Inhibitors of biotin biosynthesis as potential herbicides

Tetrahedron 60 (2004) 1731–1748

d

Ayelet Nudelman,^aDana Marcovici-Mizrahi,^bAbraham Nudelman,^cDennis Flint

,

*

and Vernon Wittenbach^e

^aQBI Enterprises Ltd., Weizmann Science Park, Ness Ziona 70400, Israel

^bDepartment of Organic Chemistry, Israel Institute for Biological Research, PO Box 19, Ness Ziona 74100, Israel

^cDepartment of Chemistry, Bar Ilan University, Ramat Gan 52900, Israel

^dE. I. Du Pont de Nemours and Company, Central Research and Development, Experimental Station, Wilmington, DE 19880-0328, USA

^eE. I. Du Pont de Nemours and Company, Stine-Haskell Research Center, Newark, DE 19714, USA

Received 2 December 2003; accepted 18 December 2003

Abstract—Isosteric derivatives and analogues of the 7-keto-8-aminopelargonic acid (KAPA), 7,8-diaminopelargonic acid (DAPA) and

desthiobiotin (DTB) vitamer intermediates involved in the biosynthetic pathway of biotin were prepared and evaluated as potential

herbicides. The most active compound was desmethyl-KAPA which displayed a GR₅₀(concentration of the active compound that causes a

50% growth inhibition) value of 8 ppm, where values ,50 ppm are considered herbicidal. Other KAPA analogs where the terminal Me group

was replaced by bulkier substituents such as Et, i-Pr and HOCH₂showed moderate activity.

1. Introduction

biotin to metabolism is derived from its participation in

many vital metabolic processes, such as gluconeogenesis,

biosynthesis of fatty acids and metabolism of amino acids.

Perhaps its most important role is in the carboxylation of

acetyl-CoA to give malonyl-CoA, which is the ﬁrst step in

Biotin, a water soluble vitamin, functions as a coenzyme in

carboxylation and transcarboxylation reactions critical to

microorganisms, plants and animals.¹The importance of

Figure 1. Biosynthetic pathway of biotin.

Keywords: Biotin; Biotin vitamers; 7-Keto-8-aminopelerginic acid (KAPA); 7,8-Diaminopelargonic acid (DAPA); Desthiobiotin (DTB); Herbicides; Enzyme

inhibitors.

*

Corresponding author. Tel.: þ972-3-531-8314; fax: þ972-3-535-1250; e-mail address: nudelman@mail.biu.ac.il

doi:10.1016/j.tet.2003.12.047

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A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

Scheme 1. General synthesis of KAPA analogs.

fatty acid biosynthesis. Since fatty-acid synthesis is

essential for the growth and development of most organ-

isms, biotin is thus an essential nutrient for plants and

animals. Plants, microorganisms and some fungi biosynthe-

size their own biotin, while animals and man require trace

amounts of the vitamin in their diet.

synthase stems from an iron–sulfur cluster found in this

enzyme.⁵

Inhibitors of enzymes involved in the biosynthesis of

essential plant nutrients can cause irreparable damage to

plants, and for this reason such enzymes can be useful

targets for the rational design of inhibitors in the hopes of

ﬁnding new herbicides. We describe the synthesis and

biological evaluation of analogs of biotin and biotin

vitamers (molecules, such as intermediates in the biotin

biosynthetic pathway, that can be converted into biotin in

vivo) as potential enzyme inhibitors with the objective of

ﬁnding some that exhibit herbicidal activity. Moreover,

since the enzymes involved in the biotin biosynthetic

The biotin biosynthetic pathway²(Fig. 1), involving the

KAPA, DAPA and DTB vitamers, is well understood in

microorganisms³but has not been clearly elucidated in

plants. However, there is increasing evidence that plants

synthesize it by a similar route to that used by E. coli.⁴

Recent studies indicate that the source of the sulfur atom, in

the conversion of DTB to biotin, catalyzed by biotin

Scheme 2. Synthesis of KAPA analogs derived from cysteine.

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1733

Scheme 3. Synthesis of KAPA analogs derived from THP-protected serine and threonine.

pathway are absent in higher organisms, it is expected that

inhibitors of biotin biosynthesis will possess minimal

toxicity in animals and man.

compounds prepared from various amino acids, resulting in

modiﬁcations of the terminal Me group.

2.1. KAPA analogs

Substrates 1 (Scheme 1, Table 1) were derivatives of natural

L-amino acids with the exclusion of the racemic N-Boc-a-

aminobutyric acid (1c R¼Et), S-benzyl-cysteine (1k R¼

BnSCH₂) and S-Boc-cysteine (1k R¼BocSCH₂).

2. Results and discussion

Based on the structures of the vitamers of biotin, several

families of analogs were developed, each featuring one or

more isosteric modiﬁcations. The synthetic approaches to

these derivatives were based to a large extent on our earlier

synthesis of the vitamers.⁶The compounds described below

are analog derivatives of KAPA, DAPA and DTB having

chain lengths of nine carbon atoms, focusing primarily on

The syntheses of KAPA analogs derived from cysteine 4j,

serine 4p and threonine 4r, that required additional

protection of the S and O atoms, are shown in Schemes

2–4. An initial attempt to prepare 4j involved reaction of

Scheme 4. Synthesis of KAPA analogs derived from serine and threonine.

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A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

Scheme 5. Synthesis of DTB and thio-DTB derivatives.

Bn-S-cysteine (Bn) to give the desired b-ketoester analog

2m. However, due to the high nucleophilic character of the

S atom, alkylation of 2m with I–(CH₂)₅–COOEt took place

preferentially at S rather than at C (Scheme 1). Other

cysteine derivatives protected both at the S and the N with

Boc (1kI), CBZ (1lII) or Ac (1nIV)⁷groups, gave poor

yields of the respective derivatives 2. The desired 4j was

ﬁnally obtained from thiazolidine 7 that possessed a

sterically hindered sulﬁde group (Scheme 2).

(Scheme 4). In contrast to compounds of structure 2, which

were alkylated in acetone in the presence of four equivalents

of K₂CO₃, the alkylation of 16⁰p and 16⁰r readily proceeded

with one equivalent of base in 2-butanone (MEK).

2.2. DAPA and DTB analogs

The synthesis of the neighboring diamino functionality

found in the DAPA skeleton was approached via oximation

of the a-amino-keto group of the KAPA analogs 4.⁶

Although the a-amino-oximes 18a and 18b were obtained

as mixtures of syn and anti-isomers, one isomer predomi-

nated. This encouraged us to believe that the chiral center at

C-8 could induce stereoselectivity upon oximation and

would do so in the subsequent reductive step leading to

Attempted alkylation on the respective b-ketoester deriva-

tives of N-Boc-O-THP-protected serine 2⁰qI or threonine

2⁰sI led to elimination of THP-OH to give compound 10⁰I,

which was not isolated and was identiﬁed only by its

characteristic vinylic peaks in the NMR spectrum. To

prevent this base catalyzed elimination an alternative

approach to 4p and 4q involved the coupling of the

diprotected N-Boc-O-THP-serine and threonine with the

nitrile derivative 12. Although the desired cyano esters

13⁰qI and 13⁰sI were obtained, subsequent hydrolysis and

decarboxylation gave KAPA-analogs 14q and 14s where the

CN group remained intact (Scheme 3).

The desired 4p and 4r were ﬁnally obtained from the amino

acids protected as their respective N-Boc oxazolidines 15p

and 15r,⁸via the intermediate diesters 16⁰p and 16⁰r

Figure 2. SAR of KAPA derivatives.

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1735

Table 1. P and R substituent assignments

P N-Protective group

desired cis-diamino analogs. Alas, the diamines 19⁰a and

19⁰b were obtained as equimolar mixtures of two dia-

stereomers. A similar loss of chiral discrimination was

described earlier.⁶Based on biological data (see below),

derivatives 20⁰a and 20⁰b were cyclized to the respective

DTB analogs 21⁰a and 21⁰b (Scheme 5). Since S-containing

KAPA-analogs 5⁰g–n were unsuitable to catalytic hydro-

genation due to catalyst poisoning, for these compounds an

alternative route to the DAPA structure was developed

involving reductive amination with NaBH₃CN. This

procedure was also convenient for the threonine analog

4rI. Since standard N-Boc protection of amines involves

basic conditions, to avoid possible decomposition of free

amino ketones obtained upon acid neutralization of

derivatives 4⁰, mild basic conditions coupled with sonnica-

tion were found to be satisfactory for the preparation of the

N-Boc derivatives 5⁰aI and 5⁰bI. These compounds were

amenable to subsequent NaBH₃CN reduction in organic

media. The DAPA analogs 21a and 21b were found to be

racemic at the C-7 centers (Scheme 5).⁶

Code

Boc

CBZ

MeOCO

Ac

R-substituent

H-

Me–

Et–

i-Pr–

I

II

III

IV

Code

a

b

c

d

e

f

g

h

i

j

k

l

m

n

i-Bu–

sec-Bu–

MeSCH₂CH₂–

MeS(O)CH₂CH₂–

MeSCH₂–

HSCH₂–

Boc-SCH₂–

CBZ-SCH₂–

Bn-SCH₂–

Ac-SCH₂–

CH₂vCH–

HOCH₂–

THP-OCH₂–

HOCH(Me)–

THP-OCH(Me)–

o

p

q²⁸

R

s²⁸

2.3. Vinyl derivatives

The natural vitamer, KAPA 4b, possesses a terminal R¼Me

Note: all Me esters are labeled as #⁰.

group. In these studies, the ﬁrst analog found to possess

Scheme 6. DTB and thio-DTB analogs derived from methionine.

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A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

Scheme 7. Attempted synthesis of vinyl-KAPA.

inhibitory effects on plant growth was the analog 4a where

R¼H. However when an additional carbon was added, 4c

R¼Et, no inhibition was detected. Being that a vinyl group

is larger than a Me group, yet smaller than an Et group,

introduction of a vinyl substituent at position 8 was

expected to provide additional information on the steric

demands for molecular ﬁt at this part of the molecule

(Fig. 2).

Periodate oxidation of 3⁰gI to sulfoxide 3⁰hI¹²followed by

removal of the N-Boc protective group gave the KAPA

analog 5⁰h. Because the attempted pyrolysis of 5⁰h to the

corresponding vinylic KAPA derivative failed (Scheme 7),

an alternative approach to the vinylic derivative was

developed. Reaction of 4⁰g with di-tert-butyl dicarbonate

or acetylimidazole yielded sulﬁdes 5⁰gI and 5⁰gIV, that were

oxidized to sulfoxides 5⁰hI and 5⁰hIV, respectively.

