyl)-2-propen-1-ol^18b(3.18 g, 9.17 mmol) in

32 mL of ethyl vinyl ether and 16 mL of dichloro-

methane under argon. The mixture was stirred at 25 ^ꢀC

for 4 h, and then diluted with 40 mL of 9:1 (v/v) hexane–

ethyl acetate. The suspension was decanted onto a pad

of silica gel and eluted with 9:1 (v/v) hexane–ethyl ace-

tate. Concentration in vacuo aﬀorded 3.21 g (84%) of

18 as an oil: H NMR (CDCl₃) d 0.85–1.1 (m, 15H),

To a 0 ^ꢀC solution of the above alcohol (550 mg,

0.90 mmol) in 1:1 diethyl ether/ⁱPrOH (16 mL) was

added PPTS (40 mg, 0.16 mmol). The mixture was

warmed to room temperature and stirred for 8 h. The

solution was partitioned between ethyl acetate and

saturated NaHCO₃, the organic phase was dried

(MgSO₄), ﬁltered, and concentrated, and the residue

was puriﬁed by chromatography on 50 g of silica gel

eluting with 25% ethyl acetate in hexane to provide diol

1

1.21 (t, J=7, 3H), 1.35 (d, J=5.5, 3H), 1.1–1.7 (m,

12H), 3.41–3.73 (m, 2H), 3.85–4.15 (m, 2H), 4.75 (q,

J=5.5, 1H), 6.06 (dt, J=13, 1, 1H, J_Sn-H=64), 6.63 (dt,

J=13, 4, 1H, J_Sn-H=134); ¹³C NMR (CDCl₃) d 13.7,

15.3, 19.8 (CH₃), 10.5 (J_119Sn-C=343, J_117Sn-C=328),

27.3 (J_Sn-C=56), 29.2 (J_Sn-C=21), 60.6, 67.9 (J_Sn-C=38)

(CH₂); 99.2, 131.5 (J_119Sn-C=366, J_117Sn-C=350), 144.4

(CH). Note: ¹¹⁷Sn (7.6%) and ¹¹⁹Sn (8.6%) satellites are

unresolved except as indicated.

1

20 (370 mg, 76%). H NMR d 5.80 (br q, J=9 Hz, 1H),

5.56 (d of t, J=10.6 Hz, 4.6 Hz, 1H), 4.39 (t, J=10.2 Hz,

1H), 4.05 (d, J=17 Hz, 2H), 3.81 (d, J=6 Hz, 1H), 3.4

(br s, 2H), 3.38 (br q, J=4.7 Hz, 1H), 2.70 (q,

J=11.7 Hz, 1H), 2.05 (br d, J=11.7 Hz, 1H), 1.9–0.7

(m, 19H), 0.88 (s, 18H), 0.07 (s, 3H), 0.02 (s, 3H). ¹³C

NMR d 132.58, 129.09, 80.26, 76.46, 75.29, 57.34, 52.13,

42.97, 41.74, 32.15, 29.81, 28.71, 28.64, 27.88, 26.73,

26.55, 26.48, 25.95, 25.75, 18.19, 17.79, À4.21, À4.34,

À4.71.

(5Z)-(11R,15R)-15-Cyclohexyl-11,15-di-t-butyldimethyl-

siloxy-9-oxo-2,3,4,16,17,18,19,20-octanor-5-prosten-1-yl

3-oxapent-2-yl ether (19). Methylithium (1.0 M in 9:1

cumene/THF, 0.80 mL, 0.80 mmol) was added dropwise

to an ice-cooled suspension of CuCN powder (36 mg,

0.40 mmol) in dry THF (1.0 mL). After 5 min Z-

Bu₃SnCH¼CHCH₂OCH(CH₃)OCH₂CH₃(18; 160 mg,

0.38 mmol) was added dropwise (0.5 mL of dry THF to

rinse). The solution was allowed to warm to room tem-

perature and was stirred for 1.5 h, then cooled to

À78 ^ꢀC. A solution of enone 17 (110 mg, 0.23 mmol) in

dry THF (0.9 mL) was added dropwise. After 10 min,

the mixture was added to saturated NH₄Cl and stirred

for several hours. The solution was extracted with ethyl

acetate, dried (MgSO₄), ﬁltered, and concentrated, and

the residue was puriﬁed by chromatography on 60 g of

silica gel eluting with 10% ethyl acetate in hexane to

(5Z)-(9S,11R,15R)-15-Cyclohexyl-11,15-di-t-butyldi-

methylsiloxy-9-hydroxy-3-oxa-16,17,18,19,20-pentanor-5-

prostenoic acid isopropyl ester (21). Ice-cold 25%

NaOH (3.5 mL) was added to a vigorously stirring, ice-

cooled solution of diol 20 (340 mg, 0.63 mmol) and

n-Bu₄HSO₄(21 mg, 0.06 mmol) in toluene (3.5 mL).

t-Butyl bromoacetate (0.25 mL, 1.7 mmol) was added

dropwise and the solution was allowed to warm to room

temperature over 1 h. The mixture was diluted with die-

thyl ether, washed with water and saturated KH₂PO₄,

dried (MgSO₄), ﬁltered, and concentrated. The residue

was puriﬁed by chromatography on 25 g of silica gel elut-

ing with 12% ethyl acetate in hexane to aﬀord the O-alky-

lated product (5Z)-(9S,11R,15R)-15-cyclohexyl-11,15-di-t-

butyldimethylsiloxy-9-hydroxy-3-oxa-16,17,18,19,20-pen-

1

aﬀord 19 (100 mg, 72%). H NMR d 5.6 (m, 2H), 4.72

(q, J=5.3 Hz, 1H), 4.1 (m, 3H), 3.6 (m, 2H), 3.39 (br q,

J=5 Hz, 1H), 2.42 (br t, J=5.7 Hz, 2H), 2.59 (d of d,

J=18 Hz, 6 Hz, 1H), 2.15 (d of d, J=18 Hz, 5 Hz, 1H),

1.9 (br s, 2H), 1.31 (t, J=5.3 Hz, 3H), 1.21 (t, J=7 Hz,

3H), 1.8–0.9 (m, 15H), 0.89 (s, 18H), 0.08 (s, 3H), 0.05

(s, 3H), 0.03 (s, 3H), 0.02 (s, 3H).

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2043

1

tanor-5-prostenoic acid t-butyl ester (320 mg, 78%). H

NMR d 5.65 (m, 2H) 4.20 (d, J=6 Hz, 2H), 4.05 (m,

2H), 3.96 (s, 2H), 3.38 (br q, J=5 Hz, 1H), 3.30 (d,

J=11 Hz, 1H, exchanges with D₂O), 2.4 (m, 1H), 2.2

(m, 1H), 1.48 (s, 9H), 1.9–0.8 (m, 19H), 0.88 (s, 18H),

0.08 (s, 6H), 0.02 (s, 6H).

calcd for C₂₃H₃₈O₅Cl [(M+H)⁺], 429.2408; found,

429.2389.

