Design, synthesis and evaluation of imidazolylmethyl carbamate prodrugs of alkylating agents

TETRAHEDRON

Pergamon

Tetrahedron 56 (2000) 645–657

Design, Synthesis and Evaluation of Imidazolylmethyl Carbamate

Prodrugs of Alkylating Agents

*

Michael P. Hay, William R. Wilson and William A. Denny

Auckland Cancer Society Research Centre, School of Medical and Health Sciences, The University of Auckland,

Private Bag 92019, Auckland, New Zealand

Received 8 October 1999; revised 5 November 1999; accepted 18 November 1999

Abstract—Two approaches to prodrugs of alkylating agents based on an imidazolylmethyl carbamate nucleus were explored. A 2-azido

analogue (3) of the bis-carbamate carmethizole (1) displayed similar aerobic cytotoxicity to 1 in a panel of human and murine cell lines.

Approaches to the 2-amino and 2-carbamoyl analogues are described. In the second approach an imidazolylmethanol was used as a ‘trigger’

linked via a carbamate to the alkylating agent N,N-bis(2-chlorethyl)amine (BCEA). Nitroimidazole and methylsulphinylimidazole carbamate

prodrugs 6–8 were 5–20-fold less toxic than BCEA. Despite this deactivation in the prodrug form, little increase in cytotoxicity was

observed under hypoxia. The data suggest that BCEA released on bioreduction is not sufﬁciently potent to contribute signiﬁcant additional

Most current cancer chemotherapeutic agents are cytotoxins

with primary selectivity against dividing cells rather than

cancer cells. In the search for new cancer therapeutics, there

is an increasing interest in improving the tumour-selectivity

of such cytotoxins by masking them as prodrugs, which may

be activated in a tumour-speciﬁc manner.^1–3Strategies to

this end include antibody-directed enzyme prodrug therapy

(ADEPT),^4–6gene-directed enzyme prodrug therapy

(GDEPT),^7,8and the use of tumour hypoxia to facilitate

bioreductive activation.^9,10The presence of hypoxia within

solid tumours¹¹is a major factor contributing to their

radioresistance.^12–14It is also a signiﬁcant physiological

difference between solid tumours and normal tissue, provi-

ding an opportunity for tumour-selective activation of bio-

reductive prodrugs.¹⁵A requirement for such prodrugs is

that they undergo initial reduction by endogenous enzymes

to an oxygen-reversible one-electron adduct to provide a

cytotoxic species.⁹

suggested to be a consequence of the ability of the 2-sub-

stituent to stabilise the transition state of the S_N1-type acti-

vation of the hydroxymethyl groups, which eventually leads

to DNA alkylation.¹⁹These reports led us to consider the

hydroxymethylimidazole nucleus as a potentially useful

moiety around which to design prodrugs of alkylating

agents for bioreductive activation in tumours. We explored

two strategies in the development of such prodrugs.

In the ﬁrst approach,²⁰we aimed to use the bis-hydroxy-

methylimidazole nucleus derived from carmethizole as the

alkylating unit, with 2-nitrogen substituents to deactivate

the alkylating groups. While the 2-amino derivative (2) is

expected to be more reactive than carmethizole (1) on the

basis of its electron-donating properties [s_p(NH₂)Ϫ0.66,

s_p(SMe)0.00]²¹a 2-azido derivative 3 or a 2-carbamoyl

derivative 4 contain considerably less electron-donating

substituents [s_p(N₃)0.15, s_p(NHCO₂Me)Ϫ0.15],²²and

might therefore provide prodrug forms of 2. The use of the

azido group as a masked amine function is well known,²³

and metabolism of aryl azides to amines has been demon-

strated.^24–26Hence we targeted the 2-azido (3) and 2-carba-

moyl analogues (4) of carmethizole (1) as examples of this

class of prodrug.

In the course of our studies into bioreductive prodrugs our

attention was drawn to carmethizole (1), a novel bis-carba-

mate alkylating agent,¹⁶which forms DNA–protein and

DNA–DNA cross-links in vitro,¹⁷and has antitumour

activity against murine leukaemias, solid tumours and

human tumour xenografts in vivo.^16,18The antitumour

activity of related bis-hydroxymethylimidazole carbamates

was found to be enhanced by electron-donating 2-sub-

stituents, while electron-withdrawing 2-substituents led to

compounds that were inactive.¹⁶This relationship was

Keywords: antitumour compounds; carbamates; imidazoles/imidazolines.

* Corresponding author.

PII: S0040-4020(99)01031-5

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M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

Scheme 1. Reductive activation of 2-nitroimidazole-5-methylcarbamates.

Our second strategy aimed to use a substituted hydroxy-

methylimidazole ring as the ‘trigger’ unit rather than as

the alkylating unit. In this concept, reduction of the trigger

unit leads to activation of a separate alkylating moiety,

which is attached via a deactivating carbamoyl linker. Bio-

reduction of an electron-withdrawing substituent on the

imidazole ring to a more electron donating moiety would

activate the carbamate unit to nucleophilic attack, with

subsequent fragmentation of the resulting carbamic acid,

releasing a secondary amine as the cytotoxic ‘effector’

(Scheme 1). In the present study, the nitrogen mustard

N,N-bis(2-chloroethyl)amine (BCEA), was selected as the

alkylating agent. Nitrogen mustards are signiﬁcantly deac-

tivated by electron withdrawing substituents,²⁷with mustard

N-carbamates thus expected to be considerably less toxic

than the free mustard.

Synthesis of nitrogen analogues of carmethizole (1) was

accomplished using synthetic approach outlined

a

previously in a preliminary account (Scheme 2).²⁰Thus

imidazole-4,5-dicarboxylic acid was esteriﬁed and N-alkyl-

ated to give the diester 9 (47% for 2 steps), which was

reduced to the diol 10 with LiAlH₄(66%), and protected as

the di-TBDMS ether 11 (74%). Lithiation and reaction with

tosyl azide³⁶(Caution) gave the azide 12 in 69% yield.

Deprotection of the silyl ether groups with TBAF gave 13

(70%) and reaction with methyl isocyanate in the presence

of catalytic dibutyltin diacetate gave the azide analogue 3 in

86% yield. Repeated attempts to reduce azide 3 to the corre-

sponding amine 2 by catalytic hydrogenation using Pd/C,

Pt/C, or Lindlar catalyst were unsuccessful, with rapid

decomposition observed in all cases. Milder reduction

conditions using Staudinger conditions³⁷or PPh₃were

also unsuccessful, highlighting the inherent reactivity of

imidazole 4,5-bis(methylcarbamates) with strongly

electron-donating substituents at the 2-position.

Nitro and sulphoxide substituents were selected as suitable

electron-withdrawing substituents to place in conjugation to

the methyl carbamate. Nitro groups are well documented as

undergoing bioreduction under hypoxic conditions¹⁵and

provide

a

large change in electron density

[s_p(NO₂)0.78, s_p(NH₂)Ϫ0.66].²¹Precedent for the

reductive elimination of 5-nitroimidazole carbamates exists

in the mechanism of ronidazole²⁸and examples of 5-nitro-

imidazole carbamates have been prepared.^3,29A recent

report demonstrated the fragmentation of analogous

2-nitroimidazolyl esters upon radiolytic reduction.³⁰The

fragmentation of a 4-nitro-5-methylimidazole quaternary

salt of mechlorethamine by radiolytic reduction has also

been recently reported.^31,32

Analogous to the carmethizole analogues,¹⁹we expected a

2-sulphoxide group to deactivate the carbamate to displace-

ment [s_p(S(O)Me)0.49, s_p(SMe)0.00].²¹Bioreduction

of sulphoxides has been observed for a number of sulph-

oxide drugs,³³most notably sulindac, a non-steroidal

anti-inﬂammatory agent.^34,35

In another attempt to prepare carbamate derivative 4, the

azide 12 was reduced by catalytic hydrogenation to give

amine 14 (91%) (Scheme 3). Reaction with trityl chloride

gave the protected aminoimidazole 15 (93%), which was

deprotected to give diol 16 in 77% yield. Reaction of diol

Scheme 2. Reagents: (i) SOCl₂, DMF, EtOH; (ii) K₂CO₃, MeI, DMF; (iii) LiAlH₄, THF; (iv) TBDMSCl, imidazole, DMF; (v) n-BuLi, tosylazide, THF; (vi)

TBAF, THF; (vii) MeNCO, n-Bu₂Sn(OAc)₂, DCM.

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

647

Scheme 3. Reagents: (i) H₂, Pd/C, EtOH; (ii) Ph₃CCl, Et₃N, DCM; TBAF, THF; (iv) MeNCO, n-Bu₂Sn(OAc)₂DCM; (v) (t-BuOCO)₂O, DCM;

(vi) (t-BuOCO)₂O, DMAP, DCM; (vii) TBAF, THF; (viii) HF pyridine, THF; (ix) MeNCO, n-Bu₂Sn(OAc)₂, DCM.

16 with methyl isocyanate and dibutyltin diacetate did not

give the bis-carbamate 17, but rather preferential reaction on

nitrogen to give 18 (14%) and 19 (49%), as well as the

starting material (17%). In an effort to deactivate the

2-amino group we elected to use the BOC protecting

group. Reaction of amine 14 with di-tert-butyl dicarbonate

in DCM gave mixtures of carbamate 20 (57%) and bis-car-

bamate 22 (22%), while addition of DMAP to the reaction

gave clean conversion to bis-carbamate 22 (64%). Depro-

tection of 20 with TBAF gave the diol 21 (90%), which

when reacted with MeNCO and dibutyltin diacetate gave

a mixture of products rather than 4. NMR analysis showed

preferential acylation of the 2-carbamate over reaction at the

4-CH₂OH position. Attempts to deprotect the silyl groups of

22 with TBAF in THF, or KF in acetonitrile were unsuc-

cessful. However, reaction of the bis-carbamate 22 with

HF.pyridine gave the diol 23 in 81% yield, which was

treated with MeNCO and dibutyltin diacetate to give

imidodicarbamate 24 in 95% yield. Attempts to selectively

remove the BOC groups using triﬂuoroacetic acid were not

successful.

Synthesis of carbamate 5 required imidazole ring formation.

Treatment of sarcosine ethyl ester hydrochloride³⁸25 with

sodium formate in formic acid gave the N-formyl sarcosine

derivative in 79% yield (Scheme 4). Formation of the

C-formyl intermediate and ring formation with KSCN

gave the 2-thioimidazole 26 (27%), which was methylated

and transesteriﬁed to give 27 (96%). Reduction of ester 27

with Superhydride^᭨(94%) and oxidation of sulphide 28

with MCPBA gave the 2-sulphinylimidazole methanol 29

in 98% yield. Formation of the carbonate 30 (48%) and

displacement with bis-(2-chloroethyl)amine gave carbamate

5 in 52% yield.