Whereas pyrolysis of 5⁰hI afforded a mixture of 5⁰oI and

23⁰I, the N-acetylated 5⁰hIV due to the higher acidity of the

methine hydrogen a to the amido group, gave only the

corresponding 23⁰IV (Scheme 8). Although in the former

case some of the desired 5⁰oI was isolated, because of

concomitant loss of the Boc group under the pyrolysis

conditions, the overall yield of the mixture of oleﬁns was

very low.

Given that ^L-alanine was the substrate for KAPA, and

glycine was used in the preparation of desmethyl-KAPA,⁹

L-vinylglycine,¹⁰1o, was the preferred starting material for

the synthesis of the 9-vinyl derivative 4o. In addition to its

enzyme-inhibitory and antibiotic properties ^L-vinylglycine

has become an important chiral starting material for a

variety of other amino acid syntheses and optically active

products. Since the attempted direct formation of the b-keto

ester of vinylglycine, analog of compound 2⁰o, failed,

apparently due to the acidity of the methine proton of

vinylglycine, the b-keto ester of methionine 2⁰gI was

prepared from N-Boc-methionine 1gI by Mansour’s

method.¹¹By analogous methodology to that described in

Scheme 1, 2⁰gI was further converted into KAPA, DAPA,

DTB and thio-DTB analogs 4g, 20⁰g, 21⁰g and 22⁰g,

respectively (Scheme 6). The lack of herbicidal activity of

these derivatives may be attributed to the presence of the

MeSCH₂-substituent on C-8, being probably too big to ﬁt

into the enzymatic ‘cavity’ suitable for a Me group.

In an attempt to avoid the isomerization of the double bond

in 5⁰oI leading to 23⁰oI, attributed to the acidity of the

proton a to the carbonyl group, sulfoxide 21⁰h, obtained by

periodate oxidation of 21⁰g, was pyrolyzed, however the

reaction was unsuccessful (Scheme 9).

To stay away from ketonic groups having acidic a-protons,

DAPA derivatives protected with groups other than N-Boc,

were examined. Sulfoxide 20⁰hII was obtained in excellent

yield when 20⁰gII suspended in MeOH was dissolved in

CH₂Cl₂, and was oxidized with NaIO₄in a mixture of

Scheme 8. Formation of isomeric vinylic derivatives of KAPA.

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1737

Scheme 9. Attempted pyrolysis of a DTB-sulfoxide derivative.

MeOH and H₂O. In the course of pyrolysis of 20⁰hII partial

loss of the CBZ groups was observed, giving a mixture of

benzyl alcohol and imidazolones 21⁰o and 24⁰o. The N on to

which the CBZ was attached in 24⁰o was not determined. In

both products only the desired terminal vinyl substituent

was found, without a trace of the undesired isomer (Scheme

10).

not conducted. Instead, herbicidal activity was measured at

difference concentrations of the compounds and the results

were recorded as GR₅₀values. The term of GR₅₀refers to

the concentration of the active compound that causes a 50%

growth inhibition. In our tests commercial herbicides gave

GR₅₀values of ,50 ppm, so compounds with activity in

this range were considered herbicidal. When compounds

described in this paper exhibited herbicidal activity, reversal

tests were carried out by treating the plants with biotin. If

the herbicidal activity of a compound was reversed by

biotin, it was deemed likely that the compound was active

because it disrupted biotin biosynthesis.

To avoid the cyclization observed in the course of the

pyrolysis, the amino groups where protected as methyl

carbamates. Although carbamates are usually prepared

using methyl chloroformate and NaOH,¹³the bis-carbamate

derivative 20⁰gIII was prepared in excellent yield using

dimethyl dicarbonate, by an analogous procedure to that

used with di-t-butyl dicarbonate. Oxidation of 20⁰gIII gave

the sulfoxide 20⁰hIII, which was pyrolyzed to give 20⁰oIII

as a mixture of two diastereomers. Whereas acidic hydroly-

sis of 20⁰oIII gave a mixture of vinylic isomers 20o and 25o

in a 9:1 ratio, basic hydrolysis led to the mono-carbamoyl-

ated cyclic urea isomers 21o and 26o where the location of

the N-carbamate was not established (Scheme 11).

Initial herbicidal activity tests were carried out on

Arabidopsis. Compounds active against Arabidopsis where

tested further tested on Lemna, Back Mexican Sweet Corn

Cells (BMS), and Barnyard grass.

In conclusion, the growth inhibitory activities (GR₅₀) of a

selected number of compounds are listed in Table 2. The

most active compound found was desmethyl-KAPA 4a.

Other KAPA analogs where the terminal Me group was

replaced by bulkier substituents such as Et, i-Pr and HOCH₂

showed moderate activity, whereas the thio-derivatives

(HSCH₂, MeSCH₂and Me₂CH₂CH₂) as well as that derived

2.4. Biological results

Enzyme assays on compounds described in this paper were

Scheme 10. Pyrolysis of a di-Cbz-DAPA sulfoxide derivative.

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A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

Scheme 11. Attempted formation of 9-vinyl-DTB.

from threonine (MeCHOH) were considerably weaker

inhibitors. DAPA and DTB analogs replacing the Me by

H or Et also showed moderate activity. When comparing

free acids to their respective more lipophilic Me esters, the

latter where found to be more active. Subsequent reports

will describe the inhibitory activity of isosters involving

additional structural modiﬁcations based on the natural

vitamers.

incubator under continuous ﬂuorescent lighting with an

intensity of 55 mE m²²s²¹. The plants were rated after

three weeks against the controls for growth inhibition due

to the inhibitor treatment. These ratings were used to

determine the GR₅₀value, which is the concentration that

resulted in a 50% growth reduction.

To obtain more tissue for biotin determinations, seven-day

old Arabidopsis seedlings grown on media without the

inhibitor were watered over the foliage with different

concentrations of the tested inhibitor in 8 mM phosphate

buffer, at a pH 6.5 value. Plants were harvested at 0, 7 and

14 days after treatment and were weighed and extracted for

total biotin determination.

3. Experimental

3.1. Biology—methods and materials

3.1.1. Arabidopsis test. Arabidopsis thaliana was grown in

12-well titer plates under sterile conditions on 0.8% agar

medium containing nutrient solution as described by

Somerville and Ogren.¹⁴Concentrated treatment solutions

were ﬁlter sterilized and were added to the agar solution

while it was still in a liquid state (45 8C). Three mL aliquots

of the agar solution were pipetted into the wells. Con-

centrated treatment solutions were ﬁlter sterilized and were

added to the agar solution while it was still in a liquid state

(45 8C). When the agar had solidiﬁed and cooled, seeds

were sown on the surface. The plates were placed in a 26 8C

3.2. Chemistry—general

¹H NMR spectra 200 and 300-MHz were obtained on

Bruker AC-200 and AM-300 spectrometers, respectively.

Chemical shifts are expressed in ppm downﬁeld from Me₄Si

used as internal standard. When D₂O was used as solvent, its

own peak was used as internal standard for ¹H NMR, while

additional MeOH was used as an internal standard for ¹³C

NMR. The values are given in d scale. Mass spectra were

obtained on a Varian Mat 731 spectrometer (CI¼chemical

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

Table 2. Growth inhibitory activity (GR₅₀) of selected isosters of the biotin vitamers

1739

Compounds

Structure

GR₅₀(ppm)

8

Compounds

Structure

GR₅₀(ppm)

40

4a²⁹

18b⁶

4c³⁰

43

37

18c

18d

.780

4d

4g

4i

.780

250

20a³¹

53

76

20⁰c

4⁰i

4j

20⁰g

.780

35

.780

21a²⁶

4⁰j

120

100

53

21c²⁷

21g

21i

35

.780

46

4p

4⁰p

4r²⁰

4⁰r²⁰

18a

250

100

53

22⁰g

22⁰i

.780

44

ionization). HRMS were obtained on a VG AutoSpec E

spectrometer. Progress of the reactions was monitored by

TLC on silica gel (Merck, Art. 5554) or alumina (Riedel-de

Haen, Art. 37349). Flash chromatography was carried out

on silica gel (Merck, Art. 9385). Commercially available

chemicals were used without further puriﬁcation.

3.3. N-Boc protection of amino acids 1

Method A.¹⁵To a stirred solution of an amino acid

(0.03 mol) and NaOH (0.03 mol) in water (4 mL) and tert-

BuOH (6 mL) was added di-tert-butyl dicarbonate

(0.03 mol). The mixture was stirred overnight at room

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A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

temperature, water (15 mL) was then added and the aqueous

phase was washed with hexane (3£50 mL). The aqueous

phase was acidiﬁed with KHSO₄(to pH¼2.5), extracted

with EtOAc (4£50 mL). The combined organic layers were

dried (MgSO₄), ﬁltered and evaporated to afford the desired

N-Boc protected amino acid.

1.3 mmol) was added dropwise to a solution of an N-pro-

tected amino acid (1 mmol) in hexane (5 mL) and

anhydrous MeOH (2 mL). The mixture was stirred at

room temperature overnight, and became cloudy. The

solvent was evaporated and the residue was dissolved in

CHCl₃and was washed with 5% NaHCO₃. The aqueous

layer was extracted with CHCl₃(2£) and the combined

organic layers were dried (MgSO₄), ﬁltered and evaporated,

to give the esters. Although it was not required to wash the

product with 5% NaHCO₃, this was found convenient to

obtain the product without a trace of the starting acid.

Method B.¹⁶A suspension of a KAPA.HCl methyl ester

derivative (1 mmol), NaHCO₃(3 mmol), and di-tert-butyl

dicarbonate (1 mmol) in dry MeOH (10 mL), was sonicated

at room temperature for 6 h. The resulting mixture was

ﬁltered and evaporated to dryness. The residue was

dissolved in ether (20 mL) and 1 N HCl (20 mL). The

aqueous layer was washed with ether (3£15 mL). The

combined organic layer was washed with 5% NaHCO₃

(2£20 mL), and brine (2£20 mL). The organic phase was

dried (MgSO₄), ﬁltered and evaporated to give the desired

N-Boc product.

3.6. Conversion of N-protected amino acid derivatives to

the corresponding b-keto esters

To a solution of an N-protected amino acid (1 mmol) in dry

THF (10 mL) under N₂, CDI (1.2 mmol) was added portion

wise. The mixture was stirred at room temperature for 1 h,

then MgCl₂(1 mmol) and monomethyl malonate K salt

(1 mmol) were added at once. The mixture was stirred at

35 8C overnight. The resulting slurry was ﬁltered and the

ﬁltrate was evaporated. The residue was dissolved in EtOAc

(20 mL) and 1 N HCl (20 mL). The aqueous phase was

extracted with EtOAc (3£20 mL). The organic layers were

washed with 5% NaHCO₃(2£20 mL), brine (20 mL). The

organic layer was dried (MgSO₄) and evaporated to give the

desired product.