(5Z,13E)-(11R,15S)-15-cyclohexyl-11,15-dihydroxy-3-

oxa-16,17,18,19,20-pentanor-5,13-prostadienoic acid iso-

propyl ester (45). To a vigorously stirring mixture of

alcohol 23 (1.09 g, 1.84 mmol; synthesized analogously

to its 13,14-dihydro congener 9) and pyridine (11 mL) at

0 ^ꢀC was added methanesulfonyl chloride dropwise

(510 mg, 4.5 mmol). The reaction was stirred for 30 min

at 0 ^ꢀC and for 2 h at room temperature. Saturated

NH₄Cl (40 mL) was added and the mixture was extrac-

ted with ethyl acetate (2ꢂ40 mL). The combined organic

layers were dried over MgSO₄, ﬁltered, and concentrated,

and the residue was puriﬁed by chromatography on silica

gel eluting with 1:1 hexane/ethyl acetate to aﬀord the

corresponding 9a mesylate (5Z,13E)-(9S,11R,15S)-11,15-

bis(tetrahydropyran-2-yloxy)-15-cyclohexyl-9-(methane-

sulfonyloxy)-3-oxa-16,17,18,19,20-pentanor-5-prostenoic

acid isopropyl ester (1.08 g, 87%, R_f0.5 in 1:1 hex-

ane:ethyl acetate).

To a solution of the above t-butyl ester (100 mg,

0.153 mmol) in i-PrOH (6 mL) under Ar was added

Ti(OPrⁱ)₄(0.2 mL). The solution was heated to 65–70 ^ꢀC

for 2 h and to reﬂux for 30 min, then cooled in ice,

quenched with saturated sodium potassium tartrate,

and extracted with diethyl ether. The organic phase was

dried (MgSO₄), ﬁltered, and concentrated. The residue

was combined with the crude product from another run

of 1/2 of the above scale and the whole was puriﬁed by

chromatography on 20 g of silica gel eluting with 15%

ethyl acetate in hexane to aﬀord isopropyl ester 21

1

(110 mg, 75%). H NMR d 5.6 (m, 2H), 5.08 (septet,

J=6.3 Hz, 1H), 4.19 (d, J=6 Hz, 2H), 4.03 (br s, 1H),

4.02 (s, 2H), 3.95 (br s, 1H), 3.33 (br q, J=5 Hz, 1H),

3.3 (br s, 1H, exchanges with D₂O), 2.4 (m, 1H), 2.2 (m,

2H), 1.8–0.7 (m, 19H), 1.24 (d, J=6.3 Hz, 6H), 0.86 (s,

18H), 0.05 (s, 6H), 0.01 (s, 3H), 0.00 (s, 3H).

To a THF (11 mL) solution of the mesylate at 0 ^ꢀC was

added dropwise a 1 M solution of LiEt₃BH in THF

(11 mL, 11 mmol) and the reaction was stirred overnight

at room temperature. The mixture was poured into a 1:1

v/v mixture of ethyl acetate/saturated NH₄Cl (50 mL),

the layers were separated, and the aqeuous phase was

extracted with ethyl acetate (2ꢂ30 mL). The combined

organic layers were dried over MgSO₄, ﬁltered, and

concentrated, and the residue was puriﬁed by chroma-

tography on a silica gel eluting with 40% ethyl acetate

in hexane to aﬀord the 9-deoxy alcohol (5Z,13E)-

(11R,15S)-11,15-bis(tetrahydropyran-2-yloxy)-15-cyclo-

hexyl-3-oxa-16,17,18,19,20-pentanor-5,13-prostadienol

(24; 642 mg, 79%, R_f0.4 in 40% ethyl acetate in

hexane).

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

isopropyl ester (AL-6598). Methanesulfonyl chloride

(0.05 mL, 0.65 mmol) was added to a 0 ^ꢀC solution of

alcohol 21 (110 mg, 0.17 mmol) in pyridine (pre-dried

over 4 A molecular sieves, 1.0 mL) under Ar. The solu-

tion was allowed to warm to room temperature over

.

2.5 h. A suspension of Bu₄NCl H₂O (1.0 g, 3.4 mmol) in

toluene (1.5 mL) was added and the resulting mixture

stirred at 55 ^ꢀC overnight. The mixture was added to ice

water and extracted with diethyl ether and the organic

phase was washed with saturated NaCl, dried (MgSO₄),

ﬁltered, and concentrated. The residue was dissolved in

THF (3 mL) and cooled to 0 ^ꢀC. A premixed solution of

THF (1.5 mL) and 48% HF (1.5 mL) was added drop-

wise. The solution was allowed to warm to room tem-

perature over several hours until TLC analysis indicated

complete desilylation. The mixture was added to satu-

rated NaHCO₃and extracted with ethyl acetate. The

organic phase was dried (MgSO₄), ﬁltered, and con-

centrated, and the residue was puriﬁed by chromato-

graphy on 15 g of silica gel eluting with 50% ethyl

acetate in hexane to aﬀord 45.4 mg (63%, calculated as

the chloride) of AL–6598 and its 9-deschloro-Á^5,6,8,9

diene by-product as a 3.5:1 molar mixture as measured

To a solution of the above (560 mg, 1.12 mmol) in DMF

(5 mL) was added PDC (1.32 g, 3.51 mmol). After 48 h,

water (20 mL) was added and the mixture was extracted

with ethyl acetate (4ꢂ20 mL). The combined organic

layers were dried over Na₂SO₄, ﬁltered, and con-

centrated. The residue was dissolved in acetone (20 mL)

and DBU (780 mg, 5.12 mmol) was added. After 15 min

isopropyl iodide (850 mg, 5.0 mmol) was added and the

reaction was stirred for 20 h. Concentration of the mix-

ture and chromatography of the residue on silica gel

eluting with 20% ethyl acetate in hexane aﬀorded

(5Z,13E)-(11R,15R)-11,15-bis(tetrahydropyran-2-yloxy)-

15-cyclohexyl-3-oxa-16,17,18,19,20-pentanor-5,13-pros-

tadienoic acid isopropyl ester (238 mg, 38% R_f0.4 in

20% ethyl acetate in hexane).

1

by H NMR spectroscopy (characteristic resonance for

H-9 of the diene, d=5.3 ppm).

(5Z,13E)-(9R,11R,15S)-9-Chloro-15-cyclohexyl-11,15-di-

hydroxy-3-oxa-16,17,18,19,20-pentanor-5,13-prostadie-

noic acid isopropyl ester (25). Beginning with lactone 3,

the title compound was synthesized analogously to AL–

6598 in 9 steps and 2.6% yield. ¹³C NMR d 170.04 (C),

134.51 (CH), 132.64 (CH), 130.43 (CH), 127.58 (CH),

77.34 (CH), 75.40 (CH), 68.60 (CH), 67.60 (CH₂), 66.64

(CH₂), 59.64 (CH), 55.95 (CH), 53.36 (CH), 43.61 (CH),

43.57 (CH₂), 28.83 (CH₂), 28.70 (CH₂), 26.49 (CH₂),

26.06 (CH₂), 25.99 (CH₂), 21.82 (CH₃). HRMS, m/z

To a mixture of the above, bis THP ether (230 mg,

0.41 mmol), i-PrOH (18 mL), and water (2 mL) was

added 12 M HCl (1 mL). After 2 h saturated NaHCO₃

(20 mL) was added and the mixture was extracted with

ethyl acetate (3ꢂ20 mL), dried over MgSO₄, ﬁltered,

and concentrated. The residue was puriﬁed by chroma-

tography on a 25 cm tallꢂ26 mm diameter silica gel col-

umn eluting with 40% hexane in ethyl acetate to aﬀord

9-deoxy ester 45 (120 mg, 74%, R_f0.25 in 40% hexane

2044

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

in ethyl acetate). ¹³C NMR d 170.00 (C), 134.17 (CH),

132.73 (CH), 125.97 (CH), 77.92 (CH), 77.68 (CH), 68.47

(CH), 67.38 (CH₂), 66.73 (CH₂), 58.02 (CH), 43.44 (CH),

42.77 (CH), 32.15 (CH₂), 28.89 (CH₂), 28.80 (CH₂),

27.63 (CH₂), 26.51 (CH₂), 26.06 (CH₂), 25.94 (CH₂),

21.97 (CH₃). HRMS, m/z calcd for C₂₃H₃₇O₅

[(M+H)⁺]. 393.2641; found, 393.2633.