Scheme 4. Reagents: (i) HCO₂Na, HCO₂H; (ii) Ac₂O; (iii) NaOEt, HCO₂Et; (iv) KSCN; (v) K₂CO₃, MeI, DMF; (vi) Superhydride^᭨, THF; (vii) MCPBA,

DCM; (viii) NO₂C₆H₄OCOCl, pyridine, THF; (ix) (ClCH₂CH₂)₂NH·HCl, pyridine.

648

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

Scheme 5. Reagents: (i) NaOH, H₂O; (ii) NaBH₄, EtOH; (iii) NO₂C₆H₄OCOCl, pyridine, THF; (iv) (ClCH₂CH₂)NH.HCl, pyridine.

The readily available ethyl 2-nitroimidazol-5-ylcarboxylate³⁹

(31) was hydrolysed under mild basic conditions to give the

acid 32 quantitatively (Scheme 5). 2-Nitroimidazol-5-

ylmethanol (33) was prepared by sodium borohydride

reduction of the imidazolide⁴⁰of the acid 32 in 68% yield.

This represents a major improvement upon the literature

procedure,³⁹which used lithium borohydride reduction of

the ester 31 to give 33 directly. In our hands, this procedure

gave complex mixtures requiring tedious chromatography

and gave poor yields (typically 5–10%) of the alcohol 33.

Activation of the alcohol 33 as the carbonate 34 (84%) and

displacement with N,N-bis(2-chloroethyl)amine gave 6 in

74% yield.

at the 5-position and reaction with methyldisulphide gave

methyl sulphide 38 (51%), which was oxidised to the sulph-

oxide 39 with MCPBA in 90% yield. Activation of 39 as the

carbonate 40 (81%) and displacement with N,N-bis(2-

chloroethyl)amine gave the carbamate 7 in 80% yield.

Reaction of N-methyl 5-nitroimidazole⁴²41 with para-

formaldehyde gave the alcohol 42 in 57% yield (Scheme

7). Activation of 42 as the carbonate 43 and displacement

with N,N-bis(2-chloroethyl)amine gave the carbamate 8⁴³in

95% yield.

The cytotoxicities of the bis-hydroxymethylimidazoles 1

and 3 were determined under aerobic conditions against a

panel of three cell lines (the Chinese hamster lines AA8 and

UV4, and the murine mammary carcinoma EMT6) using a

growth inhibition assay, which has been described in detail

previously.⁴⁴The UV4 cell line, a nucleotide excision repair

(NER)-defective ERCC-1 mutant derived from AA8, is

hypersensitive to agents whose cytotoxicity is due to

bulky DNA adducts or cross-links,⁴⁵and hence provides

information on the mechanisms of cytotoxicity. Cells in

log-phase growth were exposed to drug for 4 h in 96 well

plates under aerobic conditions, and subsequent cell growth

was measured after 72 h. IC₅₀values were calculated in each

case (Table 1).

Synthesis of 5-sulphoxide-2-carbamate 7 was achieved

using sequential lithiation reactions.⁴¹Lithiation at the

2-position of N-methylimidazole 35 and reaction with

DMF gave aldehyde 36 (80%), which was reduced to the

alcohol 37 with LiAlH₄in 90% yield (Scheme 6). Lithiation

Carmethizole 1 showed an IC₅₀value of 178 mM against

AA8 cells, and was 36-fold more toxic to UV4 cells in

Table 1. In vitro cytotoxicity of bis-hydroxylmethylimidazole prodrugs

Compound

Cytotoxicity (IC₅₀)^a

AA8

UV4

HF^b

EMT6

1

3

178^34^c

189^7

4.7^0.7

15.2^0.7

36^7

12^1

73^12

139^12

^aConcentration (mM) for 50% inhibition of cell proliferation following

4 h exposure under aerobic conditions.

Scheme 6. Reagents: (i) n-BuLi, DMF, THF; (ii) LiAlH₄, THF; (iii)

n-BuLi, t-BuLi, Me₂S₂, THF; (iv) MCPBA, DCM; (v) NO₂C₆H₄OCOCl,

pyridine, THF; (vi) (ClCH₂CH₂)₂NH·HCl, pyridine.

^bHypersensitivity FactorIC₅₀AA8/IC₅₀UV4.

^cValues are mean^SEM for replicate experiments.

Scheme 7. Reagents: (i) (CHO)_n, DMSO; (ii) NO₂C₆H₄OCOCl, pyridine, THF; (ClCH₂CH₂)₂NH·HCl, pyridine.

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

649

Table 2. In vitro cytotoxicity of imidazolecarbamate mustard prodrugs

Table 3. Cytotoxicity of imidazole carbamate mustard prodrugs against

plateau phase cells under aerobic and anoxic conditions, determined by

clonogenic assay of continuously stirred and gassed cell suspensions

Compound

Cytotoxicity (IC₅₀)^a

HF^b

EMT6

a

Compound Cell line CT₁₀, air (mM-h) CT₁₀, N₂(mM-h) HCR^b

AA8

UV4

5

6

7

8

2290^70^c

590^70

2130^190

1000^60

110^30

470^30

153^12

520^90

450^40

6.1^2.0

4.9^0.2

4.4^0.9

3.8^1.1

2.6^0.2

36^6

2170^170

500^8

1070^170

740^100

46^7

BCEA

AA8

UV4^d

UV5^e

AA8

UV4

AA8

0.88

0.66^0.01^c

0.044^0.008

0.72^0.03

4.4

1.4^0.3

1.1^0.2

6.3

1.3

0.068^0.011

0.83^0.06

4.1^0.1

1.5^0.1

1.2^0.1

0.93

Ͼ1.8

Ͼ2.3

1.1

5

6

Ͼ2.5^f

BCEA

Ͼ2.5^f

7.2

^aConcentration (mM) for 50% inhibition of cell proliferation following

18 h exposure under aerobic conditions.

7

8

17.6

10.4

1.7

^bHypersensitivity factorIC₅₀AA8/IC₅₀UV4.

^cValues are mean^SEM for replicate experiments.

^aConcentration×time required to reduce cell survival to 10% of controls.

^bHypoxic cytotoxicity ratioCT₁₀, air/CT₁₀, N₂.

^cErrors are range or SEM for 2–4 separate experiments.

^dERCC1 mutant derived from AA8.

vitro (HF of 36). This is in close agreement with previous

results¹⁷(HF_(AA8/UV4)37) and is consistent with formation

of DNA cross-links being the major mechanism of cyto-

toxicity. Azide 3 shows similar potency against AA8 and

EMT6 cells and an HF of 12, also consistent with DNA

cross-linking and/or the formation of bulky DNA adducts.

Compounds 1 and 3 were also evaluated against a panel of

human tumour cell lines (MGH-U1 bladder carcinoma,

SKOV3 ovarian carcinoma, BE and HT29 colon carcinoma;

data not shown). The IC₅₀values for 4 h exposure to 1

ranged from 76–160 mM, compared to 190–280 mM for

the 2-azido analogue 3. The latter was no more than 2.9-

fold less potent than 1 in any of the human (or rodent) cell

lines. This differential was not considered sufﬁcient to

warrant further investigation of the azido derivative as a

prodrug.

^eERCC2 mutant derived from AA8.

^fNon-toxic at solubility limit (0.5 mM) for 5 h under aerobic conditions.

hypersensitivity relative to the parental AA8 line. The

differential sensitivity of UV4 relative to both UV5 and

AA8 conﬁrms that cytotoxicity of BCEA is due to DNA

crosslinks. As in the IC₅₀assay, the imidazolecarbamate

mustards 5–8 were all considerably less toxic (4.7–20-

fold) than BCEA towards aerobic AA8 cells in the clono-

genic assay. However, little hypoxic selectivity was evident

in these potential bioreductive prodrugs; with the exception

of 6, hypoxic cytotoxicity ratios (HCR) were in the range

0.93–1.7 and were little different than that for BCEA itself

(HCR 1.3). In the case of the 2-nitroimidazole 6, cell killing

could be detected under anoxic but not aerobic conditions at

the solubility limit (0.5 mM) for 5 h, with an HCR of Ͼ1.8.

However, UV4 cells were not signiﬁcantly more sensitive to

6 than were AA8 cells under anoxia. This clearly indicates

that the hypoxic cytotoxicity of 6 is not due to bioreductive

release of BCEA, or to any other DNA crosslinking metabo-

lite. Given the modest cytotoxic potency of BCEA, it is

probable that the hypoxic cytotoxicity of 6 is due to reactive

intermediates derived from reduction of the nitro group

itself, as for simple (non-alkylating) 2-nitroimidazoles

such as misonidazole.^47,48

Aerobic cytotoxicity, measured as IC₅₀values, was also

determined for the four imidazolecarbamate mustard

prodrugs (the 2-methylsulphinylimidazole 5, the 5-isomer

7, and the 2- and 5-nitroimidazoles 6 and 8) and for the

expected alkylating product BCEA using 18 h drug

exposures (Table 2). BCEA showed only modest cytotoxic

potency, with IC₅₀values in the range 46–110 mM in the

repair-competent rodent cells, and 104–214 mM in the

above panel of human tumour cell lines (data not shown).

The HF ratio for BCEA was 36. All the carbamate prodrugs

were less cytotoxic than BCEA (20 fold for 5, 19 fold for 7,

5-fold for 6 and 9-fold for 8 against AA8 cells, with even

higher differentials for the other cell lines), showing that

formation of these carbamates does deactivate the mustard

effectively. All of these compounds showed low HF values

(2–5), suggesting that they are sufﬁciently deactivated to

suppress DNA alkylation.

In conclusion, synthetic difﬁculties precluded the use of

2-carbamates as prodrugs of amino analogues of carmethi-

zole itself. However, the above data suggest that methyl-

sulphinyl- and nitro-substituted imidazole carbamates might

have potential as trigger units for release of secondary

amine cytotoxins from prodrugs, although further develop-

ment of this concept will require release of cytotoxic effec-

tors more potent than the nitrogen mustard BCEA. In an

extension of this approach we have recently reported that

an analogue of 6 in which reduction of a 2-nitroimidazol-5-

ylmethyl carbamate releases a potent amino-seco-CBI-TMI

cytotoxic effector, and that this has promise both as a

hypoxia-selective cytotoxin and as a substrate for nitro-

reductase-mediated GDEPT.⁴⁹

Given these large differentials between the imidazolecarba-

mates and BCEA, the possibility of activation of these

potential prodrugs by endogenous mammalian reductases

under anoxic conditions was assessed. Cytotoxic potency

was evaluated against plateau-phase AA8 cells, using a

clonogenic assay, with potency quantiﬁed as the concen-

tration×time to reduce survival to 10% of controls (CT₁₀;

Table 3). For BCEA, the aerobic CT₁₀was 0.88 mM-h for

AA8 cells, with a 13-fold greater sensitivity for the ERCC1

mutant UV4, which is hypersensitive to bulky DNA mono-

adducts and crosslinks.^45,46In contrast, the ERCC2 mutant

UV5, which is defective in NER of bulky DNA mono-

adducts but not crosslinks,^45,46showed no signiﬁcant

Experimental

General procedures

Analyses were carried out in the Microchemical Laboratory,

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M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

University of Otago, Dunedin, New Zealand. Melting points

were determined on an Electrothermal 2300 melting point

apparatus. IR spectra were recorded on a Midac FT-IR as

KBr discs, unless otherwise stated. NMR spectra were

obtained on a Bruker AM-400 spectrometer at 400 MHz

for ¹H and 100 MHz for ¹³C spectra. Spectra were obtained

in CDCl₃unless otherwise speciﬁed, and are referenced to

Me₄Si. Chemical shifts and coupling constants were

recorded in units of ppm and Hz, respectively. Mass spectra

were determined on a VG-70SE mass spectrometer using an

ionising potential of 70 eV at a nominal resolution of 1000.