Method C.¹⁷To a solution of L-cystine (4 mmol), NaOH

(8 mmol) in 15 mL water at 0 8C, was slowly added DMF

(15 mL). The mixture was brought to room temperature

and di-tert-butyl dicarbonate (8 mmol) was added in one

portion. The pH was maintained at ,9 by adding NaOH for

3 h and stirring at room temperature was continued over-

night. To the cloudy mixture, water (50 mL) was added and

was washed with EtOAc (2£50 mL). To the aqueous

solution obtained, EtOAc was added (50 mL). The mixture

was cooled to 0 8C and HCl 1 N was added until pH 3 was

obtained. The organic phase was separated and washed with

water (6£20 mL). The organic phase was dried (MgSO₄),

ﬁltered and evaporated to give the desired product.

3.6.1. 4-tert-Butoxycarbonylamino-3-oxo-hexanoic acid

methyl ester (2⁰cI). From N-Boc-dl-2-aminobutyric acid,

0

1

1 cI (60% yield). H NMR (CDCl₃) d 0.93 (d, J¼7.5 Hz,

3H, CH₂Me), 1.45 (s, 9H, Me₃C), 1.61 (m, 1H, CH₂Me),

1.95 (m, 1H, CH₂Me), 3.57 (ABq, J¼15 Hz, 2H, CH₂CO),

3.75 (s, 3H, OMe), 4.32 (m, 1H, CHNH), 5.16 (m, 1H, NH);

¹³C NMR (CDCl₃) d 9.5 (CH₂Me), 24.1 (CH₂Me), 28.3

(Me₃C), 46.1 (CH₂CO), 52.4 (OMe), 60.8 (CHNH), 80.1

(C), 155.4 (HNCO₂), 167.2 (CO₂Me), 201.9 (CO); MS (EI)

m/e 260 (MH^þ, 34), 204 (MH^þ2C₄H₈, 100), 186 (MH^þ2

t-BuOH, 17), 160 (MH^þ2Boc, 68); HRMS (DCI, CH₄)

calcd for C₁₂H₂₂NO₅(MH^þ) 260.1497 found 260.1420.

Method D. A mixture of the amino acid ester derivative

(1 mmol) and Et₃N (1 mmol) in dry CH₂Cl₂(10 mL) was

stirred at room temperature for 10 min. Di-tert-butyl

dicarbonate (1 mmol) was added and the reaction mixture

was stirred at room temperature for 18 h. The resulting

mixture was washed with water (3£25 mL). The organic

layer was dried (MgSO₄), ﬁltered and evaporated to dryness,

to afford the desired product.

3.6.2. 3-(3-Formyl-2,2-dimethyl-thiazolidin-4-yl)-3-oxo-

propionic acid methyl ester (8⁰). From 2,2-dimethyl-

3.4. 2-(3-Formyl-2,2-dimethyl-thiazolidine-4-carbonyl)-

heptanedioic acid 7-ethyl ester 1-methyl ester (9⁰)

thiazolidine-4-carboxylic acid hydrochloride,

7 (76%

yield). Note: dry DMF (ca. 0.5 mL) was added to the

mixture, to allow better solubility of the starting acid. The

product was obtained as a single isomer, derived from

the major rotamer of the starting material. ¹H NMR (CDCl₃)

C-Alkylation of 8⁰with ethyl 5-iodovalerate (53% yield).

Note: due to large amounts of O-alkylation products, only

one equivalent of K₂CO₃in 2-butanone (bp 73 8C) was

1

used. H NMR (CDCl₃) d 1.23 (t, J¼7 Hz, 3H, CH₂Me),

d 1.84 (s, 6H, Me₂C), 3.30 (ABq of d, J_AB¼12.2 Hz, J_AX¼

1.38 (m, 2H, CH₂CH₂CH₂CO₂), 1.63 (superimposed, 5H,

MeC and CH₂(CH₂)₃CO₂), 1.81 (superimposed, 5H, MeC

and CH₂CH₂CO₂), 2.30 (t, J¼7.5 Hz, 2H, CH₂CO₂), 3.23

(ABq of d, J_AB¼13.8 Hz, J_AX¼5 Hz, J_BX¼4.8 Hz, 2H,

SCH₂), 3.74 and 3.75 (two s, 3H, OMe), 3.75 and 3.93 (two

t, J¼7 Hz, 1H, COCHCO₂), 4.12 (q, J¼7 Hz, 2H, CH₂Me),

4.92 (td, J¼7, 1 Hz, 1H, CHNH), 8.20 (d, J¼1 Hz, 1H,

COH).

7 Hz, J_BX¼6 Hz, 2H, CH₂S), 3.70 (ABq, J_AB¼16.1 Hz, 2H,

CH₂CO), 3.75 (s, 3H, OMe), 5.04 (ddd, J¼7, 6, 1 Hz, 1H,

CH₂CH), 8.29 (d, J¼1 Hz, 1H, CHO). ¹³C NMR (CDCl₃) d

30.1 (CH₂S), 30.9 (MeC), 31.5 (MeC), 46.9 (CH₂CO), 52.3

(OMe), 68.1 (CHCH₂), 70.3 (Me₂C), 158.90 (CON), 167.3

(CO₂), 198.6 (COCH). MS (CI/NH₃) m/e 263 (MNH^þ₄, 100),

246 (MH^þ, 37).

6

3.7. C-Alkylation of b-keto esters using K₂CO₃

3.5. General procedure for the preparation of methyl

esters, using a diazomethane derivative, trimethylsilyl

diazomethane¹⁸

To a solution of a b-keto ester derivative (1 mmol) in dry

acetone (20 mL) and anhydrous K₂CO₃(4 mmol) or dry

2-butanone (MEK) (20 mL) and K₂CO₃(1 mmol), was

added an alkyl iodide (1 mmol). The resulting suspension

A 2 M solution of TMS-diazomethane in hexane (0.65 mL,

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1741

1

was reﬂuxed under nitrogen for 6–18 h, cooled and ﬁltered.

The salts were washed with acetone. The ﬁltrate was

evaporated and the residue was ﬂash chromatographed on

a silica gel column (hexane/EtOAc 2:1 or 3:1), to give

the desired C-alkylated product, containing mixtures of

diastereomers.

yield). H NMR (D₂O) d 1.32 (m and d, superimposed,

J¼6.6 Hz, 5H, Me, CH₂CH₂CH₂CO₂), 1.49–1.66 (m, 4H,

CH₂CH₂CH₂CH₂CO₂), 2.34 (t, J¼7.3 Hz, 2H, CH₂CO₂),

2.70 (dt, J¼2.5, 7.2 Hz, 2H, CH₂CO), 4.22 (d, J¼2.5 Hz,

1H, CHN), 4.60 (dq, J¼2.5, 6.6 Hz, 1H, CHMe); ¹³C NMR

(D₂O) d 19.68 (Me), 22.79 (CH₂CH₂CO₂), 24.43 (CH₂-

CH₂CO), 28.06 (CH₂(CH₂)₂CO₂), 34.06 (CH₂CO₂), 39.33

(CH₂CO), 64.44 (CHMe), 64.89 (CHN), 179.18 (CO₂),

207.53 (CO); MS (CI, NH₃) m/e 218 (MH^þ, 18), 200

(MH^þ2H₂O, 12), 174 (MH^þ2CO₂, 15); HRMS (DCI, CH₄)

calcd for C₁₀H₂₀NO₄(MH^þ) 218.1392 found 218.1390.

3.7.1. 2-tert-Butoxycarbonylaminoacetyl-heptanedioic

acid 7-ethyl ester 1-methyl ester (3⁰aI). From 2⁰aI (55%

yield). ¹H NMR (CDCl₃) d 1.25 (t, J¼7 Hz, 3H, OCH₂Me),

1.45 (s, 9H, Me₃C), 1.50–1.78 (m, 4H, CHCH₂CH₂CH₂),

1.90 (m, 2H, CHCH₂CH₂CH₂), 2.30 (t, J¼7 Hz, 2H,

CH₂CO₂Et), 3.50 (t, J¼7 Hz, 1H, CHCO₂Me), 3.73 (s,

3H, OMe), 4.15 (m, superimposed, 4H, CH₂NH, OCH₂Me),

5.20 (m, 1H, NH); ¹³C NMR (CDCl₃) d 14.2 (OCH₂Me),

24.4 (CH₂CH₂CO₂), 25.1 (CHCH₂), 26.8 (CHCH₂CH₂),

28.3 (Me₃C), 33.9 (CH₂CO₂), 50.1 (CH₂NH), 52.6 (OMe),

55.9 (CHCO₂Me), 60.3 (OCH₂Me), 80.0 (C), 155.5

(HNCO₂), 169.4 (CO₂Me), 173.2 (CO₂Et), 200.9 (CO);

MS (CI, i-Bu) m/e 360 (MH^þ, 1), 304 (MH^þ2C₄H₈, 13),

256 (MH^þ2Boc, 100); HRMS (DCI, CH₄) calcd for

C₁₇H₃₀NO₇(MH^þ) 360.2022 found 360.1995.

3.8.4. 8-Amino-9-hydroxy-7-oxo-nonanenitrile hydro-

chloride (14p). From 13⁰qI. The reaction mixture was

washed with EtOAc (2£10 mL) and then the aqueous

solution was evaporated to afford the product (60% yield).

¹H NMR (D₂O) d 1.40 (m, 2H, CH₂(CH₂)₂CN), 1.61 (m,

4H, CH₂CH₂CH₂CH₂CN), 2.44 (t, J¼7 Hz, 2H, CH₂CN),

2.70 (t, J¼7 Hz, 2H, CH₂CO), 4.05 (dd, J¼3.4, 12.8 Hz, 1H,

CH₂OH), 4.17 (dd, J¼4, 12.8 Hz, 1H, CH₂OH), 4.35 (t,

J¼3.7 Hz, 1H, CHCH₂); ¹³C NMR (D₂O) d 16.8 (CH₂CN),

22.3 (CH₂CH₂CN), 24.7 (CH₂CH₂CO), 27.8 (CH₂(CH₂)_2-

CN), 38.9 (CH₂CO), 59.4 (CH₂OH), 61.3 (CHN), 122.7

(CN), 207.1 (CO).