A 0 ^ꢀC solution of the above compound (140 mg,

0.25 mmol), methanol (10 mL), and water (0.5 mL) was

treated with saturated HCl (10 drops). After 15 min the

temperature was raised to room temperature. After an

additional 30 min, NaHCO₃was added to quench the

reaction, and the mixture was partitioned between

CHCl₃and saturated NaHCO₃. The organic layer was

dried (Na₂SO₄), ﬁltered, and concentrated, and the

residue was puriﬁed by chromatography on silica gel

eluting with 50–100% ethyl acetate in hexane gradient

to aﬀord the deprotection product (5Z)-(11R,15R)-15-

cyclohexyl-11,15-dihydroxy-3-oxa-16,17,18,19,20-penta-

nor-5-prostenoic acid methyl ester (86 mg, 95%; R_f

0.16, 1:1 ethyl acetate/hexane).

(5Z,13E)-(11R,15S)-15-cyclohexyl-11,15-dihydroxy-3-

oxa-16,17,18,19,20-pentanor-5,13-prostadienoic acid (22).

A solution of 45 (61 mg, 0.15 mmol), lithium hydroxide

monohydrate (60 mg, 1.43 mmol), methanol (1.1 mL),

and water (0.5 mL) was stirred for 16 h. The reaction

was quenched by the addition of 1 M HCl (5 mL) and

was extracted with ethyl acetate (3ꢂ10 mL), dried over

Na₂SO₄, ﬁltered, and concentrated to aﬀord 22 (43 mg,

81%). ¹³C NMR d 173.44 (C), 134.03 (CH), 133.63 (CH),

125.38 (CH), 78.00 (CH), 77.74 (CH), 66.31 (CH₂), 57.76

(CH), 43.22 (CH), 42.88 (CH), 32.14 (CH₂), 28.89 (CH₂),

28.77 (CH₂), 27.59 (CH₂), 26.48 (CH₂), 26.03 (CH₂),

25.97 (CH₂). MS, m/z calcd for C₂₀H₃₃O₅[(M+H)⁺],

353.2328; found, 353.2326.

A

solution of the above methyl ester (88 mg,

0.24 mmol), methanol (10 mL), water (0.5 mL), and

lithium hydroxide monohydrate (100 mg, 2.38 mmol)

was stirred for 26 h and was then partitioned between

CHCl₃/1 M HCl. The organic layer was dried over

Na₂SO₄, ﬁltered, and concentrated to aﬀord 40 (82 mg,

96%). ¹³C NMR d 172.92 (C), 134.87 (CH), 124.73

(CH), 78.53 (CH), 76.01 (CH), 66.54 (CH₂), 66.21 (CH₂),

52.67 (CH), 44.23 (CH), 43.41 (CH), 33.92 (CH₂), 33.56

(CH₂), 31.07 (CH₂), 29.33 (CH₂), 29.19 (CH₂), 28.97

(CH₂), 27.93 (CH₂), 26.52 (CH₂), 26.33 (CH₂), 26.18

(CH₂). LRMS, m/z at 377 for [(M+Na)⁺].

(5Z)-(11R,15R)-15-cyclohexyl-11,15-dihydroxy-3-oxa-

16,17,18,19,20-pentanor-5-prostenoic acid (40). To a

0 ^ꢀC solution of alcohol 10 (400 mg, 0.69 mmol) in pyri-

dine (4.0 mL) was added methanesulfonyl chloride

(150 mg, 1.4 mmol). After 15 min at 0 ^ꢀC, the reaction

was warmed to room temperature and was stirred for

4 h. The mixture was then partitioned between ethyl

acetate and saturated CuSO₄, and the organic layer was

dried over MgSO₄, ﬁltered, and concentrated to the

crude 9a mesylate (480 mg crude).

(5Z)-(11R,15R)-15-cyclohexyl-11,15-dihydroxy-3-oxa-

16,17,18,19,20-pentanor-5-prostenoic acid isopropyl ester

(47). A solution of acid 40 (60 mg, 0.17 mmol) in ace-

tone (6 mL) was treated with DBU (0.15 mL, 1.0 mmol).

After 30 min, isopropyl iodide (0.10 mL, 0.84 mmol) was

added and the reaction was stirred for 48 h. The mixture

was concentrated and the residue was puriﬁed by chro-

matography on silica gel eluting with 30–50% ethyl

acetate in hexane gradient to aﬀord 47 (40 mg, 59%; R_f

The crude mesylate was dissolved in THF (2.0 mL) at

0 ^ꢀC and a 1 M solution of LiEt₃BH (2.7 mL, 2.7 mmol)

was added. The reaction was stirred for 15 min at 0 ^ꢀC

and at room temperature for 18 h. The mixture was

added to water (20 mL) and was extracted with ethyl

acetate (3ꢂ20 mL), dried (MgSO₄), ﬁltered, and con-

centrated. The residue was puriﬁed by chromatography

on silica gel eluting with a 30–50% ethyl acetate in hex-

ane gradient to aﬀord (5Z)-(11R,15R)-11,15-bis(te-

trahydropyran-2-yloxy)-15-cyclohexyl-3-oxa-16,17,18,

19,20-pentanor-5-prostenol (337 mg, 94%; R_f0.4, 1:1

ethyl acetate/hexane).

1

0.25, 1:1 ethyl acetate/hexane). H NMR d 5.73–5.55

(m, 2H), 5.11 (septet, J=6 Hz, 1H), 4.30–4.12 (m, 2H),

4.04 (app d, J=2 Hz, 2H), 3.92 (br s, 1H), 3.38 (br s,

1H), 2.41–2.26 (m, 1H), 2.17–1.99 (m, 1H), 1.92–1.38

(m, 19H), 1.27 (d, J=6 Hz, 6H), 1.22–0.93 (m, 4H); ¹³C

NMR d 170.16 (C), 133.67 (CH), 125.52 (CH), 78.92

(CH), 75.95 (CH), 68.57 (CH), 67.45 (CH₂), 66.79

(CH₂), 53.27 (CH), 44.60 (CH), 43.59 (CH), 34.15

(CH₂), 33.38 (CH₂), 31.91 (CH₂), 29.58 (CH₂), 29.18

(CH₂), 27.94 (CH₂), 26.52 (CH₂), 26.31 (CH₂), 26.16

(CH₂), 21.80 (CH₃). LRMS, m/z at 418 for [(M+Na)⁺].