High resolution spectra were obtained at nominal reso-

lutions of 3000, 5000 or 10 000 as appropriate. All spectra

were obtained as electron impact (EI) using PFK as the

reference unless otherwise stated. Solutions in organic

solvents were dried with anhydrous Na₂SO₄. Solvents

were evaporated under reduced pressure on a rotary

evaporator. Thin-layer chromatography was carried out on

aluminium-backed silica gel plates (Merck 60 F₂₅₄) with

visualisation of components by UV light (254 nm) or

exposure to I₂. Column chromatography was carried out

on silica gel, (Merck 230–400 mesh). All compounds desig-

nated for biological testing were analysed at Ͼ99% purity

by reverse phase HPLC using a Philips PU4100 liquid

chromatograph, a Phenomenex BondClone 10-C18 stainless

steel column (300×3.9 mm i.d.) and a Philips PU4120

diode array detector. Chromatograms were run using

various gradients of aqueous (1 M NaH₂PO₄, 0.75 M

heptanesulphonic acid, 0.5 M dibutylammonium phosphate,

and MilliQ water in a 1:1:1:97 ratio) and organic (80%

MeOH/MilliQ water) phases. DCM refers to dichloro-

methane; THF refers to tetrahydrofuran dried over sodium

benzophenone ketyl; DMF refers to dry dimethyl-

formamide; DMSO refers to dimethylsulphoxide; EtOAc

refers to ethyl acetate; ether refers to diethyl ether; light

petroleum refers to petroleum ether, boiling range

40–60ЊC; MeOH refers to methanol; EtOH refers to

ethanol. All solvents were freshly distilled.

NMR d 162.5 (CO₂), 159.9 (CO₂), 139.9 (C-2), 137.4 (C-4),

125.1 (C-5), 61.6 (CH₂O), 61.1 (CH₂O), 34.1 (NCH₃), 14.1

(CH₃) and 13.9 (CH₃); MS m/z 226 (M^ϩ, 30%), 181 (60),

and 153 (100); HRMS calcd for C₁₀H₁₄N₂O₄(M^ϩ) m/z

226,0953, found 226.0960.

4,5-Bis(hydroxymethyl)-1-methyl-1H-imidazole (10). A

solution of diester 9 (5.17 g, 22.8 mmol) in THF (20 mL)

was added dropwise to a stirred suspension of LiAlH₄

(2.60 g, 68.5 mmol) in THF (50 mL) at 0ЊC. The mixture

was stirred for 5 h at 20ЊC and quenched with water (5 mL)

(Caution), 2 M NaOH (2 mL) and water (5 mL). The

suspension was ﬁltered through a pad of Celite and the

residue extracted in a Soxhlet apparatus with THF. The

combined organic fraction was evaporated to give 10

(2.15 g, 66%) as white crystals, mp (THF) 124.5–

1

126.5ЊC; IR n 3329, 1518, 1356, 1221 cm^Ϫ1; H NMR

[(CD₃)₂SO] d 7.46 (s, 1 H, H-2), 4.90 (br t, J5.0 Hz, 1H,

OH), 4.63 (br t, J5.1 Hz, 1H, OH), 4.45 (d, J5.0 Hz, 2H,

CH₂O), 4.30 (d, J5.0 Hz, 2H, CH₂O), and 3.59 (s, 3H,

NCH₃); ¹³C NMR [(CD₃)₂SO] d 139.2 (C-4), 136.9 (C-2),

128.4 (C-5), 56.3 (CH₂O), 51.3 (CH₂O), and 31.1 (NCH₃);

Anal. calcd for C₆H₁₀N₂O₂: C, 50.7; H, 7.1; N, 19.7; found

C, 50.4; H, 7.2; N, 19.5%.

4,5-Bis({tert-butyldimethylsilyloxy}methyl)-1-methyl-1H-

imidazole (11).

A solution of TBDMSCl (12.9 g,

85.5 mmol) in DMF (20 mL) was added dropwise to a

stirred solution of diol 10 (3.04 g, 21.4 mmol) and imida-

zole (3.64 g, 53.5 mmol) in DMF (50 mL) at 5ЊC under N₂.

The solution was stirred at 20ЊC for 96 h and the solvent

removed. The residue was partitioned between EtOAC

(200 mL) and water (200 mL). The organic fraction was

washed with dil. HOAc (50 mL), water ꢀ3×50 mL; brine

(50 mL), dried and the solvent removed. The residue was

chromatographed, eluting with 10% MeOH/EtOAc, to give

11 as a clear oil (5.84 g, 74%), which solidiﬁed on standing,

mp 134–136ЊC; IR n 1516, 1467 and 1254 cm^Ϫ1; ¹H NMR

d 7.29 (s, 1H, H-2), 4.71 (s, 2H, CH₂O), 4.64 (s, 2H, CH₂O),

3.63 (s, 3H, NCH₃), 0.91 (s, 18H, 2OSiC(CH₃)₃), and 0.11

(s, 12H, 2OSi(CH₃)₂); ¹³C NMR d 139.8 (C-4), 136.6 (C-2),

128.5 (C-5), 60.3 (CH₂O), 53.4 (CH₂O), 31.5 (NCH₃),

25.9 (2OSiC(CH₃)₃), 18.3 (2OSiC(CH₃)₃), and Ϫ3.0

(2OSi(CH₃)₂); MS (CI, NH₃) m/z 371 (MH^ϩ, 100%), 355

(5), and 313 (20); HRMS (CI, NH₃) calcd for C₁₈H₃₉N₂O₂Si₂

(MH^ϩ) m/z 371.2550, found 371.2549.

Synthesis of 3

Diethyl 1-methylimidazol-1H-yl-4,5-dicarboxylate (9).

Thionyl chloride (23.4 mL, 320 mmol) was added dropwise

to a stirred suspension of imidazole-4,5-dicarboxylic acid

(10.0 g, 64 mmol) and DMF (3 drops) in EtOH (200 mL)

and the mixture stirred at 80ЊC for 48 h. The solvent was

removed and the residue dissolved in water (100 mL) and

the pH adjusted to 9 with aq. KOH. The solution was

extracted with EtOAc ꢀ4×100 mL; the combined extracts

dried and the solvent removed to give crude diethyl imida-

zole-4,5-carboxylate (8.39 g, 62%), mp (EtOAc) 152.5–

2-Azido-4,5-bis(tert-butyldimethylsilyloxymethyl)-1-methyl-

1H-imidazole (12). A solution of n-BuLi (2.5 M in

hexanes) (4.5 mL, 11.3 mmol) was added dropwise to a

stirred solution of imidazole (4.0 g, 10.8 mmol) in THF

(100 mL) at Ϫ78ЊC. The solution was stirred for 10 min, a

solution of tosyl azide³⁶(Caution) (2.43 g, 11.9 mmol) in

THF (15 mL) added dropwise and the solution stirred at

Ϫ78ЊC for 30 min. The solution was allowed to warm to

20ЊC over 1 h and the reaction quenched with saturated aq.

NH₄Cl solution (4 mL) (Caution). The mixture was poured

into saturated aq. NH₄Cl solution (100 mL) and extracted

with EtOAc ꢀ2×100 mL: The organic fraction was dried,

the solvent removed, and the residue was chromatographed,

eluting with 10% EtOAc/petroleum ether, to give the azide

12 (3.08 g, 69%) as a clear oil, IR n (thin ﬁlm) 2132, 1505

and 1256 cm^Ϫ1; ¹H NMR d 4.67 (s, 2H, CH₂O), 4.61 (s, 2H,

1

155.0ЊC (lit.⁵⁰mp 151–152ЊC); H NMR d 9.20 (br s, 1H,

NH), 7.90 (s, 1H, H-2), 4.38 (q, J7.1 Hz, 4H, 2CH₂O),

1.36 (t, J7.1 Hz, 6H, 2CH₃). A mixture of ester (8.0 g,

37.7 mmol), K₂CO₃(5.5 g, 39.6 mmol) and MeI (2.82 mL,

45.2 mmol) in DMF (50 mL) was stirred at 40ЊC for 24 h.

The solvent was removed and the residue partitioned

between EtOAc (200 mL) and water (200 mL). The organic

fraction was washed with water ꢀ3×50 mL; brine (50 mL),

dried and the solvent removed to give 9 (6.48 g, 76%) as an

1

oil, IR (thin ﬁlm) n 1717, 1506 1377 and 1277 cm^Ϫ1; H

NMR d 7.52 (s, 1H, H-2), 4.39 (2q, J7.1 Hz, 4H, 2CH₂O),

3.85 (s, 3H, NCH₃) and 1.39 (t, J7.1 Hz, 6H, 2CH₃); ¹³C

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

651

CH₂O), 3.38 (s, 3H, NCH₃), 0.91 (s, 9H, OSiC(CH₃)₃), 0.88

(s, 9H, OSiC(CH₃)₃), 0.10 (s, 6H, OSi(CH₃)₂), and 0.06 (s,

6H, OSi(CH₃)₂); ¹³C NMR d 140.0 (C-2), 135.9 (C-4),

126.8 (C-5), 59.2 (CH₂O), 54.2 (CH₂O), 29.6 (NCH₃),

26.1 (OSiC(CH₃)₃), 25.8 (OSiC(CH₃)₃), 18.5 (OSiC(CH₃)₃,

18.1 (OSiC(CH₃)₃, Ϫ5.2 (OSi(CH₃)₂), and Ϫ5.4

(OSi(CH₃)₂); MS m/z 411 (M^ϩ, 1%), 383 (4), 354 (10)

and 326 (100); HRMS calcd for C₁₈H₃₇N₅O₂Si₂(M^ϩ) m/z

411.2486, found 411.2485.

C, 56.05; H, 10.2; N, 10.9; found C, 55.7; H, 10.0; H,

10.7%.

N-[4,5-Bis(tert-butyldimethylsilyloxymethyl)-1-methyl-

1H-imidazol-2-yl]-N-tritylamine (15). A solution of trityl

chloride (0.71 g, 2.53 mmol) in DCM (10 mL) was added

dropwise to a stirred solution of amine 14 (0.93 g,

2.41 mmol) and Et₃N (0.37 mL, 2.65 mmol) in DCM

(50 mL) at 20ЊC under N₂. The solution was stirred for

16 h, diluted with DCM (100 mL), washed with water

ꢀ3×60 mL; brine (50 mL), dried and the solvent removed.