3.8. Preparation of KAPA·HCl derivatives (hydrolysis

and decarboxylation of compounds 3)⁶

3.9. Formation of methyl esters of amino acids 4

A suspension of a C-alkylated ester 3 (1 mmol) in 4 N HCl

(2 mL) was reﬂuxed for 2 h. Gas evolution was observed.

The resulting dark yellow solution was evaporated under

high vacuum. If the color of the resulting product darkened,

the residue was dissolved in distilled water (minimum

amount) and was treated with charcoal, ﬁltered and the

ﬁltrate was evaporated under high vacuum to give a solid

residue. Recrystallization was carried out from EtOH–

ether, or ether–HCl, to give the desired HCl salt.

Method A. Concentrated HCl (1.12 mL) was added to a

solution of a KAPA derivative (1 mmol) in 2,2-dimethoxy-

propane (15 mL). The mixture was stirred at room

temperature overnight. The solvent was evaporated and

the residue was dissolved in a small amount of MeOH.

Addition of dry ether resulted in crystallization. The crystals

were ﬁltered and washed with ether to give hydrochloride

salt.

3.8.1. 8-Amino-7-oxo-octanoic acid hydrochloride (4a).¹⁹

Method B. A solution of a KAPA·HCl derivative (1 mmol)

in MeOH·HCl (8 mL) was stirred at room temperature

overnight. Evaporation under vacuum gave the hydro-

chloride salt.

Hydrolysis and decarboxylation of 3⁰aI, isolated as a

1

white solid mp 129–131 8C (84% yield). H NMR (D₂O)

d 1.40 (m, 2H, CH₂CH₂CH₂CO₂), 1.70 (m, 4H, CH₂CH₂-

CH₂CH₂CO₂), 2.40 (t, J¼7 Hz, 2H, CH₂CO₂), 2.70

(t, J¼7 Hz, 2H, CH₂CO), 4.18 (s, 2H, CH₂N); ¹³C NMR

(D₂O) d 22.9 (CH₂CH₂CO₂), 24.6 (CH₂CH₂COCH), 28.2

(CH₂CH₂CH₂CO), 34.4 (CH₂CO₂), 39.9 (CH₂COCH), 47.7

(CH₂N), 180.0 (CO₂), 206.9 (CO); MS (CI, NH₃) m/e 174

(MHþ, 100); HRMS (DCI, CH₄) calcd for C₈H₁₆NO₃

(MH^þ) 174.1130 found 174.1140.

Method C. To a solution of a KAPA derivative (1 mmol) in

dry MeOH (10 mL) at 0 8C was dropwise added AcCl

(3 mL).²⁰The resulting mixture was stirred at room

temperature overnight. Evaporation yielded the hydro-

chloride salt.

3.9.1. 8-Amino-7-oxo-octanoic acid methyl ester hydro-

chloride (5⁰a). Esteriﬁcation of DMK·HCl 4a (quantitative

yield). H NMR (D₂O) d 1.30 (m, 2H, CH₂CH₂CH₂CO₂),

3.8.2. 8-Amino-9-methyl-7-oxo-decanoic acid hydro-

0

1

chloride (4d). From 3 dI (95% yield). H NMR (D₂O) d

0.86 (d, J¼7 Hz, 3H, Me), 1.11 (d, J¼7 Hz, 3H, Me), 1.33

(m, 2H, CH₂(CH₂)₂CO₂), 1.60 (m, 4H, CH₂CH₂CH₂CH₂-

CO₂), 2.37 (t, J¼7.5 Hz, 2H, CH₂CO₂), 2.55 (m, 2H,

CHMe₂), 2.68 (m, 2H, superimposed, CH₂CO), 4.24 (d,

J¼3.5 Hz, 1H, CHN); ¹³C NMR (D₂O) d 15.8 (Me), 19.0

(Me), 22.8 (CH₂(CH₂)₃CO₂), 24.6 (CH₂CH₂CO₂), 28.6

(CHMe₂), 34.4 (CH₂CO₂), 39.7 (CH₂CO), 64.7 (CHCO),

177.7 (CO₂), 209.6 (CO); MS (DCI, NH₃) m/e 216 (MH^þ,

100); HRMS (DCI, CH₄) calcd for C₁₃H₂₆NO₃(MH^þ)

244.1912 found 244.1918.

1.60 (m, 4H, CH₂CH₂CH₂CH₂CO₂), 2.40 (t, J¼7.3 Hz, 2H,

CH₂CO₂), 2.60 (t, J¼7.4 Hz, 2H, CH₂CO), 3.70 (s, 3H,

OMe), 4.05 (s, 2H, CH₂N); ¹³C NMR (D₂O) d 22.8

(CH₂CH₂CO₂), 24.5 (CH₂CH₂CO), 28.2 (CH₂CH₂CH₂-

CO₂), 34.0 (CH₂CO₂), 39.9 (CH₂CO), 52.7 (OMe), 58.1

(CH₂N), 178.0 (CO₂Me), 209.8 (CO); MS (CI, i-Bu) m/e

187 (MH^þ2HCl); HRMS (DCI, CH₄) calcd for C₉H₁₈NO₃

(MH^þ) 188.1286 found 188.1260.

3.9.2. 8-Acetylamino-10-methylsulfanyl-7-oxo-decanoic

acid methyl ester (5⁰gIV). N-Acetylation of 4⁰g—CDI

(0.22 g, 1.3 mmol) was added to a solution of AcOH

(0.08 g, 1.3 mmol) in dry THF (10 mL) under N₂. The

3.8.3. 8-Amino-9-hydroxy-7-oxo-decanoic acid hydro-

chloride (4r). Hydrolysis and decarboxylation of 17⁰b (96%

1742

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

mixture was stirred at room temperature for 1 h and was

transferred via a cannula to a ﬂask containing 4⁰g (0.35 g,

1.16 mmol). The mixture was stirred at room temperature

under N₂overnight and was evaporated. The residue was

partitioned between 1 N HCl and EtOAc and the aqueous

layer was extracted with EtOAc (4£). The combined

organic layers were washed with 5% NaHCO₃(2£), brine,

dried (MgSO₄), ﬁltered and evaporated to give 5⁰gIV as an

oil, 57% yield). ¹H NMR (CDCl₃) d1.34 (m, 2H,

CH₂(CH₂)₂CO₂), 1.64 (m, 4H, CH₂(CH₂)₃CO₂), 2.04 (s,

3H, MeCO), 2.10 (s, 3H, SMe), 2.27 (m, 2H, SCH₂CH₂),

2.32 (t, J¼7.4 Hz, 2H, CH₂CO₂), 2.50 (superimposed, m,

4H, CH₂S and CHCOCH₂), 3.67 (s, 3H, OMe), 4.74 (td,

J¼7.5, 4.5 Hz, 1H, CH), 6.30 (brd, J¼6.2 Hz, 1H, NH). MS

(CI/i-Bu) m/e 304 (MH^þ, 100), 272 (MH^þ2MeOH, 51),

229 (MH^þ2MeSCH₂CH₂, 71), 146 (91), 104 (67); HRMS

(CI/CH₄) calcd for C₁₄H₂₆NO₄S (MH^þ), 304.06436 found

304.04163.

The obtained suspension was ﬁltered, evaporated, and the

crude residue was puriﬁed by ﬂash chromatography

(hexane/EtOAc usually 2:1).

3.10.1. 2-(2-tert-Butoxycarbonylamino-propionyl)-6-

cyano-hexanoic acid methyl ester (13⁰b). From 1bI and

12 The product was obtained as a mixture of two

1

diastereomers, 23% yield). H NMR (CDCl₃) d 1.34 (two

d, J¼7.2 Hz, 3H, Me), 1.44–1.45 (two s, 9H, t-Bu), 1.44 (m,

2H, CH₂(CH₂)₂CN), 1.67 (quintet, J¼7.4 Hz, 2H, CH₂CH),

1.89 (quintet, J¼7.4 Hz, 2H, CH₂CH₂CN), 2.36 (t, J¼7 Hz,

2H, CH₂CN), 3.73 (s and m, superimposed, 4H, OMe,

CHCO₂), 4.39 (m, 1H, CHMe), 5.11 (bt, J¼7.6 Hz, 1H,

NH); ¹³C NMR (CDCl₃) d16.7 and 16.8 (CHMe), 17.4

(CH₂CN), 25.0 and 25.1(CH₂CH₂CN), 26.3 and 26.4

(CHCH₂CH₂), 28.2 (Me₃C), 27.6 and 27.9 (CHCH₂), 52.4

(CHCO₂), 52.46 and 52.52 (OMe), 54.9 (CHMe), 80.01 (C),

119.2 (CN), 155.0 (CO₂NH), 169.4 (CO₂Me), 204.4 (CO);

MS (CI, NH₃) m/e 344 (MNH^þ₄, 100), 327 (MH^þ, 10.9),

288 (MNH₄^þ2C₄H₈, 74), 271 (MH^þ2C₄H₈, 7), 227

(MH^þ2Boc, 11); HRMS (DCI, CH₄) calcd for

C₁₆H₂₇N₂O₅(MH^þ) 327.1920 found 327.1840.

3.9.3. 2-(4-Cyanobutyl)-malonic acid dimethyl ester

(11).²¹Dimethyl malonate (0.02 mol, 2.64 g) in MeOH

(5 mL) was added to an ice-cold solution obtained by

addition of NaH (60% in oil, 0.02 mol, 0.98 g) to dry MeOH

(20 mL). The mixture was stirred for a few minuets at room

temperature and then 5-bromovaleronitrile (0.02 mol,

3.25 g) dissolved in MeOH (5 mL) was added followed by

addition of a catalytic amount of KI. The mixture was

reﬂuxed for 48 h, ﬁltered and evaporated. The inorganic

salts were dissolved in water (20 mL) and were washed with

EtOAc (3£20 mL). The organic phase was dried (MgSO₄),

ﬁltered and evaporated and the residue was ﬂash chromato-

graphed (hexane/EtOAc 2:1), to give the C-alkylated

product 30% yield. ¹H NMR (CDCl₃) d 1.47 (quintet,

J¼7 Hz, 2H, CH₂(CH₂)₃CN), 1.70 (quintet, J¼7 Hz, 2H,

CH₂(CH₂)₂CN), 1.93 (q, J¼7.5 Hz, 2H, CH₂CH₂CN), 2.37

(t, J¼7 Hz, 2H, CH₂CN), 3.37 (t, J¼7.4 Hz, 1H, CH), 3.74

(s, 6H, OMe); ¹³C NMR (CDCl₃) d16.7 (CH₂CN), 24.8

(CH₂CH₂CN), 26.1 (CHCH₂), 51.1 (OMe), 52.3 (CH),

119.1 (CN), 169.3 (CO₂Me); MS (CI, NH₃) m/e 231

(MNH₄^þ, 100), 214 (MH^þ, 6); HRMS (DCI, CH₄) calcd for

C₁₀H₁₆NO₄(MH^þ) 214.1079 found 214.1074.