A solution of above alcohol (337 mg, 0.64 mmol), DMF

(10 mL), and PDC (1.4 g, 3.84 mmol) was stirred for 40 h,

at which time the mixture was poured into 1:1 water/

saturated KH₂PO₄(100 mL). The solution was extracted

with ethyl acetate (5ꢂ50 mL) and the combined organic

layers were washed with water (2ꢂ25 mL) and saturated

NaCl (25 mL), dried (Na₂SO₄), ﬁltered, and con-

centrated. The residue was dissolved in CHCl₃and was

treated with exess ethereal CH₂N₂until a yellow color

persisted, at which time solvent and excess CH₂N₂were

removed by an N₂stream. The residue was puriﬁed by

chromatography on silica gel eluting with a 10–30% ethyl

acetate in hexane gradient to aﬀord (5Z)-(11R,15R)-11,15

- Bis(tetrahydropyran - 2 - yloxy) - 15 - cyclohexyl - 3 - oxa-

16,17,18,19,20-pentanor-5-prostenoic acid methyl ester

(140 mg, 40%; R_f0.7, 1:1 ethyl acetate/hexane).

(5E,13E)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-

dihydroxy-3-oxa-16,17,18,19,20-pentanor-5,13-prostadie-

noic acid tert-butyl ester (44). To a solution of lactone 3

(5.7 g, 12.7 mmol) in THF (40 mL) at À78 ^ꢀC was added

dropwise a 1.5 M solution of DIBAL-H in toluene

(11.5 mL, 17.2 mmol). After 2 h, the reaction was

poured into saturated sodium potassium tartrate tetra-

hydrate (70 mL) and was stirred for 30 min to break the

emulsion. The mixture was extracted with ethyl acetate

(3ꢂ50 mL) and the combined organic layers were dried

(MgSO₄), ﬁltered, and concentrated, and the residue was

puriﬁed by chromatography on silica gel eluting with 1:1

ethyl acetate/hexane to aﬀord [3aR,4R(1E,3S),5R,6aS]-4

-[3-cyclohexyl-3-(tetrahydropyran-2-yloxy)propenyl]-5-

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2045

(tetrahydropyran-2-yloxy)-hexahydro-2H-cyclopenat[b]

furan-2-ol (27; 4.7 g, 82%).

(2ꢂ40 mL). The combined organic layers were dried

(MgSO₄), ﬁltered, and concentrated, and the residue

was puriﬁed by chromatography on silica gel eluting

with 1:1 hexane:ethyl acetate to aﬀord 9a alcohol

(5E,13E) - (9S,11R,15S) - 11,15 - bis(tetrahydropyran - 2 -

yloxy)-15-cyclohexyl-9-hydroxy-3-oxa-16,17,18,19,20-

pentanor-5,13-prostadienoic acid tert-butyl ester

(450 mg, 38%).

A mixture of 27 (5.1 g, 11.3 mmol), Ph₃P¼CHCO₂CH₃

(6.6 g, 19.7 mmol), CH₂Cl₂(50 mL), and glacial acetic

acid (8 drops) were stirred overnight. The reaction was

concentrated and the residue was puriﬁed by chroma-

tography on a silica gel column eluting with 1:1 hexane/

ethyl acetate to aﬀord the trans crotonate (5E,13E)-

(9S,11R,15S)-11,15-bis(tetrahydropyran-2-yloxy)-15-

cyclohexyl-9-hydroxy-2,3,4,16,17,18,19,20-octanor-5,

13-prostadienoic acid methyl ester (28; 5.7 g, 99%).

A solution of the above 9a alcohol (430 mg, 0.72 mmol),

PPh₃(350 mg, 1.34 mmol), and pyridine (112 mg,

1.42 mmol) in CH₃CN (6 mL) was treated with CCl₄

(240 mg, 1.55 mmol). After stirring overnight the reac-

tion was concentrated and the residue was puriﬁed by

chromatography on silica gel to aﬀord a mixture of the

9b choride (5E,13E)-(9R,11R,15S)-11,15-bis(tetrahy-

dropyran-2-yloxy)-9-chloro-15-cyclohexyl-3-oxa-16,17,

18,19,20-pentanor-5,13-prostadienoic acid tert-butyl

ester and the 9-deschloro-Á^5,6,8,9diene by-product (for-

mally derived by HCl elimination) (5E,13E)-(11R,15S)-

11,15-bis(tetrahydropyran-2-yloxy)-15-cyclohexyl-3-oxa-

A mixture of 28 (5.7 g, 11.8 mmol), CH₂Cl₂(150 mL),

imidazole (1.46 g, 21.5 mmol), DMAP (500 mg,

4.1 mmol), and Me₂Bu^tSiCl (2.54 g, 16.9 mmol) was

stirred for 1 h. Saturated NH₄Cl (50 mL) was added, the

phases were separated, the aqueous layer was extracted

with CH₂Cl₂(2ꢂ50 mL), and the combined organic

layers were dried (MgSO₄), ﬁltered, and concentrated.

The residue was puriﬁed by chromatography on silica

gel eluting with 20% ethyl acetate in hexane to provide

the 9a silyl ether (5E,13E)-(9S,11R,15S)-11,15-bis(te-

trahydropyran-2-yloxy)-9-(t-butyldimethylsiloxy)-15-

cyclohexyl - 2,3,4,16,17,18,19,20 - octanor - 5,13 - prosta-

dienoic acid methyl ester (6.05 g, 84%).

16,17,18,19,20-pentanor-5,13,8(9)-prostatrienoic acid

tert-butyl ester (362 mg, 82% calculated as the chloride).

A solution of the above compound mixture (310 mg,

0.51 mmol calculated as the chloride), THF (5 mL),

water (1 mL), and acetic acid (9 mL) was heated at 65 ^ꢀC

for 1 h. The solution was concentrated and the residue

was puriﬁed by chromatography on silica gel eltuing

with 4:1 ethyl acetate:hexane to aﬀord a mixture of 44

and the corresponding Á^5,6,8,9diene side product

(188 mg, 83% calculated as the chloride). This mixture

was puriﬁed by reverse-phase HPLC to aﬀord pure 44

(58 mg, 26% from the 9a alcohol). ¹³C NMR d 169.67

(C), 134.67 (CH), 133.09 (CH), 131.18 (CH), 128.56

(CH), 81.62 (C), 77.31 (CH), 75.04 (CH), 71.63 (CH₂),

67.59 (CH₂), 59.38 (CH), 56.34 (CH), 53.08 (CH), 43.38

(CH₂), 43.32 (CH), 33.88 (CH₂), 28.87 (CH₂), 28.77

(CH₂), 28.10 (CH₃), 26.48 (CH₂), 26.05 (CH₂), 25.97

(CH₂). HRMS, m/z calcd for C₂₄H₄₀O₅Cl [(M+H)⁺],

445.2535; found, 445.2574.