The residue was chromatographed, eluting with 20%

EtOAc/petroleum ether, to give tritylamine 15 (1.40 g,

93%) as a white solid, mp (EtOAc/petroleum ether) 113–

2-Azido-4,5-bis(hydoxymethyl)-1-methyl-1H-imidazole

(13). A solution of TBAF (1 M in THF) (10.5 mL,

10.5 mmol) was added dropwise to a stirred solution of

bis(silyl ether) 12 (2.06 g, 5 mmol) in THF (80 mL) at

Ϫ10ЊC and the solution stirred for 1 h. The solvent was

removed and the residue chromatographed, eluting with a

gradient (0–15%) MeOH/EtOAc, to give diol 13 (0.64 g,

70%) as a white solid, mp (EtOAc) 104ЊC (dec.); IR n

1

116ЊC; IR n 3254, 1493, 1471 and 1254 cm^Ϫ1; H NMR d

7.27–7.30 (m, 6H, H-3⁰, H-5⁰), 7.21–7.25 (m, 6H, H-2⁰,

H-6⁰), 7.16–7.18 (m, 3H, H-4⁰), 4.51 (s, 2H, CH₂O), 4.49

(br s, 1H, NH), 4.39 (s, 2H, CH₂O), 2.92 (s, 3H, NCH₃), 0.84

(s, 9H, OSiC(CH₃)₃), 0.82 (s, 9H, OSiC(CH₃)₃), Ϫ0.01 (s,

6H, OSi(CH₃)₂), and Ϫ0.04 (s, 6H, OSi(CH₃)₂; ¹³C NMR d

145.5 (3, C-1⁰), 145.5 (C-2), 134.5 (C-4), 129.3 (6, C-2⁰

C-6⁰), 127.5 (6, C-3⁰, C-5⁰), 126.8 (3, C-4⁰), 124.3 (C-5),

72.6 (CPh₃), 59.0 (CH₂O), 54.4 (CH₂O), 28.9 (NCH₃), 26.0

(OSiC(CH₃)₃), 25.8 (OSiC(CH₃)₃), 18.3 (OSiC(CH₃)₃), 18.1

(OSiC(CH₃)₃), Ϫ5.1 (OSi(CH₃)₂), and Ϫ5.3 (OSi(CH₃)₂);

MS (DEI) m/z 627 (M^ϩ, 4%), 550 (1), 495 (15) and 243

(100); HRMS (DEI) calcd for C₃₇H₅₃N₃O₂Si₂(M^ϩ) m/z

627.3676, found 627.3646; Anal. calcd for C₃₇H₅₃N₃O₂Si₂:

C, 70.8; H, 8.5; N, 6.7; found C, 70.9; H, 8.8; N, 6.7%.

1

3345, 3221, 2135, 1508 and 1259 cm^Ϫ1; H NMR d 4.93

(br s, 1H, OH), 4.75 (br s, 1H, OH), 4.41 (s, 2H, CH₂O), 4.27

(s, 2H, CH₂O), and 3.35 (s, 3H, NCH₃); ¹³C NMR d 138.3

(C-2), 136.7 (C-4), 128.6 (C-5), 55.6 (CH₂O), 51.3 (CH₂O),

and 29.2 (NCH₃); MS m/z 183 (M^ϩ, 15%), 155 (20), 124

(35) and 42 (100); HRMS calcd for C₆H₉N₅O₂(M^ϩ) m/z

183.0756, found 183.0757.

[2-Azido-1-methyl-4-({[(methylamino)carbonyl]oxy}-

methyl)-1H-imidazol-5-yl]methyl methyl-carbamate (3).

Dibutyltindiacetate (3 drops) was added to a stirred suspen-

sion of diol 13 (0.64 g, 3.5 mmol) and MeNCO (0.45 mL,

7.7 mmol) in DCM (30 mL) and the mixture stirred at 20ЊC

for 16 h. The solvent was removed and the residue chroma-

tographed, eluting with a gradient (0–10%) MeOH/EtOAc,

to give the azido bis-carbamate 3 (0.89 g, 86%) as a pale

yellow solid, mp (EtOAc) 126ЊC (dec.); IR n 3424, 3368,

2172, 2120, 1707, 1560 and 1273 cm^Ϫ1; ¹H NMR d 5.13 (s,

2H, CH₂O), 5.04 (s, 2H, CH₂O), 4.78 (br s, 1H, NH), 4.75

(br s, 1H, NH), 3.38 (s, 3H, NCH₃), and 2.77–2.80 (m 6H,

2CH₃); ¹³C NMR d 156.8 (NCO₂), 156.4 (NCO₂), 141.6

(C-2), 134.9 (C-4), 124.9 (C-5), 59.1 (CH₂O), 54.8

(CH₂O), 29.6 (NCH₃), 27.6 (CH₃), and 27.5 (CH₃); MS

(DEI) m/z 297 (M^ϩ, 5%), 269 (5), 223 (20), 155 (30) and

42 (100); HRMS (DEI) calcd for C₁₀H₁₅N₇O₄(M^ϩ) m/z

297.1189, found 297.1188; Anal. calcd for C₁₀H₁₅N₇O₄:

C, 40.4; H, 5.1; N, 33.0; found C, 40.1; H, 5.2; N, 32.4%.

N-[4,5-Bis(hydroxymethyl)-1-methyl-1H-imidazol-2-yl]-

N-tritylamine (16). A solution of TBAF (1 M in THF)

(4.6 mL, 4.6 mmol) was added dropwise to a stirred solution

of tritylamine 15 (1.38 g, 2.2 mmol) in THF (50 mL) at 5ЊC

and the solution was stirred for 2 h. The solvent was

removed and the residue chromatographed, eluting with a

gradient (0–10%) of MeOH/EtOAc, to give the diol 16

(0.68 g, 77%) as a white solid, mp (MeOH) 168ЊC (dec.);

1

IR n 3431, 3287, 2944, 1603, 1541 and 1448 cm^Ϫ1; H

NMR [(CD₃)₂SO] d 7.33–7.38 (m, 6H, H-3⁰, H-5⁰), 7.20–

7.25 (m, 6H, H-2⁰, H-6⁰), 7.14–7.18 (m, 3H, H-4⁰), 6.16 (s,

1H, NH), 4.57 (t, J5.1 Hz, 1H, OH), 4.26 (d, J5.1 Hz,

2H, CH₂O), 3.95–4.02 (m, 3H, CH₂O, OH), 3.25 (s, 3H,

NCH₃), and 2.53 (s, 3H, CH₃OH); ¹³C NMR [(CD₃)₂SO]

d 146.2 (3, C-1⁰), 145.5 (C 2), 134.0 (C-4), 129.0 (6,

C-3⁰, C-5⁰), 127.1 (6, C-2⁰, C-6⁰), 124.0 (3, C-4⁰), 124.0

(C-5), 70.3 (CPh₃), 56.1 (CH₂O), 51.7 (CH₂O), 48.4

(CH₃OH) and 28.8 (NCH₃); MS (DEI) m/z 399 (M^ϩ, 1%),

281 (15), 304 (10) and 243 (100); HRMS (DEI) calcd for

C₂₅H₂₅N₃O₂(M^ϩ) m/z 399.1947, found 399.1943; Anal.

calcd for C₂₅H₂₅N₃O₂·1/2CH₃OH: C, 73.7; H, 6.6; N,

10.1; found C, 73.3; H, 6.7; N, 10.1%.

4,5-Bis(tert-butyldimethylsilyloxymethyl)-1-methyl-1H-

imidazol-2-ylamine (14). A solution of azide 12 (2.0 g,

4.86 mmol) and Pd/C (0.1 g) in EtOH (50 mL) was stirred

at 20ЊC under H₂(60 psi) for 1 h. The suspension was

ﬁltered through celite, washed with EtOH ꢀ2×10 mL and

the solvent removed to give amine 14 (1.71 g, 91%) as a

colourless solid, mp 128–129.5ЊC; IR n 3380, 3314, 1655,

1

1558 and 1256 cm^Ϫ1; H NMR d 4.63 (s, 2H, CH₂O), 4.52

Reaction of diol 16 with methylisocyanate. Dibutyltindi-

acetate (3 drops) was added to a stirred solution of diol 16

(0.64 g, 1.6 mmol) and MeNCO (0.20 mL, 3.36 mmol) in

DCM (30 mL) at 20ЊC and the solution stirred for 16 h. The

solvent was removed and the residue chromatographed,

eluting with a gradient (0–10%) of MeOH/EtOAc, to

give: (i) N-[4,5-bis(hydroxymethyl)-1-methyl-1H-imidazol-

(s, 2H, CH₂O), 3.87 (br s, 2H, NH₂), 3.38 (s, 3H, NCH₃),

0.91 (s, 9H, OSiC(CH₃)₃), 0.87 (s, 9H, OSiC(CH₃)₃), 0.09 (s,

6H, OSi(CH₃)₂), and 0.05 (s, 6H, OSi(CH₃)₂); ¹³C NMR

d(147.4 (C-2), 133.3 (C-4), 123.6 (C-5), 59.0 (CH₂O),

54.3 (CH₂O), 29.3 (NCH₃), 26.1 (OSiC(CH₃)₃), 25.8

(OSiC(CH₃)₃), 18.5 (2OSiC(CH₃)₃), Ϫ5.2 (OSi(CH₃)₂),

and Ϫ5.3 (OSi(CH₃)₂); MS m/z 385 (M^ϩ, 5%), 370 (8)

and 328 (100); HRMS calcd for C₁₈H₃₉N₃O₂Si₂(M^ϩ) m/z

385.2581, found 385.2577; Anal. calcd for C₁₈H₃₉N₃O₂Si₂

1

2-yl]-N⁰-methyl-N-tritylurea (18) (0.10 g, 14%) H NMR

d 7.15–7.28 (m, 15H, H_arom), 4.83 (br q, J4.8 Hz, 1H,

NH), 4.78 (s, 2H, CH₂O), 4.62 (br s, 1H, OH), 4.39 (s, 2H,

652

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

CH₂O), 4.12 (br s, 1H, OH), 2.92 s, 3H, NCH₃) and 2.67 (d,

J4.8 Hz, 3H, CH₃); ¹³C NMR d 157.7 (NCO₂), 146.0 (C-

2), 145.3 (3, C-1⁰), 130.8 (C-4), 129.3 (6, C-3⁰, C-5⁰), 128.0

(C-5), 127.6 (6, C-2⁰, C-6⁰), 126.9 (3, C-4⁰), 72.9 (CPh₃),

59.4 (CH₂O), 52.9 (CH₂O), 28.8 (NCH₃) and 27.3

(NHCH₃); (ii) starting material 16 (0.11 g, 17%) spectro-

scopically identical to sample prepared above; and (iii)