3.10.2. 2-[2-tert-Butoxycarbonylamino-3-(tetrahydro-

pyran-2-yloxy)-propyl]-6-cyano-hexanoic acid methyl

ester (13⁰qI). From 1q and 12. The product was obtained

1

as a mixture of two diastereomers, 18% yield). H NMR

(CDCl₃) d 1.46 (s, 9H, Me₃C), 1.46–1.94 (m, 12H, (CH₂)

₃CH and (CH₂)₃CH₂CN), 2.35 (t J¼7 Hz, 2H, CH₂CN),

3.60 (m, 2H, CH₂CHN), 3.70 and 3.71 and 3.73 and 3.74

(four s, 3H, OMe), 3.85 (m, 3H, CH₂OCH and CHCOO),

4.59 (m, 2H, CHNH and OCHO), 5.63–5.38 (m, 1H, NH);

¹³C NMR (CDCl₃) d 16.9 (CH₂CN), 19.3 and 19.6 and 19.7

(CH₂CH₂CH), 25.2 (CH₂CH₂CN), 26.4 and 26.5 and 26.8

and 26.9 (CH₂CH₂O and CH₂(CH₂)₂CN), 27.2 and 27.5

(CH₂(CH₂)₃CN), 28.3 (Me₃C), 30.3 and 30.4 and 30.5

(CH₂CHO), 52.4 and 52.6 (OMe), 54.8 and 55.0 and 55.2

and 55.4 (CHCO₂), 59.0 and 59.4 and 59.7 and 60.4

(CHNH), 62.3 and 62.8 and 63.0 (CH₂OCH), 67.1 and 67.7

and 68.9 (CH₂O), 80.1 and 80.3 (C), 99.2 and 99.5 and 99.9

(OCHO), 119.3 (CN), 155.4 (NHCO₂), 169.2 and 169.3

(CO₂OMe), 202.2 and 203.5 (CO); MS (CI, NH₃) m/e 444

(MNH₄^þ, 100), 427 (MH^þ, 6), 388 (MNH₄^þ2C₄H₈, 21),

360 (MNH₄^þ2C₅H₈O, 85), 343 (MNH₄^þ2HBoc, 32).

3.9.4. 2-(4-Cyanobutyl)-malonic acid monomethyl ester

potassium salt (12). KOH (1 mmol) in MeOH (5 mL) was

added to a stirred solution of 11 (1 mmol) in MeOH (2 mL).

The mixture was stirred overnight, and was then evaporated

to dryness to give the product in quantitative yield. ¹H NMR

(CDCl₃) d 1.45 (m, 2H, CH₂(CH₂)₂CN), 1.63 (m, 2H,

CH₂(CH₂)₃CN), 1.88 (m, 2H, CH₂CH₂CN), 2.41 (t, J¼

6.7 Hz, 2H, CH₂CN), 3.18 (t, J¼6.2 Hz, 1H, CH), 3.71

(s, 3H, OMe); ¹³C NMR (CDCl₃) d16.9 (CH₂CN), 25.0

(CH₂CH₂CN), 27.0 (CHCH₂CH₂), 29.1 (CHCH₂), 52.0

(OMe), 55.5 (CH), 120.6 (CN), 174.2 (CO₂²), 174.7

(CO₂Me); MS (CI, NH₃) m/e 173 (MNH₄^þ2CO₂K, 100),

214 (MH^þ, 6).

3.10.3. 2-(2-tert-Butoxycarbonylamino-3-hydroxy-

butyryl)-6-cyano-hexanoic acid methyl ester (13⁰r). In

the course of the workup of the previous reaction, the THP

protective group was removed. The product was obtained as

a mixture of two diastereomers, 12% yield. ¹H NMR

(CDCl₃) d 1.25 (d, J¼6.3 Hz, 3H, CHMe), 1.47 (s, 9H,

Me₃C), 1.70 (m, 4H, (CH₂)₂(CH₂)₂CN), 1.92 (m, 2H,

CH₂CH₂CN), 2.36 (t J¼7 Hz, 2H, CH₂CN), 3.37 (t, J¼

7.4 Hz, 1H, CHMe), 3.73 (m, 1H CHCO₂), 3.75 (s, 3H,

OMe), 4.31 (m, 1H, CHNH), 5.33 (m, 1H, NH); ¹³C NMR

(CDCl₃) d 16.9 (CH₂CN), 19.9 (CHMe), 25.1 (CH₂(CH₂)₃-

CN), 26.4 (CH₂(CH₂)₂CN), 28.0 (CH₂CH₂CN), 28.3 (Me₃C),

51.3 (CHCO₂), 52.6 (OMe), 68.2 (CHMe), 80.2 (C), 119.3

(CN), 169.5 (NHCO₂), 171.9 (CO₂OMe), 205.0 (CO).

3.10. Acylation of N-Boc-amino acids with 12

To a solution of an N-Boc-amino acid (0.84 mmol) in dry

THF (5 mL), CDI (1 mmol) was added portion wise and the

obtained mixture was stirred at room temperature for 1 h.

MgCl₂(0.84 mmol) and 12 (0.84 mmol) were then added

and the resulting mixture was stirred under reﬂux overnight.

3.11. Oximation of KAPA·HCl analogs²²

To a solution of NH₂OH·HCl (1.5 mmol) in dry pyridine

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1743

(0.75 mL) was added to an ice-cold solution of a KAPA·HCl

derivative (1 mmol) in dry pyridine (0.75 mL). The mixture

was stirred at room temperature for 24 h and was then

evaporated to dryness. The residue was dissolved in distilled

water (3 mL) and was basiﬁed with 0.5 N NaOH to pH¼8.

This solution was extracted with CH₂Cl₂(6£5 mL). The

aqueous phase was evaporated yielding the desired product.

J¼7 Hz, 2H, CH₂CO₂), 3.42 (m, 1H, CHCHMe₂), 3.70 (s,

3H, OMe), 3.82 (m, 1H, CHN); ¹³C NMR (D₂O) d 17.0

(Me), 17.5 (Me), 19.6 (CH₂Me₂), 24.4 (CH₂(CH₂)₃CO₂),

24.6 (CH₂CH₂CO₂), 27.8 (CH₂(CH₂)₂CO₂), 28.2 (CH₂-

(CH₂)₄CO₂Me), 34.1 (CH₂CO₂), 51.6 (CH(CH₂)₅), 52.3

(CHCHMe₂), 58.9 (OMe), 179.2 (CO₂Me); MS (DCI, NH₃)

m/e 231 (MH^þ, 100); HRMS (DCI, CH₄) calcd for

C₁₂H₂₇N₂O₂(MH^þ) 231.2072 found 231.2110.

3.11.1. 8-Amino-7-hydroxyimino-octanoic acid hydro-

1

chloride (18a). Oximation of 4a (98% yield). H NMR

(D₂O) d 1.32–1.36 (m, 2H, CH₂CH₂CH₂CO₂), 1.55 (m, 4H,

CH₂CH₂CH₂CH₂CO₂), 2.20 (t, J¼7.3 Hz, 2H, CH₂CO₂),

3.13. Preparation of DAPA derivatives 20 via sodium

cyanoborohydride reductive amination of ketones 5²³

2.41 (t, J¼7.5 Hz, 2H, CH₂CNOH), 3.80 (s, 2H, CH₂N); ¹³

C

To a solution of an N-Boc-KAPA derivative methyl ester

(1 mmol) in dry MeOH (10 mL), NH₄OAc (10 mmol) was

added. The solution obtained was stirred at room tempera-

ture for 10 min, then NaBH₃CN (3.7 mmol) was added in

one portion and the resulting mixture was stirred at room

temperature for 48 h. The reaction was quenched with 1 N

HCl (20 mL). The solvent was evaporated and the crude

residue was dissolved in water. KOH was added till a basic

solution was obtained. The aqueous phase was extracted

with CH₂Cl₂(3£20 mL). The combined organic layer was

washed with brine (2£10 mL), dried (MgSO₄), ﬁltered and

evaporated to give the compound.

NMR (D₂O) d 24.8 (CH₂CH₂CO₂), 25.8 (CH₂CH₂CNOH),

26.2 (CH₂CNOH), 29.0 (CH₂CH₂CH₂CO₂), 37.4 (CH₂CO₂),

41.2 (CH₂N), 158.0 (CNOH), 183.6 (CO₂); MS (CI, NH₃)

m/e 206 (MNH^þ₄, 2), 189 (MH^þ, 48).

3.11.2. 8-Amino-7-hydroxyimino-10-methyl-undecanoic

acid hydrochloride (18e). Hydrolysis and decarboxylation

1

of 3e followed by in situ oximation (34% yield). H NMR

(D₂O) d 0.98 (m, 7H, CHMe₂), 1.40 (m, 2H, CH₂CHMe₂),

1.72 (m, 8H, (CH₂)₄CO₂), 2.22 (t, J¼7.3 Hz, 2H, CH₂CO₂),

4.05 (m, 1H, CHNH₃^þ); MS (CI, NH₃) m/e 245 (MH^þ, 67),

159 (MH^þ2C₅H₁₁N, 100).

3.13.1. 7-Amino-8-tert-butoxycarbonylamino-octanoic

acid methyl ester (19⁰aI). Reductive amination of 5⁰aI

(74% yield). H NMR (CDCl₃) d 1.33 (m, 4H, (CH₂)₂-

3.12. Preparation of DAPA derivatives 20 via catalytic

reduction of KAPA oximes analogs 18⁶

1

(CH₂)₂CO₂), 1.44 (s, 9H, Me₃C), 1.62 (m, 4H, CH₂(CH₂)₂-

CH₂CH₂CO), 1.78 (m, 2H, NH₂), 2.31 (t, J¼7.5 Hz, 2H,

CH₂CO₂), 2.86 (m, 2H, CH₂NH), 3.26 (m, 1H, CH), 3.67 (s,

3H, OMe), 4.98 (m, 1H, NH); ¹³C NMR (CDCl₃) d 24.8

(CH₂(CH₂)₃CO₂), 25.7 (CH₂CH₂CO₂), 28.4 (Me₃C), 29.2

(CH₂(CH₂)₂CO₂), 34.0 (CH₂CO₂), 35.5 (CHCH₂CH₂),

47.0 (CH₂NH), 51.3 (OMe), 51.5 (CH), 79.3 (C), 156.3

(CO₂NH), 174.2 (CO₂Me); MS (CI, NH₃) m/e 289 (MH^þ,

100), 233 (MH^þ2C₄H₈, 18), 189 (MH^þ2Boc, 4); HRMS

(DCI, CH₄) calcd for C₁₄H₂₉N₂O₄(MH^þ) 289.2127 found

289.2140.