To a solution of the above silyl ether (6.0 g, 9.8 mmol) in

THF (50 mL) at 0 ^ꢀC was added dropwise a 1.5 M solu-

tion of DIBAL-H in toluene (16 mL, 24 mmol). The

reaction was brought to room temperature and was

stirred for 2 h, at which time saturated sodium potas-

sium tartrate tetrahydrate (75 mL) was added. The

mixture was stirred for 25 min to break the emulsion,

the layers were separated, and the aqueous phase was

extracted with ethyl acetate (2ꢂ50 mL). The combined

organic layers were dried (MgSO₄), ﬁltered, and con-

centrated, and the residue was puriﬁed by chromato-

graphy on silica gel eluting with 25% ethyl acetate in

hexane to yield the alcohol reduction product (5E,13E)-

(9S,11R,15S)-11,15-bis(tetrahydropyran-2-yloxy)-9-(t-

butyldimethylsiloxy)-15-cyclohexyl-2,3,4,16,17,18,19,20-

octanor-5,13-prostadienol (4.28 g, 74%).

(5E,13E)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-

dihydroxy-3-oxa-16,17,18,19,20-pentanor-5,13-prostadi-

enoic acid (26). A solution of 44 (22 mg, 0.050 mmol),

water (1 mL), methanol (2 mL), and lithium hydroxide

monohydrate (17 mg, 0.41 mmol) was stirred for 20 h.

Saturated citric acid (10 mL) was added and the solu-

tion was extracted with CHCl₃(3ꢂ10 mL), dried

(Na₂SO₄), ﬁltered, and concentrated to aﬀord 26

(19 mg, 98%). ¹³C NMR d 173.22 (C), 134.60 (CH),

132.94 (CH), 131.66 (CH), 128.44 (CH), 77.79 (CH),

75.24 (CH), 71.99 (CH₂), 66.59 (CH₂), 58.93 (CH),

55.42 (CH), 52.80 (CH), 43.29 (CH₂), 43.18 (CH), 32.77

(CH₂), 28.89 (CH₂), 28.83 (CH₂), 26.46 (CH₂), 26.00

(CH₂), 25.92 (CH₂). LRMS, m/z calcd for C₂₀H₃₁O₅Cl

(M⁺), 386.1860; found, 386.1859.

A mixture of the above alcohol (2.4 g, 4.1 mmol), water

(25 mL), toluene (30 mL), NaOH (3.8 g, 95 mmol),

Bu₄NHSO₄(300 mg, 0.88 mmol), and BrCH₂CO₂Bu^t

(5.0 g, 26 mmol) was vigorously stirred overnight. The

layers were separated, the aqueous phase was extracted

with ethyl acetate (2ꢂ50 mL), and the combined organic

layers were dried (MgSO₄), ﬁltered, and concentrated.

The residue was puriﬁed by chromatography on silica

gel eluting with 20% ethyl acetate in hexane to aﬀord

the O-alkylated product (5E,13E)-(9S,11R,15S)-11,15-

bis(tetrahydropyran-2-yloxy)-9-(t-butyldimethylsiloxy)-

15-cyclohexyl-3-oxa-16,17,18,19,20-pentanor-5,13-pros-

tadienoic acid tert-butyl ester (1.48 g, 48%).

A solution of the above compound (1.4 g, 2.0 mmol) in

THF (20 mL) was treated with a 1 M solution of TBAF

in THF (6 mL, 6 mmol). After 2 h, saturated NH₄Cl

(30 mL) was added, the phases were separated, and the

aqueous layer was extracted with ethyl acetate

(5Z)-(9R,11R,15S)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

isopropyl ester (29). Beginning with the 15b alcohol

30,⁶the title compound was synthesized analogously to

its 15R diastereomer AL–6598 in 13 steps and 1.7%

2046

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

yield. ¹³C NMR d 170.21 (C), 131.12 (CH), 127.19

(CH), 76.75 (CH), 75.44 (CH), 68.70 (CH), 67.67 (CH₂),

66.78 (CH₂), 61.02 (CH), 54.28 (CH), 51.18 (CH), 44.31

(CH), 44.19 (CH), 31.35 (CH₂), 31.19 (CH₂), 29.73

(CH₂), 27.60 (CH₂), 26.50 (CH₂), 26.31 (CH₂), 26.16

(CH₂), 21.80 (CH₃). CI LRMS, m/z calcd For

C₂₃H₄₀O₅Cl [(M+H)⁺], 431; found, 431.

gel eluting with 20% ethyl acetate in hexane to aﬀord

the 11-siloxy derivative (5Z)-(9R,11R,15R)-11-(t-butyl-

dimethylsiloxy)-9-chloro-15-cyclohexyl-15-hydroxy-3-

oxa-16,17,18,19,20-pentanor-5-prostenoic acid tert-

butyl ester (87 mg, 55%).

The silyl ether from above (80 mg, 0.14 mmol), 2,6-di-t-

butylpyridine (100 mg, 0.52 mmol), CH₂Cl₂(2 mL), and

methyl triﬂuoromethanesulfonate (80 mg, 0.51 mmol)

was reﬂuxed for 24 h. After cooling to room tempera-

ture the solution was added to saturated NaHCO₃

(10 mL), extracted with CH₂Cl₂(3ꢂ10 mL), dried

(MgSO₄), ﬁltered, and concentrated. The residue was

puriﬁed by chromatography on silica gel eluting with

10% ethyl acetate in hexane to aﬀord the 11-siloxy, 15-

methoxy compound (5Z)-(9R,11R,15R)-11-(t-butyldi-

methylsiloxy)-9-chloro-15-cyclohexyl-15-methoxy-3-oxa-

16,17,18,19,20-pentanor-5-prostenoic acid tert-butyl

ester (35 mg, 44%).

(5Z)-(9R,11R,15S)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

(38). A mixture of 29 (52 mg, 0.12 mmol), lithium

hydroxide monohydrate (35 mg, 0.83 mmol), methanol

(9 mL), and water (2 mL) was stirred for 24 h. A 1 M

solution of HCl (2 mL) was added and the solution was

extracted with CH₂Cl₂(3ꢂ20 mL), dried (Na₂SO₄), ﬁl-

tered, and concentrated to aﬀord 38 (33 mg, 71%). ¹³C

NMR d 166.64 (C), 132.11 (CH), 126.56 (CH), 77.14

(CH), 75.63 (CH), 66.53 (CH₂), 61.02 (CH), 54.38 (CH),

51.16 (CH), 44.18 (CH), 44.10 (CH), 31.44 (CH₂), 31.27

(CH₂), 29.99 (CH₂), 29.13 (CH₂), 27.57 (CH₂), 26.47

(CH₂), 26.29 (CH₂), 26.14 (CH₂). HRMS, m/z calcd for

C₂₀H₃₄O₅Cl [(M+H)⁺], 389.2095; found, 389.2089.

The above compound (32 mg, 0.056 mmol) was dis-

solved in THF (1.5 mL) and TBAF (0.12 mL of a 1 M

solution in THF, 0.12 mmol) was added. After 30 min

saturated NH₄Cl (4 mL) was added, the mixture was

extracted with ethyl acetate (3ꢂ5 mL), dried (MgSO₄),

ﬁltered, and concentrated. The residue was puriﬁed by

chromatography on silica gel eluting with 40% ethyl

acetate in hexane to aﬀord 49 (24 mg, 94%). ¹³C NMR

d 169.77 (C), 130.90 (CH), 127.43 (CH), 85.89 (CH),

81.69 (C), 76.05 (CH), 67.83 (CH₂), 66.56 (CH₂), 61.00

(CH₂), 57.83 (CH₃), 54.06 (CH), 51.92 (CH), 44.45

(CH₂), 40.65 (CH), 29.92 (CH₂), 29.83 (CH₂), 29.02

(CH₂), 28.42 (CH₃), 28.10 (CH₂), 26.64 (CH₂), 26.37

(CH₂). HRMS, m/z calcd for C₂₅H₄₄O₅Cl [(M+H)⁺],

459.2877; found, 459.2878.