{4-(hydroxymethyl)-1-methyl-2-[[(methylamino)carbonyl]-

(trityl)-amino]-1H-imidazol-5-yl}methyl methyl-carbamate

(0.40 g, 49%) (19) as a white solid, mp (EtOAc) 186–

dicarbonate (2.4 g, 11.0 mmol) to a stirred solution of amine

14 (1.7 g, 4.4 mmol) and DMAP (0.1 g, 0.9 mmol) in DCM

(100 mL) at 20ЊC and the solution stirred for 16 h. Workup

as above gave 22 (1.66 g, 64%) as a white solid, mp

(EtOAc) 166–167ЊC, spectroscopically identical to the

above sample.

tert-Butyl 4,5-bis(hydroxymethyl)-1-methyl-1H-imidazol-

2-ylcarbamate (21). A solution of TBAF (1 M in THF)

(3.7 mL, 3.7 mmol) was added slowly to a stirred solution

of carbamate 20 (0.82 g, 1.69 mmol) in THF (30 mL) at 0ЊC

and stirred for 1 h. The solvent was removed and the residue

chromatographed, eluting with a gradient (0–10%) of

MeOH/EtOAc, to give carbamate 21 (0.39 g, 90%) as a

white solid, mp (MeOH/EtOAc) 200ЊC (dec.); IR n 3345,

187ЊC; IR

n 3326, 3069, 1738, 1638 ,1545 and

1377 cm^Ϫ1; H NMR d 7.30–7.33 (m, 6H, H_arom), 7.23–

7.27 (m, 9H, H_arom), 4.61 (s, 1H, OH), 4.50 (q, J4.6 Hz,

1H, NH), 4.39 (br s, 1H, NH), 4.33 (s, 2H, CH₂O), 4.26 (s,

2H, CH₂O), 3.00 (s, 3H, NCH₃), 2.78 (d, J4.6 Hz, 3H,

NCH₃), and 2.60 (s, 3H, NCH₃); ¹³C NMR d 158.7

(NCO₂), 154.3 (NCO₂), 146.3 (C-2), 145.3 (3, C-1⁰),

136.4 (C-4), 129.1 (6, C-3⁰, C-5⁰), 127.7 (6, C-2⁰, C-6⁰),

126.8 (3, C4⁰), 119.9 (C-5), 72.6 (CPh₃), 56.9 (CH₂O),

40.0 (CH₂O), 32.2 (NCH₃), 29.1 (NCH₃) and 27.6

(NCH₃); Anal. calcd for C₂₉H₃₁N₅O₃: C, 70.0, H, 6.3; N,

14.1; found C, 69.9; H, 6.8; N, 14.4%.

1

3169, 1728, 1576, 1462 and 1248 cm^Ϫ1

;

¹H NMR

[(CD₃)₂SO] d 9.10 (br s, 1H, OCONH), 4.92 (br s, 1H,

OH), 4.64 (br s, 1H, OH), 4.41 (d, J4.3 Hz, 2H, CH₂O),

4.27 (d, J4.5 Hz, 2H, CH₂O), 3.34 (s, 3H, NCH₃), 3.30 (br

s, 3H, CH₃OH), and 1.43 (s, 9 H, OC(CH₃)₃); ¹³C NMR

[(CD₃)₂SO] d 154.0 (NHCO₂), 145.8 (C-2), 138.0 (C-4),

127.0 (C-5), 79.5 (OC(CH₃)₃, 55.8 (CH₂O), 51.4 (CH₂O),

48.5 (CH₃OH), 29.4 (NCH₃) and 28.0 (OC(CH₃)₃); Anal

calcd for C₁₁H₁₉N₃O₄·0.5CH₃OH: C, 50.5; H, 7.7; N, 15.4;

found C, 50.6; H, 7.6; N, 15.5%.

Reaction of amine 14 with di-tert-butyldicarbonate. A

solution of di-tert-butyldicarbonate (1.06 g, 4.86 mmol) in

DCM (10 mL) was added to a stirred solution of amine

(1.25 g, 3.24 mmol) in DCM (50 mL) at 20ЊC and stirred

for 2 h. The solution was diluted with DCM (150 mL),

washed with water (200 mL), brine (50 mL), dried and the

solvent removed. The residue was chromatographed, eluting

with 30% EtOAc/petroleum ether, to give: (i) tert-butyl 4,5-

bis(tert-butyldimethylsilyloxymethyl)-1-methyl-1H-imidazol-

2-ylcarbamate (20) (0.90 g, 57%) as a white solid, mp 100–

Di(tert-butyl) 4,5-bis(hydroxymethyl)-1-methyl-1H-imida-

zol-2-ylimidodicarbonate (23). HF-pyridine (10 drops)

was added to a stirred solution of bis(silylether) 22

(0.63 g, 1.1 mmol) in THF (50 mL) at 20ЊC and the solution

stirred for 16 h. The solvent was removed and the residue

chromatographed, eluting with 20% MeOH/EtOAc, to give

the diol 23 (0.32 mg, 81%) as a white solid, mp (EtOAc)

101.5ЊC; IR n 2957, 2930, 1719, 1570 and 1283 cm^Ϫ1; H

177–178ЊC; IR n 3246, 1769, 1732, 1516 and 1371 cm^Ϫ1

;

1

NMR d 10.96 (br s, 1H, NH), 4.56 (br s, 2H, CH₂O), 4.50 (s,

2H, CH₂O), 3.46 (s, 3H, NCH₃), 1.49 (s, 9H, OC(CH₃)₃),

0.88 (s, 9H, OSiC(CH₃)₃), 0.85 (s, 9 H, OSiC(CH₃)₃), 0.07

(s, 6H, OSi(CH₃)₂), and 0.04 (s, 6H, OSi(CH₃)₂); ¹³C NMR

d 154.0 (NCO₂), 146.4 (C-2), 138.5 (C-4), 127.8 (C-5), 83.5

(OC(CH3)3), 55.4 (CH₂O), 53.7 (CH₂O), 29.4 (NCH₃), 28.4

(OC(CH₃)₃), 25.9 (OSiC(CH₃)₃), 25.7 (OSiC(CH₃)₃), 18.3

(OSiC(CH₃)₃), 18.1 (OSiC(CH₃)₃), Ϫ5.3 (OSi(CH₃)₂), and

Ϫ5.4 (OSi(CH₃)₂); Anal calcd for C₂₃H₄₇N₃O₄Si₂: C, 56.9;

H, 9.75; N, 8.65; found C, 56.9; H, 10.0; N, 8.69%; and (ii)

di(tert-butyl) 4,5-bis(tert-butyldimethylsilyloxymethyl)-1-

methyl-1H-imidazol-2-ylimidodicarbonate (22) (0.44 g,

23%) as a white solid, mp (EtOAc) 166–168ЊC; IR n

¹H NMR [(CD₃)₂SO] d 4.97 (t, J5.4 Hz, 1H, OH), 4.70 (t,

J5.4 Hz, 1H, OH), 4.46 (d, J5.4 Hz, 2H, CH₂O), 4.70 (d,

J5.4 Hz, 2H, CH₂O), 3.34 (s, 3H, NCH₃), and 1.41 (s,

18H, 2OC(CH₃)₃); ¹³C NMR [(CD₃)₂SO] d 150.1 (2CO₂),

136.6 (C-2), 136.5 (C-4), 128.5 (C-5), 83.2 (2C(CH₃)₃), 56.0

(CH₂O), 51.6 (CH₂O), 29.3 (NCH₃) and 27.3 (2OC(CH₃)₃);

Anal calcd for C₁₆H₂₇N₃O₆: C, 53.8; H, 7.6; N, 11.8; found

C, 53.6; H, 7.55, N, 11.8%.

Di(tert-butyl) 1-methyl-4,5-bis({[(methylamino)carbonyl]-

oxy}methyl)-1H-imidazol-2-ylimidodicarbon-ate (24). Di-

butyltindiacetate (3 drops) was added to a stirred solution of

diol 23 (0.31 g, 0.87 mmol) and methyl isocyanate

(0.11 mL, 1.91 mmol) in DCM (20 mL) and the solution

stirred for 16 h. The solvent was removed and the residue

chromatographed, eluting with 10% EtOAc/petroleum

ether, to give dicarbonate 24 (0.39 g, 95%) as a colourless

oil, IR (thin ﬁlm) n 3380, 1800, 1767, 1721, 1514 and

1

1767, 1655, 1576, 1340 and 1248 cm^Ϫ1; H NMR d 4.68

(s, 2H, CH₂O), 4.51 (s, 2H, CH₂O), 3.38 (s, 3H, NCH₃), 1.60

(s, 9H, OC(CH₃)₃), 1.50 (s, 9H, OC(CH₃)₃), 0.88 (s, 9H,

OSiC(CH₃)₃), 0.85 (s, 9H, OSiC(CH₃)₃), 0.09 (s, 6H,

OSi(CH₃)₂) and 0.04 (s, 6H, OSi(CH₃)₂); ¹³C NMR d

160.4 (NCO₂), 149.4 (NCO₂), 147.3 (C-2), 122.8 (C-4),

121.4 (C-5), 85.2 (OC(CH₃)₃), 77.7 (OC(CH₃)₃), 54.3

(CH₂O), 53.4 (CH₂O), 30.0 (NCH₃), 28.7 (OC(CH₃)₃),

27.8 (OC(CH₃)₃), 25.9 (OSiC(CH₃)₃), 25.7 (OSiC(CH₃)₃),

18.4 (OSiC(CH₃)₃), 18.1 (OSiC(CH₃)₃), Ϫ5.2 (OSi(CH₃)₂),

and Ϫ5.5 (OSi(CH₃)₂); Anal calcd for C₂₈H₅₅N₃O₆Si₂: C,

57.4; H, 9.5; N, 7.2; found C, 57.4; H, 9.5; N, 7.0%.

1

1251 cm^Ϫ1; H NMR [(CD₃)₂SO] d 7.09 (q, J4.3 Hz,

1H, NH), 6.97 (q, J4.3 Hz, 1H, NH), 5.10 (s, 2H,

CH₂O), 4.89 (s, 2H, CH₂O), 3.37 (s, 3H, NCH₃), 2.51 (br

d, J4.3 Hz, 6H, 2CH₃) and 1.40 (s, 18 H, 2OC(CH₃)₃); ¹³

C

NMR [(CD₃)₂SO] d 156.5 (NCO₂), 156.1 (NCO₂), 149.8

(2CO₂), 138.0 (C-2), 133.9 (C-4), 126.0 (C-5), 83.5

(2OC(CH₃)₃), 58.0 (CH₂O), 54.0 (CH₂O), 29.5 (NCH₃)

and 27.3 (2OC(CH₃)₃); MS (DEI) m/z 471 (M^ϩ,10%), 397

(10), 315 (30), 223 (40) and 165 (100); HRMS (DEI)

calcd for C₂₀H₃₃N₅O₈(M^ϩ) m/z 471.2329, found

471.2337.