A solution of the oxime analog (1 mmol) and 4 N HCl

(2 mL) in absolute MeOH (10 mL) was hydrogenated in a

Parr apparatus at 65 psi/40 8C/48 h over 10% PtO₂(30 mg).

The mixture was ﬁltered through celite and washed with

MeOH. The solvent was evaporated yielding the diamine

product.

3.12.1. 7,8-Diamino-octanoic acid methyl ester dihydro-

chloride (20⁰a). Catalytic reduction of 18⁰a (87% yield). ¹H

NMR (D₂O) d 1.43 (m, 4H, CH₂CH₂CH₂CH₂CO₂), 1.62

(m, 2H, CH₂CH₂CH), 1.75 (m, 2H, CH₂CH₂CO₂), 2.41 (t,

J¼7.3 Hz, 2H, CH₂CO₂), 3.33 (d, J¼6.2 Hz, 2H, CH₂N),

3.63 (m, 1H, CH₂N), 3.68 (s, 3H, OMe); ¹³C NMR (D₂O) d

24.3 and 24.4 (CH₂CH₂CH₂CH₂CO₂), 28.3 (CH₂CH₂CH₂-

CO₂), 30.4 (CH₂CH), 34.3 (CH₂CO₂), 41.3 (CH₂N), 50.0

(CHN), 52.7 (OMe), 178.1 (CO₂Me); MS (DCI, NH₃) m/e

189 (MH^þ, 100).

3.14. Acid cleavage the N-Boc protecting group

To a suspension of an N-Boc-amino compound (1 mmol) in

ether (5 mL), a solution of 1 N HCl–ether (3 mL) was

added. The mixture was stirred at room temperature

overnight. The solvent was evaporated to give the diamine

dihydrochloride product. In some cases, a solution of HCl in

EtOAc (prepared from a mixture of EtOAc, EtOH and AcCl

was used.¹⁶

3.12.2. 7,8-Diamino-decanoic acid methyl ester dihydro-

chloride (20⁰c). Catalytic reduction of 18⁰c (90% yield). ¹H

NMR (D₂O) d 1.08 (t, J¼7.5 Hz, 3H, Me), 1.42 (m, 4H,

(CH₂)(CH₂)₂CO₂), 1.77 (m, 6H, CH₂Me, CH₂(CH₂)₂CH₂-

CH₂CO₂), 2.42 (t, J¼7.3 Hz, 2H, CH₂CO₂), 3.70 (m and s,

superimposed, 5H, two CHN and OMe); ¹³C NMR (D₂O)

d 9.7 (Me), 20.6 (CH₂Me), 24.3 (CH₂CH₂CO₂), 24.8

(NCHCH₂CH₂), 28.5 (CH₂(CH₂)₃CO₂), 34.1 (CH₂CO₂),

52.9 (NHCH(CH₂)₂), 179.2 (CO₂Me); MS (DCI, NH₃) m/e

217 (MH^þ, 100), 203 (MH^þ, 87); HRMS (DCI, CH₄) calcd

for C₁₁H₂₅N₂O₂(MH^þ) 217.1916 found 217.1910.

3.14.1. 7,8-Diamino-9-methylsulfanyl-nonanoic acid

methyl ester dihydrochloride (20⁰i). From 5⁰iI by

1

reductive amination and hydrolysis (50% yield). H NMR

(D₂O) d 1.40 (m, 4H, (CH₂)₂(CH₂)₂CO₂), 1.60 (m, 4H,

CH₂(CH₂)₄CO₂), 2.23 (s, 3H, SMe), 2.42 (t, J¼7.4 Hz, 2H,

CH₂CO₂), 2.93 (ABq of d, J_AB¼16 Hz, J_AX¼9.5 Hz,

J_BX¼5.5 Hz, 2H, CH₂S), 3.70 (s, 3H, OMe), 3.80 (m, 2H,

two CH’s). ¹³C NMR (D₂O) d 15.4 (SMe), 24.4 (CH₂CH₂-

CO₂), 24.8 and 24.9 (two CH₂CH₂CHN), 27.4 (CH₂(CH₂)₂-

CO₂), 28.3 and 28.5 (two CH₂CHN), 31.6 and 32.7 (two

CH₂S), 34.0 (CH₂CO₂), 51.4 (OMe), 51.9 and 52.6 (two

CHCH₂S), 52.7 and 52.8 (two CHCHCH₂S), 175.0 (CO₂).

MS (CI/NH₃) m/e 249 (MH^þ22HCl, 100).

3.12.3. 7,8-Diamino-9-methyl-octanoic acid methyl ester

dihydrochloride (20⁰d). Catalytic reduction of 18⁰d (92%

yield). ¹H NMR (D₂O) d 1.10 (m, 3H, CHMe₂), 1.46 (m, 4H,

CH₂(CH₂)₂CH₂CH₂CO₂), 2.17 (m, 1H, CHMe₂), 2.43 (t,

1744

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

3.15. DTB and derivatives—imidazolone formation

rated to dryness and the residue partitioned between 1 N

HCl and EtOAc. The aqueous layer was extracted with

EtOAc (4 times) and the combined organic layers were

washed with 5% NaHCO₃(twice) and brine (once), dried

(MgSO₄), ﬁltered and evaporated to give the desired

cyclized product, as a mixture of two diastereomers.

Method A.²⁴A mixture of a DAPA·2HCl Me ester derivative

(1 mmol) and Et₃N (0.2 g, 2 mmol) in dry CH₂Cl₂(10 mL)

was stirred in an ice bath for 30 min. A solution of CDI

(0.2 g, 1.2 mmol) in dry CH₂Cl₂(5 mL) was added and the

mixture was stirred at room temperature overnight. The

mixture was evaporated and the residue was partitioned

between 1 N HCl and EtOAc. The aqueous layer was

extracted with EtOAc (4£) and the combined organic layers

were washed with 5% NaHCO₃(2£), brine, dried (MgSO₄),

ﬁltered and evaporated to give the product, in the form of

two diastereomers.

3.17. 5-(5-Methyl-2-thioxo-imidazolidin-4-yl)-pentanoic

acid methyl ester (22⁰b)

From 20⁰b, as a viscous yellow oil (84% yield). MS (CI/

NH₃) m/e 245 (MH^þ, 100), 213 (MH^þ2MeOH, 4); HRMS

(CI/CH₄) calcd for C₁₁H₂₁N₂O₂S (MH^þ), 245.13238 found

245.06617.

Method B.²⁵An aqueous solution (10 mL) of NaOH (0.4 g,

10 mmol) and a DAPA·2HCl derivative (1 mmol) was

stirred at room temperature for 10 min. A solution of

triphosgene (0.3 g, 1 mmol) in dioxane (10 mL) was added.

The mixture became hot and the pH dropped from ,10 to

,8. The resulting mixture was stirred at room temperature

for 2 days and was then evaporated. Trituration of the

residue with MeOH, ﬁltration and evaporation afforded the

product. Note: both the free acid and the ester could be used

as substrates. The product was either the pure acid or a

mixture of acid and ester. In the case of a mixture, the

product was dissolved in 4 N HCl and stirred at room

temperature overnight, to afford, after evaporation, the free

acid.

3.17.1. 5-(5-Methyl-2-thioxo-imidazolidin-4-yl)-penta-

noic acid (22b). Hydrolysis of 22⁰b, yellow solid (quanti-

tative yield). H NMR (D₂O) d cis diastereomer 1.33 (m,

1

4H, CH₂CH₂CH₂CH₂CO₂), 1.41 (d, J¼6.5 Hz, 3H, Me),

1.57 (m, 4H, CH₂CH₂CH₂CH₂CH₂CO₂), 2.35 (m, 2H,

CH₂CO₂), 4.12 (m, 1H, CHCH₂), 4.08 (q, J¼6.5 Hz, 1H,

CHMe). trans diastereomer 1.19 (d, J¼6.6 Hz, 3H, Me),

1.33 (m, 4H, CH₂CH₂CH₂CH₂CO₂), 1.57 (m, 4H, CH₂-

CH₂CH₂CH₂CH₂CO₂), 2.35 (m, 2H, CH₂CO₂), 3.72 (m,

1H, CHCH₂), 4.40 (q, J¼6.8 Hz, 1H, CHMe). MS (CI/NH₃)

m/e 231 (MH^þ, 100); HRMS (CI/CH₄) calcd for

C₁₀H₁₉N₂O₂S (MH^þ), 231.11672 found 231.09542; (M^þ),

230.10890 found 230.09407.

3.15.1. 6-(2-Oxo-imidazolidin-4-yl)-hexanoic acid

(21a).²⁶From 20⁰a, method A (97% yield). ¹H NMR

(CD₃OD) d 1.4 (m, 4H, (CH₂)₂(CH₂)₂CO₂), 1.64 (m, 4H,

CH₂(CH₂)₂CH₂CH₂CO₂), 2.32 (m, 2H, CH₂CO₂), 3.07 (m,

1H, CHN), 3.80 (m, 2H, CH₂N); ¹³C NMR (D₂O) d 24.6 and

26.2 (CH₂(CH₂)₂CO₂and CH₂(CH₂)₃CO₂), 29.0 (CH₂CH₂-

CO₂), 35.1 (CH₂CO₂), 38.0 (CH₂(CH₂)₄CO₂), 46.6 (CH₂N),

53.3 (CHN), 163.7 (NCON), 184.1 (CO₂); MS (CI, i-Bu)

m/e 201 (MH^þ, 100); HRMS (DCI, CH₄) calcd for

C₉H₁₇N₂O₂(MH^þ) 201.1239 found 201.1200.