(5Z,13E)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-

dihydroxy-3-oxa-16,17,18,19,20-pentanor-5,13-prostadi-

enoic acid isopropyl ester (46). Starting with the 15R

diol 30,⁶the title compound was synthesized analo-

gously to AL–6598 in 12 steps and 0.88% yield. ¹³C

NMR d 170.14 (C), 134.71 (CH), 131.60 (CH), 130.56

(CH), 127.41 (CH), 76.95 (CH), 75.44 (CH), 68.66

(CH), 67.57 (CH₂), 66.66 (CH₂), 59.63 (CH), 55.81

(CH), 53.42 (CH), 43.76 (CH₂), 43.64 (CH), 28.92

(CH₂), 28.67 (CH₂), 28.58 (CH₂), 26.51 (CH₂), 26.13

(CH₂), 26.05 (CH₂), 21.82 (CH₃). HRMS, m/z calcd for

C₂₃H₃₈O₅Cl [(M+H)⁺], 427.2251; found, 427.2249.

(5Z,13E)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-

dihydroxy-3-oxa-16,17,18,19,20-pentanor-5,13-prostadi-

enoic acid (36). A solution of 46 (30 mg, 0.070 mmol),

lithium hydroxide monohydrate (25 mg, 0.71 mmol),

methanol (1 mL), and water (0.3 mL) was stirred for

22 h. Saturated KH₂PO₄(6 mL) was added and the

mixture was extracted with ethyl acetate (3ꢂ4 mL),

dried (Na₂SO₄), ﬁltered, and concentrated to aﬀord 36

(20 mg, 74%). ¹³C NMR d 173.22 (C), 134.11 (CH),

132.44 (CH), 131.90 (CH), 126.37 (CH), 77.52 (CH),

75.20 (CH), 66.50 (CH₂), 66.03 (CH₂), 59.60 (CH),

56.34 (CH), 53.74 (CH), 43.93 (CH₂), 43.33 (CH), 29.09

(CH₂), 28.82 (CH₂), 28.63 (CH₂), 26.42 (CH₂), 26.05

(CH₂), 25.96 (CH₂). HRMS, m/z calcd for C₂₀H₃₂O₅Cl

[(M+H)⁺], 387.1938; found, 387.1911.

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11-hydroxy-

15-methoxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic

acid (31). A solution of 49 (12 mg, 0.026 mmol), lithium

hydroxide monohydrate (10 mg, 0.24 mmol), methanol

(4 mL), and water (0.5 mL) was stirred for 24 h. Satu-

rated citric acid (5 mL) was added and the mixture was

extracted with CH₂Cl₂(4ꢂ5 mL), dried (Na₂SO₄), ﬁl-

tered, and concentrated to aﬀord 31 (7.0 mg, 67%). ¹³C

NMR d 172.46 (C), 132.26 (CH), 126.34 (CH), 86.21

(CH), 75.86 (CH), 66.64 (CH₂), 66.31 (CH₂), 61.07

(CH), 57.77 (CH₃), 53.77 (CH), 51.95 (CH), 44.36

(CH₂), 40.62 (CH), 30.44 (CH₂), 29.32 (CH₂), 29.02

(CH₂), 28.42 (CH₂), 27.97 (CH₂), 26.60 (CH₂), 26.33

(CH₂). HRMS, m/z calcd for C₂₁H₃₆O₅Cl [(M+H)⁺],

403.2251; found, 403.2261.

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11-hydroxy-

15-methoxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic

acid tert-butyl ester (49). To a solution of 32 (127 mg,

0.285 mmol, prepared analogously to its corresponding

(5Z,13E)-(9R,11R,15S)-9-Chloro-15-cyclohexyl-11,15-di-

hydroxy-3-oxa-16,17,18,19,20-pentanor-5,13-prostadie-

nol (37). To a solution of 43 (41 mg, 0.093 mmol) in

THF (5 mL) at 0 ^ꢀC was added a 1.5 M solution of

DIBAL-H in toluene (0.7 mL, 1.05 mmol). After warm-

ing to room temperature and stirring for an additional

1.5 h, saturated NH₄Cl (15 mL) was added. The mixture

was extracted with ethyl acetate (3ꢂ15 mL), dried

(MgSO₄), ﬁltered, and concentrated, and the residue

was puriﬁed by chromatography on silica gel eluting

with ethyl acetate to aﬀord 37 (21 mg, 68%). ¹³C NMR

isopropyl

ester

AL–6598),

imidazole

(49 mg,

0.72 mmol), DMAP (10 mg, 0.082 mmol), and CH₂Cl₂

(5 mL) was added t-butyldimethylsilyl chloride (90 mg,

0.59 mmol). After 24 h saturated NH₄Cl (10 mL) was

added and the mixture was extracted with CH₂Cl₂

(3ꢂ10 mL), dried (MgSO₄), ﬁltered, and concentrated.

The residue was puriﬁed by chromatography on silica

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

2047

d 134.59 (CH), 133.00 (CH), 129.61 (CH), 128.21 (CH),

128.21 (CH), 77.56 (CH), 75.16 (CH), 71.54 (CH₂), 67.93

(CH₂), 66.46 (CH₂), 61.76 (CH), 59.49 (CH), 55.85 (CH),

53.23 (CH), 43.43 (CH), 28.81 (CH₂), 28.56 (CH₂),

26.46 (CH₂), 26.94 (CH₂), 26.02 (CH₂), 25.57 (CH₂).

HRMS, m/z calcd for C₂₀H₃₄O₄Cl [(M+H⁺], 373.2146;

found, 373.2101.

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

n-butyl amide (34). A solution of Me₃Al (2 M in tolu-

ene, 0.58 mL, 1.6 mmol) was added to n-BuNH₂(90 mg,

1.2 mmol) in toluene (1.5 mL). After 25 min a solution

of AL–6598 (106 mg, 0.246 mmol) in toluene (1.5 mL)

was added. After 3 h the reaction was quenched by the

addition of saturated KH₂PO₄(3 mL). The mixture was

extracted with ethyl acetate (2ꢂ4 mL) and the combined

organic layers were dried (Na₂SO₄), decanted, and con-

centrated. The residue was puriﬁed by chromatography

on silica gel eluting with ethyl acetate to aﬀord 34

(56 mg, 51% yield). ¹³C NMR d 169.70 (C), 131.36

(CH), 126.88 (CH), 76.02 (CH), 75.70 (CH), 69.41 (CH₂),

566.75 (CH₂), 60.73 (CH), 54.12 (CH), 51.57 (CH), 44.66

(CH₂), 43.62 (CH), 38.72 (CH₂), 31.72 (CH₂), 29.80

(CH₂), 29.37 (CH₂), 29.32 (CH₂), 28.20 (CH₂), 26.58

(CH₂), 26.38 (CH₂), 26.23 (CH₂), 20.16 (CH₂), 13.84

(CH₃). HRMS, m/z calcd for C₂₄H₄₃O₄NCl [(M+H)⁺],

444.287856; found, 444.28784.