Di(tert-butyl) 4,5-bis(tert-butyldimethylsilyloxymethyl)-1-

methyl-1H-imidazol-2-ylimidodicarbonate (22). Compound

22 was also prepared by adding a solution of di-tert-butyl

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

653

Synthesis of 5

chromatographed, eluting with

a

gradient (0–10%)

MeOH/EtOAc to give alcohol 28 (2.90 g, 94%) as a white

solid, mp (EtOAc) 93–94.5ЊC; ¹H NMR [(CD₃)₂SO] d 6.83

(s, 1H, H-4), 5.08 (br. s, 1H, OH), 4.40 (br. s, 2H, CH₂O),

3.51 (s, 3H, NCH₃), and 2.48 (s, 3H, SCH₃); ¹³C NMR d

141.9 (C-2), 133.9 (C-5), 127.0 (C-4), 52.8 (CH₂O), 30.3

(NCH₃) and 15.6 (SCH₃); MS m/z 158 (M^ϩ, 100%), 141

(35) and 125 (85); HRMS calcd for C₆H₁₀N₂O₆S

(M^ϩ), m/z 158.0514, found 158.0513; Anal calcd for

C₆H₁₀N₂OS: C, 45.5; H, 6.4; N, 17.7; S, 20.3; found C,

45.5; H, 6.6; N, 17.8; S, 20.0%.

Ethyl 1-methyl-2-sulphanyl-1H-imidazole-5-carboxylate

(26). Sarcosine ethyl ester hydrochloride³⁸(25) (168 g,

1.09 mol) was dissolved in warm formic acid (140 mL)

and a hot solution of sodium formate (82 g, 1.21 mol) in

formic acid (110 mL) was added. The solution was stirred

at 20ЊC for 4 h. Ac₂O (490 mL) was added carefully and the

solution heated at 100ЊC for 1 h. The mixture was cooled to

20ЊC, ﬁltered and the solvent removed. The residue was

suspended in acetone (550 mL), ﬁltered, the solvent

removed and the residue distilled. The fraction that distilled

between 84 and 94ЊC at 0.3 mmHg was collected to give

ethyl N-formylsarcosinate (125 g, 79%) as a yellow liquid,

¹H NMR d (two rotamers) 8.12, 8.04 (2s, 1H, CHO), 4.22,

4.20 (2q, J7.1 Hz, 2H, OCH₂), 4.18, 3.98 (2s, 2H, CH₂),

3.04, 2.93 (2s, 3H, NCH₃), and 1.30, 1.28 (2t, J7.1 Hz, 3H,

CH₃); ¹³C NMR d 168.2 (CO₂), 163.1, 162.9 (CHO), 61.7,

61.4 (OCH₂), 50.9, 45.6 (NCH₃), 35.2, 30.8 (CH₂) and 14.1

(CH₃).

[1-Methyl-2-(methylsulphinyl)-1H-imidazol-5-yl]metha-

nol (29). A solution of MCPBA (4.32 g, 20.0 mmol) in

DCM (50 mL) was added slowly to a stirred solution alco-

hol 28 (3.02 g, 19.1 mmol) in DCM (100 mL) at Ϫ78ЊC.

The solution was stirred at Ϫ78ЊC for 1 h, warmed to

20ЊC, and stirred for 1 h. The solvent was removed and

the residue chromatographed, eluting with a gradient (0–

20%) of MeOH/EtOAc to give sulphoxide 29 (3.28 g, 98%)

as an oil, ¹H NMR [(CD₃)₂SO] d 7.04 (s, 1H, H-4), 5.27 (t,

J5.3 Hz, 1H, OH), 4.50 (d, J5.3 Hz, 2H, CH₂O), 3.82 (s,

3H, NCH₃) and 3.02 (s, 3H, SOCH₃); ¹³C NMR d 146.7

(C-2), 136.4 (C-5), 127.2 (C-4), 52.4 (CH₂O), 37.6

(SOCH₃) and 30.8 (NCH₃); MS m/z 174 (M^ϩ, 30%), 159

(100), 142 (20) and 127 (60); HRMS calcd for C₆H₁₀N₂O₂S

(M^ϩ) m/z 174.0463, found 174.0464.

A suspension of NaOEt (4.92 g, 72.3 mmol) in dry benzene

(20 mL) was added slowly to a stirred solution of ethyl

N-formylsarcosinate (10.0 g, 68.9 mmol) in ethyl formate

(22.3 mL) at 0ЊC. The solution was stirred at 20ЊC for 2 h,

water was (50 mL) added, and the mixture stirred until a

solution formed. The benzene was separated and cHCl

(8.3 mL, 83 mmol) added dropwise to the stirred aqueous

solution at 0ЊC. The solution was stirred for 10 min and

KSCN (8.03 g, 82.7 mL) added in four portions. The solu-

tion was stirred at 100ЊC for 3 h and then stood at 20ЊC for

16 h. The precipitate was ﬁltered, washed with water and air

dried to give ester 26 (3.52 g, 27%) as white needles, mp

[1-Methyl-2-(methylsulphinyl)-1H-imidazol-5-yl]methyl

4-nitrophenyl carbonate (30). 4-Nitrophenyl chloro-

formate (3.63 g, 17.5 mmol) in THF (20 mL) was added

slowly to a stirred solution of alcohol 29 (2.90 g,

16.6 mmol) and pyridine (1.5 mL, 18.3 mmol) in THF

(50 mL) at 20ЊC under N₂. The solution was stirred at

20ЊC for 16 h, diluted with DCM (200 mL), washed with

10% aq. NaHCO₃(50 mL), brine (50 mL) and dried. The

solvent was removed and the residue chromatographed,

eluting with a gradient (0–10%) of MeOH/EtOAc, to give

4-nitrophenylcarbonate 30 (2.70 g, 48%) as an oil, ¹H NMR

d 8.28 (ddd, J9.1, 3.2, 2.1 Hz, 2H, H-3⁰, H-5⁰), 7.38 (ddd,

J9.1, 3.2, 2.1 Hz, 2H, H-2⁰, H-6⁰), 7.34 (s, 1H, H-4), 5.33

(s, 2H, CH₂O), 4.02 (s, 3H, NCH₃) and 3.17 (s, 3H, SOCH₃);

¹³C NMR d 155.3 (CO₂), 152.1 (C-2), 148.2 (C-1⁰), 145.6

(C-4⁰), 131.8 (C-5), 129.6 (C-4), 125.4 (C-2⁰, C-6⁰), 121.7

(C-3⁰, C-5⁰), 59.1 (CH₂O), 38.1 (SOCH₃) and 31.5 (NCH₃);

MS m/z (DEI) 339 (M^ϩ, 80%), 324 (100), 292 (50) and 279

(70); HRMS (DEI) calcd for C₁₃H₁₃N₃O₆S (M^ϩ) m/z

339.0525, found 339.0520.

1

(H₂O) 178–180ЊC; H NMR [(CD₃)₂SO] d 12.86 (s, 1H,

SH), 7.77 (s, 1H, H-4), 4.23 (q, J7.1 Hz, 2H, CH₂), 3.69

(s, 3H, NCH₃), and 1.27 (t, J7.1 Hz, 3H, CH₃); ¹³C NMR d

164.9 (CO₂), 158.3 (C-2), 123.4 (C-4), 120.4 (C-5), 60.4

(NCH₃), 32.4 (CH₂) and 14.0 (CH₃); Anal. calcd for

C₇H₁₀N₂O₂S: C, 45.1; H, 5.4; N, 15.0; S, 17.2; found C,

45.4; H, 5.5; N, 12.2; S, 17.4%.

Methyl 1-methyl-2-(methylsulphanyl)-1H-imidazole-5-car-

boxylate (27). Iodomethane (1.53 mL, 24.6 mmol) was

added to a stirred suspension of ester 26 (3.82 g,

20.5 mmol) and K₂CO₃(2.84 g, 20.5 mmol) in MeOH

(50 mL). The suspension was stirred at 20ЊC for 1 h, ﬁltered

and the solvent removed. The residue was suspended in

EtOAc (50 mL), ﬁltered and the solvent removed to give

methyl sulphide 27 (3.67 g, 96%) as a white solid, mp

(EtOAc) 56–58ЊC; (lit.⁵¹mp 43–45ЊC) H NMR d 7.72

1

[1-Methyl-2-(methylsulphinyl)-1H-imidazol-5-yl]methyl

bis(2-chloroethyl)carbamate (5). A solution of 4-nitro-

phenylcarbonate 30 (2.68 g, 7.90 mmol) in pyridine

(20 mL) was added to a stirred solution of N,N-bis(2-chloro-

ethyl)amine hydrochloride (1.69 g, 9.5 mmol) in pyridine

(80 mL) at 0ЊC. The solution was stirred at 20ЊC for 16 h,

the solvent removed and the residue partitioned between

DCM and 5% aq. citric acid (100 mL). The organic phase

was washed with brine (50 mL), dried and the solvent

removed. The residue was chromatographed, eluting with

a gradient (0–15%) of MeOH/EtOAc, to give carbamate 5

(1.39 g, 52%) as an oil, ¹H NMR [(CD₃)₂SO] d 7.22 (s, 1H,

H-4), 5.19 (s, 2H, CH₂O), 3.85 (s, 3H, NCH₃), 3.68–3.74

(m, 4H, 2NCH₂), 3.59 (t, J6.3 Hz, 4 H, 2CH₂Cl) and 3.03

(s, 1H, H-4), 3.83 (s, 3H, NCH₃), 3.80 (s, 3H, OCH₃) and

2.68 (SCH₃); ¹³C NMR d 160.6 (CO₂), 150.4 (C-2), 137.4

(C-4), 124.2 (C-5), 51.3 (OCH₃), 32.4 (NCH₃) and 14.8

(SCH₃); MS m/z (M^ϩ, 100%), 153 (45) and 121 (30);

HRMS calcd for C₇H₁₀N₂O₂S (M^ϩ) m/z 186.0463, found

186.0456.

[1-Methyl-2-(methylsulphanyl)-1H-imidazol-5-yl]metha-

nol (28). A solution of Superhydride^᭨in (1 M in THF)

(41.2 mL, 41.2 mmol) was added slowly to a stirred solution

of ester 27 (3.67 g, 19.6 mmol) in THF (50 mL) at 0ЊC. The

solution was stirred at 20ЊC for 3 h, water (10 mL) added

carefully and the solvent was removed. The residue was

654

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

(s, 3H, SOCH₃); ¹³C NMR d 154.8 (NCO₂), 147.8 (C-2),

131.1 (C-5), 129.7 (C-4), 56.0 (CH₂O), 48.7 (NCH₂), 48.3

(NCH₂), 42.0 (CH₂Cl), 41.3 (CH₂Cl), 37.6 (SOCH₃) and

30.9 (NCH₃); MS m/z 345 (M^ϩ, 3%), 343 (15), 341 (20),

330 (10), 328 (40) and 326 (100); HRMS calcd for

C₁₁H₁₇³⁷Cl₂N₃O₃S (M^ϩ) m/z 345.0308, found 345.0297;

calcd for C₁₁H₁₇³⁷Cl³⁵ClN₃O₃S (M^ϩ) m/z 343.0338, found

343.0325; calcd for C₁₁H₁₇³⁵Cl₂N₃O₃S (M^ϩ) m/z 341.0367,

found 341.0344; Anal. calcd for C₁₁H₁₇Cl₂N₃O₃S: C, 38.6;

H, 5.0; N, 12.3; Cl, 20.7; S, 9.4; found C, 38.1; H, 5.0; N,

12.1; Cl, 20.3; S, 9.6%.

and 34.3 (NCH₃); Anal. calcd for C₁₂H₁₀N₄O₇: C, 44.7; H,

3.1; N, 17.4; found C, 45.0; H, 3.0; N, 16.7%.