3.17.2. 5-(5-Methylsulfanylmethyl-2-thioxo-imidazolin-

4-yl)-pentanoic acid (22i). From 20⁰I, tan crystals (82%

yield). ¹H NMR (CDCl₃) d 1.38 (m, 4H, CH₂CH₂CH₂CH₂-

CO₂), 1.64 (m, 4H, CH₂CH₂CH₂CH₂CH₂CO₂), 2.14 and

2.15 (two s, 3H, SMe), 2.20 (m, 1H, CH₂S), 2.33 (t, J¼

7.3 Hz, 2H, CH₂CO₂), 2.65 (m, 1H, CH₂S), 3.68 (s, 3H,

OMe), 3.70 (m, 1H, CH), 4.03 (m, 1H, CH), 6.60–6.90

(several m, 2H, two NH’s). ¹³C NMR (CDCl₃) d 15.7 and

15.9 (two SMe), 24.63 and 24.9 (two CH₂CH₂CO₂), 25.8

and 26.2 (two CH₂CH₂CH₂CH₂CO₂), 28.7 and 28.8 (two

CH₂CH₂CH₂CO₂), 29.7 (CH₂CH₂CH₂CH₂CH₂CO₂), 33.8

and 34.0 (two CH₂CO₂), 35.1 and 38.9 (two CH₂S), 51.5

(OMe), 58.4 and 59.9 (two CHCH₂S), 61.7 and 62.6 (two

CHCHCH₂S), 173.9 (CO₂), 182.3 (CS). MS (CI/NH₃) m/e

291 (MH^þ, 100), 259 (MH^þ2MeOH, 4); HRMS (CI/CH₄)

calcd for C₁₂H₂₃N₂O₂S₂(MH^þ), 291.12010 found

291.08042.

3.15.2. 6-(5-Ethyl-2-oxo-imidazolidin-4-yl)-hexanoic

acid (21c).²⁷Cyclization of 20⁰c, method A (97% yield).

¹H NMR (D₂O) d 0.89 (t, J¼7 Hz, 4H, Me), 1.33 (m, 4H,

CH₂CH₂(CH₂)₂CO₂), 1.52 (m, 6H, CH₂(CH₂)₂CH₂CH₂CO₂

and CH₂Me), 2.16 (t, J¼7 Hz, 2H, CH₂CO₂), 3.41 (m, 1H,

CHCH₂Me), 3.73 (m, 2H, CH(CH₂)₅); ¹³C NMR (D₂O)

d 9.1 (Me), 24.6 (CH₂(CH₂)₃CO₂), 26.3 (CH₂CH₂CO₂),

28.4 (CH₂(CH₂)₂CO₂), 29.1 (CH₂CO₂), 35.4 (CH₂Me),

38.1 (CH₂(CH₂)₄CO₂), 58.3 (CH₂CHN), 60.1 (CHN),

165.5 (NCON), 175.2 (CO₂); MS (CI, NH₃) m/e 243

(MH^þ, 42), 211 (MH^þ2MeOH, 31); HRMS (DCI,

CH₄) calcd for C₁₁H₂₁N₂O₂(MH^þ) 229.1552 found

229.1570.

3.17.3. 5-[5-(2-Methylsulfanyl-ethyl)-2-thioxo-imidazoli-

din-4-yl]-pentanoic acid (22g). From 20⁰g, yellow powder

(quantitative yield). ¹H NMR (CDCl₃) d 1.36 (m, 4H,

CH₂CH₂CH₂CH₂CO₂), 1.64 (m, 4H, CH₂CH₂CH₂CH₂CH₂-

CO₂), 1.88 (m, 1H, CH₂CH₂S), 2.11 (s, 3H, SMe), 2.32 (t,

J¼7.3 Hz, 2H, CH₂CO₂), 2.59 (t, J¼7 Hz, 2H, CH₂S), 2.65

(m, 1H, CH₂CH₂S), 3.67 (s, 3H, OMe), 3.75 (m, 1H, CH),

4.03 (m, 1H, CH), 7.00–7.40 (several m, 2H, two NH’s).

¹³C NMR (CDCl₃) d 15.5 (SMe), 24.7 (CH₂CH₂CO₂),

25.0 (CH₂CH₂CH₂CH₂CO₂), 28.8 (CH₂CH₂CH₂CO₂), 28.9

(CH₂CH₂CH₂CH₂CH₂CO₂), 30.3 (CH₂CH₂S), 31.2

(CH₂S), 33.9 (CH₂CO₂), 51.5 (OMe), 59.3 and 60.3 (two

CHCH₂CH₂S), 62.1 and 63.0 (two CHCHCH₂CH₂S), 174.0

(CO₂), 181.8 (CS). MS (CI/NH₃) m/e 305 (MH^þ, 100),

273 (MH^þ2MeOH, 11); HRMS (CI/CH₄) calcd for

C₁₃H₂₅N₂O₂S₂(MH^þ), 305.13575 found 305.07004.

3.16. General procedure for the preparation of

imadizolidinethiones

A mixture of a DAPA·2HCl methyl ester derivative 20⁰

(1 mmol) and Et₃N (0.2 g, 2 mmol) in dry CH₂Cl₂(10 mL)

was stirred at ca. 0 8C for 30 min. A solution of N,N⁰-

thiocarbonyldiimidazole (0.21 g, 1.2 mmol) in dry CH₂Cl₂

(10 mL) was added and the mixture was stirred at room

temperature overnight. The resulting mixture was evapo-

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1745

3.18. General procedure for the preparation of N-Cbz

amino acid methyl ester derivatives

CH₂Ph–CH₂Ph, 2), 305 (MH^þ2CO₂CH₂Ph–OCH₂Ph,

96); HRMS (CI/CH₄) calcd for C₂₈H₃₉N₂O₇S (MH^þ),

547.24780 found 547.23947.

Benzyl chloroformate (0.16 mL, 1.1 mmol) was added

dropwise, during 30 min to an ice-cooled turbid mixture

of the amino acid hydrochloride Me ester (1 mmol) and

NaHCO₃(0.4 g, 5 mmol) in EtOAc (3 mL)/H₂O (2 mL).

The mixture was stirred at room temperature for 3 h and was

then decanted. The organic layer was washed with 1 N HCl

(2£), H₂O (2£), dried (MgSO₄), ﬁltered and evaporated to

give the product.

3.18.4. 10-Methanesulﬁnyl-7,8-bis-methoxycarbonyl-

amino-decanoic acid methyl ester (20⁰hIII). Periodate

oxidation^10eof₀20⁰gIII (93% yield). Note₀: partial NMR

(CDCl₃) d 2.58–2.67 (s, 3H, SMe) compared to 2.10–2.13

(s, 3H, SMe) and 2.79 (m, 2H, CH₂S), as compared to 2.55

and 2.68 (two m, 2H, CH₂S. MS (DCI/NH₃) m/e 412

(MNH₄^þ, 33), 395 (MH^þ, 100), 363 (MH^þ2MeOH, 17);

HRMS (CI/CH₄) calcd for C₁₆H₃₁N₂O₇S (MH^þ),

395.18520 found 395.17896.

1

spectrum of 20 hIII compared to that of 20 gIII. H NMR

3.18.1. 7,8-Bis-benzyloxycarbonylamino-10-methylsulfa-

nyl-decanoic acid methyl ester (20⁰gII). Compound 20⁰gII

was obtained as a viscous oil from 20⁰g (63% yield). Note:

two equivalents of benzyl chloroformate were used. ¹H

NMR (CDCl₃) d 1.33 (m, 4H, CH₂CH₂CH₂CH₂CO₂), 1.60

(m, 4H, CH₂(CH₂)₂CH₂CO), 1.75 (m, 2H, CH₂CH₂S), 2.07

(s, 3H, SMe), 2.28 (t, J¼7.2 Hz, 2H, CH₂CO₂), 2.54 (m, 2H,

CH₂S), 3.66 (s, 3H, OMe), 3.78 (m, 2H, two CH’s), 4.70–

5.00 (several m, 2H, two NH’s), 5.08 (two s, 4H, CH₂Ar),

7.32 (two m, 10H, Ar). MS (CI/NH₃) m/e 548 (MNH₄^þ, 67),

531 (MH^þ, 100), 456 (MNH₄^þ2CH₂Ph, 5), 440 (MH^þ2

CH₂Ph, 4), 397 (MH^þ2CO₂CH₂Ph, 12); HRMS (CI/CH₄)

calcd for C₂₈H₃₉N₂O₆S (MH^þ), 531.25228 found

531.25697.

3.19. Pyrolysis of sulfoxides to vinyl derivatives

Method A.^10aA mixture of the sulfoxide (1 mmol) and

CaCO₃(0.4 g, 4 mmol) in o-dichlorobenzene (5 mL) was

stirred at room temperature for 1 h. The mixture was

transferred to a pre-heated oil bath (ca. 174 8C). The

pyrolysis was monitored by tlc (hexane/EtOAc 4:1,

spraying with phosphomolybdic acid). The reaction was

complete after 2 h and the product was obtained by in very

poor yield ﬂash chromatography.

Method B.^10bThe sulfoxide were distilled in a Kugelrohr

apparatus at elevated temperatures (.200 8C) and high

vacuum, and were usually obtained as oils that solidiﬁed at

room temperature. Substrates containing labile Boc groups,

or acidic hydrogens (e.g. b-keto esters) could not be

pyrolyzed, due to decomposition of the substrate and

product. Method B was usually followed, due to better yield.

3.18.2. 7,8-Bis-methoxycarbonylamino-10-methylsulfa-

nyl-decanoic acid methyl ester (20⁰gIII). From 20⁰g.

Et₃N (0.2 g, 2 mmol) was added to a suspension of 20⁰g

(0.26 g, 1 mmol) in dry CH₂Cl₂(5 mL). The mixture was

stirred vigorously until it became homogenous and was

further stirred at room temperature for 10 min. Dimethyl

dicarbonate (0.26 g, 2 mmol) was added and the mixture

was stirred at room temperature for 3.5 h. The resulting

mixture was evaporated to dryness and the residue was

partitioned between 1 N HCl and EtOAc. The aqueous layer

was extracted with EtOAc (4£) and the combined organic

layers were dried (MgSO₄), ﬁltered and evaporated to give

20⁰gIII (98% yield). ¹H NMR (CDCl₃) d 1.35 (m, 4H,

CH(CH₂)₂(CH₂)₂CO₂), 1.63 (m, 4H, CHCH₂(CH₂)₂CH₂),

2.11 (m, 1H, CH₂CH₂S), 2.10–2.12 (several s, 3H, SMe),

2.29 (m, 1H, CH₂CH₂S), 2.27 and 2.30 (two t, J¼7.5, 7 Hz,

2H, CH₂CO₂), 2.55 (m, 1H, CH₂S), 2.68 (t, J¼6.9 Hz, 1H,

CH₂S), 3.65–3.76 (several s, 9H, CH₂CO₂Me and two

NCO₂Me), 3.75–4.02 (several m, 2H, two CH’s), 4.70–

5.25 (several m, 2H, two NH’s). MS (CI/NH₃) m/e 396

(MNH₄^þ, 86), 379 (MH^þ, 100), 364 (MH^þ2MeOH, 10),

347 (MH^þ2two MeOH, 45).