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenol (42). A

solution of (5Z)-(9R,11R,15R)-11,15-bis(tetrahydropyran-

2-yloxy)-9-chloro-15-cyclohexyl-3-oxa-16,17,18,19,20-

pentanor-5-prostenoic acid tert-butyl ester (the

C11,C15-bisTHP ether of 32, 150 mg, 0.24 mmol) in

THF (5.0 mL) was cooled to 0 ^ꢀC and DIBAL-H

(0.5 mL of a 1.5 M solution in toluene, 0.75 mmol) was

added. After 2.5 h, saturated sodium potassium tartrate

(10 mL) was added and the mixture was stirred at room

temperature for 1 h to break the emulsion. The organic

layer was separated and the aqueous phase was extrac-

ted with ethyl acetate (5ꢂ10 mL). The combined organic

layers were dried (MgSO₄), ﬁltered, and concentrated,

and the residue was puriﬁed by chromatography on

silica gel eluting with 30% ethyl acetate in hexane to

aﬀord the alcohol (5Z)-(9R,11R,15R)-11,15-bis(tetrahy-

dropyran-2-yloxy)-9-chloro-15-cyclohexyl-3-oxa-16,17,

18,19,20-pentanor-5-prostenol (114 mg, 87%; R_f=0.15,

30% ethyl acetate in hexane).

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

dimethyl amide (35). To a solution of 32 (101 mg,

0.22 mmol) in toluene (5 mL) was added 2 mL of a stock

solution prepared by the addition of Me₃Al (2 M in

toluene, 2 mL, 4 mmol) to a toluene (3 mL) solution of

Me₂NH₂Cl (430 mg, 5.3 mmol). The reaction was

heated at 60 ^ꢀC for 27 h and was then cooled to room

temperature. Toluene (50 mL) and saturated sodium

potassium tartrate were added and the mixture was

stirred for 1 h. The layers were separated, the aqueous

phase was extracted with ethyl acetate (3ꢂ10 mL), and

the combined organic layers were washed with saturated

NaCl (3ꢂ10 mL). The organic layer was dried

(Na₂SO₄), ﬁltered, and concentrated, and the residue

was puriﬁed by chromatography on Florisil eluting ﬁrst

with ethyl acetate and then with acetone to aﬀord 35

(20 mg, 22%; R_f0.12, ethyl acetate). ¹³C NMR d 169.25

(C), 132.38 (CH), 126.54 (CH), 75.45 (CH), 74.48 (CH),

68.47 (CH₂), 66.58 (CH₂), 62.00 (CH), 54.39 (CH),

50.50 (CH), 44.36 (CH₂), 43.62 (CH), 36.12 (CH₃), 35.55

(CH₃), 31.31 (CH₂), 30.89 (CH₂), 30.29 (CH₂), 29.40

(CH₂), 28.01 (CH₂), 26.57 (CH₂), 26.33 (CH₂), 26.17

(CH₂). HRMS, m/z calcd for C₂₂H₃₉NO₄Cl [(M+H)⁺],

416.2568; found, 416.2560.

The above alcohol (54 mg, 0.09 mmol) was heated at

70 ^ꢀC for 1 h in 65% aqueous acetic acid. The mixture

was concentrated and the residue was puriﬁed by chro-

matography on silica gel eluting with ethyl acetate to

1

aﬀord 42 (33 mg, 88% yield; R_f0.15, ethyl acetate). H

NMR d 5.68 (m, 2H), 4.08 (m, 4H), 3.74 (m, 2H), 3.42

(m, 1H), 2.37 (m, 2H), 2.35–1.90 (m, 4H), 1.85–0.90

(broad m, 18H). ¹³C NMR d 131.06 (CH), 127.52 (CH),

75.80 (CH), 75.54 (CH), 71.94 (CH₂), 66.38 (CH₂),

66.38 (CH₂), 61.82 (CH₂), 60.82 (CH₂), 54.05 (CH),

50.87 (CH), 44.69 (CH), 43.60 (CH), 31.29 (CH₂), 29.71

(CH₂), 29.46 (CH₂), 29.22 (CH₂), 28.08 (CH₂), 26.48

(CH₂), 26.28 (CH₂), 26.14 (CH₂). HRMS, m/z calcd for

C₂₀H₃₆O₄Cl [(M+H)⁺], 375.2302; found, 375.2299.

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

amide (33). A mixture of 32 (42 mg, 0.09 mmol), NH₄Cl

(130 mg, 2.4 mmol), and liquid NH₃(2 mL) were heated

in a sealed pressure tube to 70 ^ꢀC. After 24 h the reac-

tion was cooled to À78 ^ꢀC, the vessel was opened, and

the mixture was warmed to room temperature to eva-

porate the NH₃. The residue was dissolved in ethyl ace-

tate, ﬁltered, and concentrated, and the residue was

puriﬁed by chromatography on Florisil eluting with a

gradient of 50% ethyl acetate in hexane to 40% hexane

in acetone to aﬀord 33 (20 mg, 57%; R_f0.13, 50% hex-

ane in acetone). ¹³C NMR d 172.72 (C), 131.47 (CH),

126.81 (CH), 75.92 (CH), 75.68 (CH), 69.23 (CH₂),

66.71 (CH₂), 60.61 (CH), 54.03 (CH), 51.44 (CH), 44.65

(CH₂), 44.61 (CH₂),43.55 (CH), 31.55 (CH₂), 29.74

(CH₂), 29.34 (CH₂), 29.24 (CH₂), 28.04 (CH₂), 26.46

(CH₂), 26.27 (CH₂), 26.12 (CH₂). HRMS, m/z calcd for

C₂₀H₃₅NO₄Cl [(M+H)⁺], 388.2255; found, 388.2252.

(5Z)-(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihy-

droxy-3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid

N-methyl amide (41). To

a

solution of (5Z)-

(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihydroxy-

3-oxa-16,17,18,19,20-pentanor-5-prostenoic acid methyl

ester (125 mg, 0.311 mmol; prepared in quantitative

yield by treatment of the acid AL-6556 with diazo-

methane) in toluene (5 mL) was added a stock solution

(2.8 mL) prepared by the addition of 2 M Me₃Al

(2.0 mL, 4.0 mmol) to a toluene (3 mL) suspension of

MeNH₃Cl (360 mg, 5.3 mmol). After stirring for 30 min

the mixture was heated to 50 ^ꢀC (bath temperature)

overnight. The mixture was cooled to room temperature

and diluted with toluene (50 mL) and then stirred with

saturated sodium potassium tartrate for 1 h. The layers

were separated, the aqueous phase was extracted with

2048

M. R. Hellberg et al. / Bioorg. Med. Chem. 10 (2002) 2031–2049

ethyl acetate, and the combined organic layes were dried

over MgSO₄, ﬁltered, and concentrated. The residue

was puriﬁed by chromatography on a 15 cm tallꢂ20 mm

diameter silica gel column using 1:1 ethyl acetate/hex-

ane!ethyl acetate!20% acetone in ethyl acetate gra-

dient elution to aﬀord 41 (98 mg, 78%). ¹³C NMR d

170.48 (C), 131.42 (CH), 126.87 (CH), 75.92 (CH), 75.61

(CH), 69.35 (CH₂), 66.68 (CH₂), 60.64 (CH), 53.99

(CH), 51.43 (CH), 44.56 (CH₂), 43.52 (CH), 31.57

(CH₂), 29.69 (CH₂), 29.28 (CH₂), 29.22 (CH₂), 28.08

(CH₂), 26.47 (CH₂), 26.27 (CH₂), 26.12 (CH₂), 25.56

(CH₃). HRMS, m/z calcd for C₂₁H₃₇NO₄Cl [(M+H)⁺],

402.2411; found, 402.2413.