(1-Methyl-2-nitro-1H-imidazol-5-yl)methyl bis(2-chloro-

ethyl)carbamate (6). A solution of 4-nitro-phenylcarbonate

34 (0.68 g, 2.11 mmol) in pyridine (3 mL) was added to a

solution of N,N-bis(2-chloroethyl)amine hydrochloride

(0.75 g, 4.22 mmol) in pyridine (30 mL) under N₂. The solu-

tion was stirred at 20ЊC for 16 h and the solvent evaporated.

The residue was dissolved in DCM (100 mL) and washed

with 2% citric acid solution ꢀ2×50 mL; water (50 mL),

brine (50 mL), dried and the solvent evaporated. The resi-

due was chromatographed, eluting with 50% EtOAc/petro-

leum ether, to give carbamate 6 (0.51 g, 74%) as a cream

solid, mp (EtOAc) 100–101ЊC; IR n 1703, 1489 and

Synthesis of 6

1

1-Methyl-2-nitro-1H-imidazole-5-carboxylate (32). Sodium

hydroxide solution (1 M, 125 mL, 125 mmol) was added

slowly to a stirred suspension of ethyl 1-methyl-2-nitro-

1H-imidazole-5-carboxylate³⁹(31) (5.0 g, 25.1 mmol) in

water (50 mL) and the mixture stirred at 20ЊC until

complete dissolution occurred. The solution was washed

with ether (50 mL), the pH of the solution adjusted to 3

with HCl (5 N) and the mixture extracted with EtOAc

ꢀ3×100 mL: The combined organic fractions were dried

and the solvent evaporated to give carboxylic acid 31

(4.29 g, 100%) as a tan powder, mp 160–161ЊC (lit.⁵²mp

1344 cm^Ϫ1; H NMR d 7.23 (s, 1H, H-4), 5.21 (s, 2H,

CH₂O), 4.05 (s, 3H, NCH₃) and 3.58–3.70 (m, 8H,

2CH₂N, 2CH₂Cl); ¹³C NMR d 154.8 (NCO₂), 144.5 (C-2),

132.1 (C-5), 129.7 (C-4), 56.2 (CH₂O), 50.8 (2CH₂N), 41.6

(2CH₂Cl) and 34.3 (NCH₃); Anal. calcd for C₁₀H₁₄Cl₂N₄O₄

C, 36.9; H, 4.3; N, 17.2; Cl, 21.8; found C, 37.4; H, 4.1; N,

17.2; Cl, 21.8%.

Synthesis of 7

1-Methyl-1H-imidazole-2-carbaldehyde (36). n-Butyllith-

ium (52.7 mL, 0.132 mol) was added dropwise to a solution

of N-methylimidazole (35) (10 mL, 0.125 mol) in dry THF

(150 mL) at Ϫ78ЊC. The solution was stirred at Ϫ78ЊC for

30 min. DMF (19 mL, 0.25 mol) was added and the mixture

allowed to warm to 20ЊC and stirred for 2 h. Water (5 mL)

was added carefully and the mixture partitioned between

EtOAc and water (500 mL) and the organic fraction washed

with water ꢀ2×50 mL; brine (50 mL), dried, and the solvent

removed to give aldehyde 36 (11.2 g, 80%) as a tan solid,

mp (EtOAc/petroleum ether) 36–38ЊC (lit.⁵³mp 38–39ЊC);

¹H NMR d 9.82 (s, 1H, CHO), 7.27 (s, 1H, H-4), 7.12 (s, 1H,

H-5), and 4.03 (s, 3H, NCH₃); ¹³C NMR d 182.2 (CHO),

143.4 (C-2), 131.5 (C-5), 127.3 (C-4) and 34.9 (N-CH₃).

1

(EtOAc) 161–163ЊC); H NMR [(CD₃)₂SO] d 13.60 (br s,

1H, CO₂H), 7.37 (s, 1H, H-4), and 4.20 (s, 3H, NCH₃); ¹³

C

NMR [(CD₃)₂SO] d 160.3 (CO₂), 147.2 (C-2), 133.7 (C-5),

127.0 (C-4) and 35.0 (NCH₃).

(1-Methyl-2-nitro-1H-imidazol-5-yl)methanol (33). A solu-

tion of CDI (7.0 g, 43.1 mmol) and carboxylic acid 32 was

stirred at 20ЊC for 30 min and then added to a stirred solu-

tion of NaBH₄(4.07 g, 108 mmol) in EtOH (10 mL) and the

mixture stirred at 20ЊC for 1 h. HCl (5 M, 20 mL) was added

carefully and the mixture stirred for 30 min. The solvent

was evaporated and the residue chromatographed, eluting

with EtOAc, to give alcohol 33 (2.23 g, 68%) as a cream

solid, mp (EtOAc/petroleum ether) 138–140ЊC (lit.³⁹142–

144ЊC); ¹H NMR [(CD₃)₂SO] d 7.12 (s, 1H, H-4), 5.49 (br s,

(1-Methyl-1H-imidazol-2-yl)methanol (37). A solution of

aldehyde 36 (11.2 g, 0.102 mol) in dry THF (50 mL) was

added to a stirred suspension of LiAlH₄(4.25 g, 0.11 mol) in

THF (100 mL) at 0ЊC. The suspension was stirred at 20ЊC

for 1 h, water (20 mL) carefully added and the suspension

ﬁltered through Celite. The pad was washed with hot THF

(200 mL) and the solvent removed from the ﬁltrate to give

alcohol 37 (10.3 g, 90%) as a white solid, mp (MeOH/iPr₂O)

1H, OH), 4.55 (s, 2 H, CH₂O) and 3.92 (s, 3H, NCH₃); ¹³

C

NMR [(CD₃)₂SO] d 145.6 (C-2), 138.6 (C-5), 126.5 (C-4),

52.9 (CH₂O) and 34.0 (NCH₃).

(1-Methyl-2-nitro-1H-imidazol-5-yl)methyl 4-nitrophenyl

carbonate (34). A solution of 4-nitrophenyl-chloroformate

(0.67 g, 3.34 mmol) in THF (5 mL) was added to a stirred

solution of alcohol 33 (0.50 g, 3.18 mmol) and pyridine

(283 mL, 3.50 mmol) in THF (50 mL) at 20ЊC under N₂.

The solution was stirred at 20ЊC for 16 h, the solvent evapo-

rated, and the residue dissolved in EtOAc (100 mL). The

solution was washed with water ꢀ2×50 mL; brine (50 mL),

dried, and the solvent evaporated. The residue was chroma-

tographed, eluting with 50% EtOAc/petroleum ether, to

give 4-nitrophenylcarbonate 34 (0.87 g, 84%) as a tan

solid, mp (EtOAc) 156.5–157.5ЊC; IR n 1771, 1537 and

1

114–116ЊC (lit.⁵⁴mp 116ЊC); H NMR [(CD₃)₂SO] d 7.05

(d, J1.0 Hz, 1H, H-4), 6.75 (d, J1.0 Hz, 1H, H-5), 5.30

(br. s, 1H, OH), 4.46 (s, 2H, CH₂O), and 3.63 (s, 3H,

N–CH₃); ¹³C NMR d 147.3 (C-2), 126.0 (C-4), 121.8

(C-5), 55.5 (CH₂O) and 32.3 (NCH₃).

[1-Methyl-5-(methylsulphanyl)-1H-imidazol-2-yl]metha-

nol (38). n-Butyllithium (18.4 mL, 29.4 mmol) was added

dropwise to a stirred solution of alcohol 37 (3.0 g,

26.8 mmol) in THF (200 mL) at Ϫ78ЊC. The suspension

was stirred at Ϫ78ЊC for 15 min. tert-Butyllithium

(17.3 mL, 29.4 mmol) was added dropwise and the suspen-

sion stirred at Ϫ78ЊC for 15 min. Methyl disulphide

(5.3 mL, 58.9 mmol) was added and the mixture allowed

to warm to 20ЊC and stirred for 2 h. Water (5 mL) was

1

1359 cm^Ϫ1; H NMR [(CD₃)₂SO] d 8.33 (ddd, J9.1, 3.2,

2.1 Hz, 2H, H-3⁰, H-5⁰), 7.59 (ddd, J9.1, 3.2, 2.1 Hz, 2H,

H-2⁰, H-6⁰), 7.37 (s, 1H, H-4), 5.48 (s, 2H, CH₂O) and 4.00

(s, 3H, NCH₃); ¹³C NMR [(CD₃)₂SO] d 155.1 (OCO₂),

151.4 (C-1⁰), 146.3 (C-4⁰), 145.2 (C-2), 131.5 (C-5), 129.6

(C-4), 125.4 (C-3⁰, C-5⁰), 122.5 (C-2⁰, C-6⁰), 59.4 (CH₂O)

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

655

added carefully and the mixture partitioned between EtOAc

and water (500 mL). The aqueous layer was extracted with

EtOAc ꢀ2×50 mL; the combined organic extracts washed

with brine (100 mL), dried and the solvent removed. The

residue was chromatographed, eluting with a gradient (0–

10%) of MeOH/EtOAc, to give alcohol 38 (2.16 g, 51%) as

eluting with a gradient (0–15%) of MeOH/EtOAc, to give

carbamate 7 (1.02 g, 80%) as a hygroscopic oil, H NMR

1

d 7.40 (s, 1H, H-4), 5.25 (s, 2H, CH₂O), 3.96 (s, 3H, NCH₃),

3.59–3.69 (m, 8H, 2NCH₂, 2CH₂Cl), and 3.04 (s, 3H,

SOCH₃); ¹³C NMR d 154.8 (OCON), 147.2 (C-2), 133.2

(C-5), 129.8 (C-4), 58.2 (CH₂O), 50.9 (NCH₂), 50.2

(NCH₂), 41.7 (CH₂Cl), 41.4 (CH₂Cl), 38.4 (SOCH₃) and

31.6 (NCH₃); MS (DEI) m/z 345 (M^ϩ, 1%), 343 (7), 341

(9), 330 (1), 328 (7), 326 (10) and 173 (100); HRMS (DEI)

calcd for C₁₁H₁₇³⁵Cl₂N₃O₃S (M^ϩ) m/z 341.0368, found

341.0376; calcd for C₁₁H₁₇³⁵Cl³⁷ClN₃O₃S (M^ϩ) m/z

343.0338, found 343.0348; calcd for C₁₁H₁₇³⁷Cl₂N₃O₃S

(M^ϩ) m/z 345.0309, found 345.0311; Anal. calcd for

C₁₁H₁₅N₃O₃S.H₂O: C, 36.7; H, 5.3; N, 11.7; found C,

36.9; H, 5.5; N, 11.6%.