3.19.1. 8-Acetylamino-7-oxo-dec-8-enoic acid methyl

ester (23⁰IV). Undesired isomer obtained as from 5⁰hIV

when pyrolyzed at 220 8C and 1 Torr (70% yield). ¹H NMR

(CDCl₃) d1.34 (m, 2H, CH₂CH₂CH₂CO₂), 1.64 (m, 4H,

CH₂CH₂CH₂CH₂CO₂), 1.85 (d, J¼7.1 Hz, 3H, MeCH),

2.14 (s, 3H, MeCO), 2.32 (t, J¼7.4 Hz, 2H, CH₂CO₂), 2.70

(dd, J¼8, 6.7 Hz, 2H, CHCOCH₂), 3.67 (s, 3H, OMe), 6.67

(q, J¼7.1 Hz, 1H, CH), 7.25 (brs, 1H, NH). ¹³C NMR

(CDCl₃) d15.6 (MeCH), 24.2 (MeCO), 24.7 (CH₂CH₂CO₂),

25.0 (CH₂(CH₂)₂CO₂), 28.7 (CH₂CH₂CH₂CO₂), 33.8

(CH₂CO₂), 36.3 (CH₂COCH), 132.6 (CH), 134.5 (CNH),

173.7 (CON), 174.0 (CO₂), 197.4 (CH₂COCH). MS (EI)

m/e 255 (M^þ, 18), 224 (M^þ2MeOH, 2), 213 (M^þ2

MeCO₂, 100), 196 (M^þ2C₂H₄O₂, 4), 182 (M^þ2MeOH–

MeCO₂, 48), 153 (M^þ2MeCO₂–C₂H₄O₂, 20).

3.18.3. 7,8-Bis-benzyloxycarbonylamino-10-methanesul-

ﬁnyl-decanoic acid methyl ester (20⁰hII). Periodate

oxidation^10eof 20⁰gII (93% yield). Notes: (a) due to the

insolubility of 20⁰gII in MeOH and H₂O, the starting

material was suspended in MeOH, while CH₂Cl₂was added

until complete dissolution and only then was the aqueous

solution of NaIO₄added (b) partial NMR spectrum of 20⁰hII

compared to that of 20⁰gII. ¹H NMR (CDCl₃) d 2.49 (s, 3H,

SMe) compared to 2.07 (s, 3H, SMe), and 2.71 (m, 2H,

CH₂S) compared to 2.54 (m, 2H, CH₂S). MS (DCI/NH₃)

m/e 564 (MNH₄^þ, 29), 547 (MH^þ, 100), 456 (MH^þ2CH₂Ph,

12), 439 (MH^þ2OCH₂Ph, 61), 412 (MH^þ2CO₂CH₂Ph,

13), 395 (MH^þ2CO₂CH₂Ph–O, 44), 321 (MH^þ2CO₂-

3.19.2. 7,8-Bis-methoxycarbonylamino-dec-9-enoic acid

methyl ester (20⁰oIII). From 20⁰hIII, at 240 8C and 2 Torr

(41% yield). H NMR (CDCl₃) d 1.35 (m, 4H, (CH₂)₂-

1

(CH₂)₂CO₂), 1.62 (m, 4H, CH₂(CH₂)₂CH₂CH₂CO), 2.32

(m, 2H, CH₂CO₂), 3.41 and 3.68 (two m, 1H, NCHCH₂),

3.67 (s, 9H, three OMe’s), 3.68 and 4.21 (two m, 1H,

CHCHCHCH₂CH₂), 4.50–5.00 (several m, 2H, two NH’s),

5.22 and 5.30 (two m, 2H, CH₂vCH), 5.80 (m, 1H,

CH₂vCH). ¹³C NMR (CDCl₃) d 23.0–35.0 (chain CH₂’s),

51.5 (CH₂CO₂Me), 52.3 and 53.4 (two NCO₂Me), 56.3 and

57.2 (two¼CHCH), 59.0 and 61.7 (two NCHCH₂), 117.4

and 118.4 (two¼CH), 134.1 and 137.3 (two CH₂CHN),

þ

155.0 (CON), 174.0 (CO₂). MS (CI/NH₃) m/e 348 (MNH₄

,

1746

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

100), 331 (MH^þ, 96), 316 (MNH^þ₄2MeOH, 16), 299

(MH^þ2MeOH, 41).

8-Amino-7-oxo-decanoic acid hydrochloride (4c).

8-Amino-10-methylsulfanyl-7-oxo-decanoic acid hydro-

chloride (4g).

Note: experimental procedures for the following com-

pounds may be obtained directly from the corresponding

authors.

8-Amino-10-methanesulﬁnyl-7-oxo-decanoic acid hydro-

chloride (4h).

4-[(tert-Butyloxycarbonyl)amino]-5-(methylthio)-3-oxo-

pentanoic acid methyl ester (2⁰iI).

8-Amino-9-methylsulfanyl-7-oxo-nonanoic acid hydro-

chloride (4i).

4-[(tert-Butyloxycarbonyl)amino]-5-(tert-butyloxycarbo-

nyl)thio]-3-oxopentanoic acid methyl ester (2⁰kI).

8-Amino-9-mercapto-7-oxo-nonanoic acid hydrochloride (4j).

4-Benzyloxycarbonylamino-5-benzyloxycarbonylsulfanyl-

3-oxo-pentanoic acid methyl ester (2⁰lII).

8-Amino-9-hydroxy-7-oxo-nonanoic acid hydrochloride

(4p).

5-Benzylsulfanyl-4-tert-butoxycarbonylamino-3-oxo-pen-

tanoic acid methyl ester (2⁰mI).

8-Amino-9-hydroxy-7-oxo-decanenitrile hydrochloride

(14r).

4-Acetylamino-5-acetylsulfanyl-3-oxo-pentanoic acid

methyl ester (2⁰nIV).

8-Amino-9-hydroxy-7-oxo-nonanoic acid methyl ester

hydrochloride (5⁰p).

4-tert-Butoxycarbonylamino-3-oxo-5-(tetrahydro-pyran-2-

yloxy)-pentanoic acid methyl ester (2⁰qI).

8-Amino-9-hydroxy-7-oxo-decanoic acid methyl ester

hydrochloride (5⁰r).

4-tert-Butoxycarbonylamino-3-oxo-5-(tetrahydro-pyran-2-

yloxy)-hexanoic acid methyl ester (2⁰sI).

8-Amino-10-methylsulfanyl-7-oxo-decanoic acid methyl

ester hydrochloride (5⁰g).

4-Methoxycarbonylacetyl-oxazolidine-3-carboxylic acid

tert-butyl ester (16⁰p).

8-Amino-9-methylsulfanyl-7-oxo-nonanoic acid methyl

ester hydrochloride (5⁰I).

4-Methoxycarbonylacetyl-5-methyl-oxazolidine-3-carb-

oxylic acid tert-butyl ester (16⁰r).

8-Amino-9-mercapto-7-oxo-nonanoic acid methyl ester

hydrochloride (5⁰j).

2-(2-tert-Butoxycarbonylamino-propionyl)-heptanedioic

acid 7-ethyl ester 1-methyl ester (3⁰bI).

8-tert-Butoxycarbonylamino-7-oxo-octanoic acid methyl

ester (5⁰aI).

2-(2-tert-Butoxycarbonylamino-butyryl)-heptanedioic acid

7-ethyl ester 1-methyl ester (3⁰cI).

8-(tert-Butoxycarbonylamino)-9-hydroxy-7-oxo-decanoic

acid methyl ester (5⁰qI).

2-(2-tert-Butoxycarbonylamino-3-methyl-butyryl)-hep-

tanedioic acid 7-ethyl ester 1 methyl ester (3⁰dI).

8-tert-Butoxycarbonylamino-10-methylsulfanyl-7-oxo-

decanoic acid methyl ester (5⁰gI).

2-(2-tert-Butoxycarbonylamino-4-methyl-pentanoyl)-hep-

tanedioic acid 7-ethyl ester 1-methyl ester (3⁰eI).

8-tert-Butoxycarbonylamino-10-methanesulﬁnyl-7-oxo-

decanoic acid methyl ester (5⁰hI).

2-(2-tert-Butoxycarbonylamino-3-methyl-pentanoyl)-hep-

tanedioic acid 7-ethyl ester 1-methyl ester (3⁰fI).

8-tert-Butoxycarbonylamino-9-methylsulfanyl-7-oxo-non-

anoic acid methyl ester (5⁰iI).

2-(2-tert-Butoxycarbonylamino-4-methylsulfanyl-butyryl)-

heptanedioic acid 7-ethyl ester 1-methyl ester (3⁰gI).

8-Amino-7-hydroxyimino-octanoic acid methyl ester

hydrochloride (18⁰a).

2-(2-tert-Butoxycarbonylamino-4-methanesulﬁnyl-butyr-

yl)-heptanedioic acid 7-ethyl ester 1-methyl ester (3⁰hI).

8-Amino-7-hydroxyimino-octanoic acid hydrochloride

(18c).

Ethyl 8-[(tert-butyloxycarbonyl)amino]-6-(methoxycarbo-

nyl)-9-(methylthio)-7-oxononanoate (3⁰iI).

8-Amino-9-methyl-7-hydroxyimino-decanoic acid hydro-

chloride (18d).

2-(3-tert-Butoxycarbonyl-oxazolidine-4-carbonyl)-hep-

tanedioic acid 7-ethyl ester 1-methyl ester (17⁰p).

8-Amino-7-hydroxyimino-9-methyl-undecanoic acid hydro-

chloride (18f).

2-(3-tert-Butoxycarbonyl-5-methyl-oxazolidine-4-carbo-

nyl)-heptanedioic acid 7-ethyl ester 1-methyl ester (17⁰r).

8-Amino-7-hydroxyimino-9-mercapto-nonanoic acid hydro-

chloride (18j).

A. Nudelman et al. / Tetrahedron 60 (2004) 1731–1748

1747

5. (a) Bui, B. T. S.; Florentin, D.; Fournier, F.; Ploux, O.;

8-Amino-7-hydroxyimino-9-mercapto-nonanoic

methyl ester hydrochloride (18⁰j).

acid

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6-(5-Methylsulfanylmethyl-2-oxo-imidazolidin-4-yl)-hexa-

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6-[5-(2-Methanesulﬁnyl-ethyl)-2-oxo-imidazolidin-4-yl]-

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Generous support for this work by the ‘Marcus Center for

Pharmaceutical and Medicinal Chemistry’ and the ‘Bronia

and Samuel Hacker Fund for Scientiﬁc Instrumentation’ at

Bar Ilan University, are gratefully acknowledged.

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