monkeys (Macaca fascicularis) that had previously had

permanent ocular hypertension induced in the right eye

by laser trabeculoplasty. All left eyes were normal and

normotensive. The animals were trained to sit in

restraint ‘chairs’ (designed for glaucoma studies) and

conditioned to accept dosing and pressure measure-

ments without chemical restraint. In the monkey IOP

model the compound was instilled (1ꢂ30 uL) twice a

day for a total of ﬁve doses. IOP was recorded 2, 4, and

6 h after the ﬁrst dose, 16 h after the fourth dose, and 2,

4, and 6 h after the ﬁfth dose. The reduction in IOP is

reported as percent change from baseline measurements

made prior to the initial dose. Compounds were gen-

erally formulated in a tromethamine/boric acid buﬀer

containing 1.5% cremophor EL, 0.1% EDTA, and

0.01% benzalkonium chloride, pH 7.4.

(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihydroxy-

3-oxa-16,17,18,19,20-pentanorprostanoic acid t-butyl es-

ter (48). A solution of 32 (23 mg, 0.052 mmol) in ethyl

acetate (5 mL) containing 5% Rh/Al₂O₃(8 mg) was

stirred under 1 atmosphere pressure of H₂. The mixture

was ﬁlterred through a pad of Celite and concentrated,

and the residue was puriﬁed by chromatography on a

on a 15 cm tallꢂ10 mm diameter silica gel column elut-

ing with a gradient of 30–60% ethyl acetate in hexane to

provide 48 (18 mg, 77%). ¹³C NMR 169.87 (C), 81.54

(C), 76.18 (CH), 71.40 (CH₂), 68.71 (CH₂), 61.85 (CH),

54.27 (CH), 52.69 (CH), 44.72 (CH₂), 43.65 (CH), 33.19

(CH₂), 31.74 (CH₂), 30.33 (CH₂), 29.80 (CH₂), 29.25

(CH₂), 28.11 (CH₃), 27.94 (CH₂), 26.48 (CH₂), 26.28

(CH₂), 26.12 (CH₂), 23.48 (CH₂). HRMS, m/z calcd for

C₂₄H₄₄O₅Cl [(M+H)⁺], 447.2877; found, 447.2872.

References and Notes

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2. Sugrue, M. F. J. Med. Chem. 1997, 40, 2793.

3. (a) Bito, L. Z. Surv. Ophthalmol. 1997, 41 (Suppl. 2), S1. (b)

Alm, A. Prog. Retin. Eye Res. 1998, 17, 291. (c) Linden, C.;

Alm, A. Drugs Aging 1999, 14, 387.

4. Goh, Y.; Nakajima, M.; Azuma, I.; Hayaishi, O. Jpn. J.

Ophthalmol. 1988, 32, 471.

5. (a) Goh, Y.; Nakajima, M.; Azuma, I. Brit. J. Ophthalmol.

1988, 72, 461. (b) Woodward, D. F.; Spada, C. S.; Hawley,

S. B.; Williams, L. S.; Protzman, C. E.; Nieves, A. L. Eur. J.

Pharmacol. 1993, 230, 327. (c) Matsugi, T.; Kageyama, M.;

Nishimura, K.; Giles, H.; Shirasawa, E. Eur. J. Pharmacol.

1995, 275, 245. (d) Woodward, D. F.; Hawley, S. B.; Williams,

L. S.; Ralston, T. R.; Protzman, C. E.; Spada, C. S.; Nieves,

A. L. Invest. Ophthamol. Vis. Sci. 1990, 31, 138. (e) Nakajima,

M.; Goh, Y.; Azuma, I.; Hayashi, O. Graefe’s Arch. Clin. Exp.

(9R,11R,15R)-9-Chloro-15-cyclohexyl-11,15-dihydroxy-

3-oxa-16,17,18,19,20-pentanorprostanoic acid (39). A

.

solution of 48 (7 mg, 0.02 mmol), LiOH H₂O (5 mg,

0.12 mmol), methanol (0.5 mL), and water (0.2 mL) was

stirred for 19 h. The mixture was partitioned between

CHCl₃(20 mL)/0.1 M HCl (10 mL). The phases were

separated and the aqueous layer was extracted with

CHCl₃(2ꢂ10 mL). The combined organic layers were

dried (Na₂SO₄), ﬁltered, and concentrated to aﬀord 39

(7 mg, 100%). ¹³C NMR d 172.89 (C), 76.42 (CH), 75.96

(CH), 71.35 (CH₂), 67.91 (CH₂), 61.68 (CH), 53.94

(CH), 52.29 (CH), 44.74 (CH₂), 43.36 (CH), 32.47 (CH₂),

31.20 (CH₂), 29.53 (CH₂), 29.45 (CH₂), 29.19 (CH₂),

27.99 (CH₂), 26.44 (CH₂), 26.25 (CH₂), 26.09 (CH₂),

23.21(CH₂). HRMS, m/z calcd for C₂₀H₃₆O₅Cl

[(M+H)⁺], 391.2251; found, 391.2214.

Ophthamol. 1991, 229, 411. (f) Thierauch, K.-H.; Sturzebecher,

¨

W.; Vorbruggen, H.; Prostaglandins 1988, 35, 855. (g) Schulz,

¨

C. St.; Schillinger, E.; Rehwinkel, H.; Raduchel, B.; Skuballa,

¨

B. G.; Beckman, R.; Muller, B.; Schroder, G.; Maass, B.;

Thierauch, K.-H.; Buchmann, B.; Verhallen, P. F. J.; Froh-

lich, W. Adv. Prostaglandin Thromboxane Leukotriene Res.

1991, 21, 21 B591. (h) Taisho Pharmaceutical Co. has dis-

closed the IOP lowering eﬀect of several 9b-chloro-3-thia-15-

cyclohexyl-13,14-alkynyl analogues of PGF_1a

. Sato, F.;

Amano, T.; Kameo, K.; Tanami, T.; Mutoh, M.; Ono, N.;

Goto, J. EP 737676A1.

6. (a) Buchmann, B.; Skuballa, W.; Vorbruggen, H. Tetra-

¨

hedron Lett. 1990, 31, 3425. (b) Buchmann, B.; Skuballa, W.;

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¨

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¨

Article Doi

3-Oxa-15-cyclohexyl prostaglandin DP receptor agonists as topical antiglaucoma agents.

DOI: 10.1016/S0968-0896(02)00016-0

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Full text of DOI:10.1016/S0968-0896(02)00016-0

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