1

a cream coloured solid, mp (EtOAc) 92–94ЊC; H NMR d

6.99 (s, 1H, H-4), 5.46 (br. s, 1H, OH), 4.62 (s, 2H, CH₂O),

3.72 (s, 3H, NCH₃) and 2.24 (s, 3H, SCH₃); ¹³C NMR d

150.0 (C-2), 132.4 (C-4), 125.0 (C-5), 56.0 (CH₂O), 30.0

(NCH₃) and 20.5 (SCH₃); Anal. calcd for C₆H₁₀N₂OS: C,

45.5; H, 6.4; N, 17.7; S, 20.3; found C, 45.3; H, 6.1; N, 17.6;

S, 20.3%.

[1-Methyl-5-(methylsulphinyl)-1H-imidazol-2-yl]metha-

nol (39). A solution of MCPBA (3.05 g, 15.0 mmol) in

DCM (20 mL) was added dropwise to a stirred solution of

alcohol 38 (2.16 g, 13.7 mmol) in DCM (80 mL) at Ϫ78ЊC.

The solution was stirred at Ϫ78ЊC for 1 h, allowed to warm

to 20ЊC and stirred for 1 h. The solvent was removed and the

residue chromatographed, eluting with a gradient (0–20%)

of MeOH/EtOAc, to give sulphoxide 39 (2.16 g, 90%) as a

white solid, mp (MeOH/EtOAc) 102–105ЊC; ¹H NMR

[(CD₃)₂SO] d 7.39 (s, 1H, H-4), 5.49 (t, J5.6 Hz, 1H,

OH), 4.54 (t, J5.6 Hz, 2H, CH₂O), 3.82 (s, 3H, NCH₃)

and 3.01 (s, 3 H, SOCH₃); ¹³C NMR d 151.6 (C-2), 133.0

(C-4), 128.6 (C-5), 55.5 (CH₂O), 38.2 (SOCH₃) and 31.1

(NCH₃); MS m/z 174 (M^ϩ, 25%), 159 (100) and 130 (65);

HRMS calcd for C₆H₁₀N₂O₂S (M^ϩ) m/z 174.0463, found

174.0462; Anal. calcd for C₆H₁₀N₂O₂S: C, 41.4; H, 5.8;

N, 16.1; S, 18.4; found C, 41.3; H, 5.8; N, 16.0; S, 18.1%.

Synthesis of 8

(1-Methyl-5-nitro-1H-imidazol-2-yl)methanol (42). A mix-

ture of N-methyl-5-nitroimidazole⁴²(41) (1.0 g, 7.9 mmol)

and paraformaldehyde (1.4 g, 15.7 mmol) in DMSO

(10 mL) was heated in a sealed tube at 100ЊC for 24 h.

The mixture was cooled to 20ЊC, EtOH (50 mL) was

added, and the suspension was ﬁltered. The ﬁltrate was

evaporated and the residue was chromatographed on

alumina, eluting with a gradient (0–10%) of MeOH/

CHCl₃, to give alcohol 42 (0.71 g, 57%) as a white powder,

mp (CHCl₃) 116–118ЊC (lit.⁵⁵mp 111ЊC); ¹H NMR

[(CD₃)₂SO] d 7.90 (s, 1H, H-4), 5.62 (t, J5.8 Hz, 1H,

OH), 4.62 (d, J5.8 Hz, 2H, CH₂O) and 3.99 (s, 3H,

NCH₃); ¹³C NMR [(CD₃)₂SO] d 151.8 (C-2), 138.8 (C-5),

130.9 (C-4), 56.1 (CH₂O) and 32.9 (NCH₃).

[1-Methyl-5-(methylsulphinyl)-1H-imidazol-2-yl]methyl

4-nitrophenyl carbonate (40). A solution of 4-nitrophenyl-

chloroformate (2.41 g, 11.9 mmol) in THF (10 mL) was

added slowly to a stirred solution of sulphoxide 39

(1.98 g, 11.4 mmol) and pyridine (1.0 mL, 12.5 mmol) in

THF (60 mL) at 20ЊC under N₂. The solution was stirred

at 20ЊC for 16 h, diluted with DCM (150 mL) and washed

with a saturated solution of NaHCO₃(50 mL), dried and the

solvent removed. The residue was chromatographed, eluting

with a gradient (0–15%) of MeOH/EtOAc, to give 4-nitro-

(1-Methyl-5-nitro-1H-imidazol-2-yl)methyl 4-nitrophenyl

carbonate (43). 4-Nitrophenyl chloroformate (1.48 g, 7.4

mmol) in THF (8 mL) was added slowly to a stirred solution

of alcohol 42 (1.10 g, 7.0 mmol) and pyridine (0.62 mL,

7.7 mmol) in THF (50 mL) at 20ЊC under N₂. The mixture

was stirred at 20ЊC for 16 h, then partitioned between

EtOAc and H₂O. The organic layer was washed with satu-

rated aq. NaHCO₃(50 mL), and the solvent evaporated to

give 4-nitrophenylcarbonate 43 (2.04 g, 94%) as a white

solid, mp (EtOAc/petroleum ether) 175–177ЊC; IR n

1

phenyl carbonate 40 (3.13 g, 81%) as an oil, H NMR

1769, 1526, 1476, 1350 and 1261 cm^Ϫ1

;

¹H NMR

[(CD₃)₂SO] d 8.33 (ddd, J9.1, 3.3, 2.1 Hz, 2H, H-3⁰,

H-5⁰), 7.60 (ddd, J9.1, 3.3, 2.1 Hz, 2H, H-2⁰, H-6⁰), 7.55

(s, 1H, H-4), 5.44 (s, 2H, CH₂O), 3.90 (s, 3H, NCH₃) and

3.07 (s, 3H, SOCH₃); ¹³C NMR d 155.1 (OCO₂), 151.5

(C-2), 145.4 (C-1⁰), 145.2 (C-4⁰), 134.4 (C-5), 129.4

(C-4), 125.3 (C-2⁰, C-6⁰), 122.5 (C-3⁰, C-5⁰), 61.5 (CH₂O),

38.3 (SOCH₃) and 31.4 (NCH₃); MS (DEI) m/z 339 (M^ϩ,

20%), 324 (60) and 57 (100); HRMS (DEI) calcd for

C₁₃H₁₃N₃O₆S (M^ϩ) m/z 339.0525, found 339.0524.

[(CD₃)₂SO] d 8.33 (ddd, J9.1, 3.2, 2.2 Hz, 2H, H-3⁰,

H-5⁰), 8.11 (s, 1H, H-4), 7.59 (ddd, J9.1, 3.2, 2.2 Hz,

2H, H-2⁰, H-6⁰), 5.48 (s, 2H, CH₂O) and 3.97 (s, 3H,

NCH₃); ¹³C NMR [(CD₃)₂SO] d 155.0 (OCO₂), 151.3

(C-2), 145.9 (C-1⁰), 145.2 (C-4⁰), 139.5 (C-5), 131.6

(C-4), 125.3 (C-2⁰, C-6⁰), 122.4 (C-3⁰, C-5⁰), 61.7 (CH₂O)

and 33.5 (NCH₃); Anal. calcd for C₁₂H₁₀N₄O₇C, 44.7; H,

3.1; N, 17.4; found C, 44.9; H, 3.0; N, 17.3%.

[1-Methyl-5-(methylsulphinyl)-1H-imidazol-2-yl]methyl

bis(2-chloroethyl)carbamate (7). A solution of 4-nitro-

phenyl carbonate 40 (1.27 g, 3.74 mmol) in pyridine

(10 mL) was added to a stirred solution of N,N-bis(2-chloro-

ethyl)amine hydrochloride (0.80 g, 4.49 mmol) in pyridine

(50 mL) at 0ЊC. The solution was stirred at 20ЊC for 16 h

and the solvent removed. The residue was partitioned

between DCM and 5% citric acid solution (100 mL) and

the organic fraction washed with brine (50 mL), dried and

the solvent removed. The residue was chromatographed,

(1-Methyl-5-nitro-1H-imidazol-2-yl)methyl bis(2-chloro-

ethyl)carbamate (8). A solution of 4-nitro-phenylcarbonate

43 (2.0 g, 6.5 mmol) in pyridine (5 mL) was added to a

stirred solution of N,N-bis(2-chloroethyl)amine hydro-

chloride (1.5 g, 8.4 mmol) in pyridine (30 mL) at 0ЊC. The

solution was stirred at 20ЊC for 16 h, then solvent was

evaporated and the residue was partitioned between DCM

and 10% aq. citric acid. The organic layer was dried and the

solvent evaporated, and the residue was chromatographed,

eluting with 50% EtOAc/light petroleum, to give carbamate

656

M. P. Hay et al. / Tetrahedron 56 (2000) 645–657

8 (2.0 g, 95%) as an oil, ¹H NMR d 7.99 (s, 1H, H-4), 5.27

(s, 2H, CH₂O), 4.03 (s, 3H, NCH₃) and 3.60–3.71 (m, 8 H,

2CH₂N, 2CH₂Cl); ¹³C NMR d 154.8 (NCO₂), 146.9 (C-2),

139.6 (C-5), 132.2 (C-4), 58.7 (CH₂O), 51.1 (2CH₂N), 41.8

(2CH₂Cl), and 39.7 (NCH₃); MS m/z 328 (M^ϩ, 10%), 326

(55), 324 (75), 289 (70), 245 (75) and 231 (100); HRMS

calcd for C₁₀H₁₄Cl₂N₄O₄(M^ϩ) m/z 324.1392, found

324.1381.

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Compounds were dissolved directly in culture medium

(aMEM containing 5% foetal calf serum), ﬁlter sterilised,

and the drug concentrations were checked by spectro-

photometry. Solutions were used within 1–2 h. BCEA was

dissolved in 0.01N HCl and diluted into the culture medium

immediately before use. Growth inhibition under aerobic

conditions was assessed using log-phase cultures in 96

well plates. Cells were exposed to drugs for 4 or 18 h, the

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blue 3 days later to determine cell density.⁵⁶IC₅₀values

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CO₂in air or N₂, respectively) single cell suspensions as

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Acknowledgements

The authors thank Dr Maruta Boyd for assistance with NMR

spectroscopy and Susan Pullen for biological testing. This

work was supported by the National Cancer Institute, USA

(Contract no. 1-CM-47019), the Marsden Fund of New

Zealand (M. P. H.), the Health Research Council of New

Zealand (W. R. W.), and the Auckland Division of the

Cancer Society of New Zealand (W. A. D.).

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Design, synthesis and evaluation of imidazolylmethyl carbamate prodrugs of alkylating agents

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