Patai S., Rappoport Z. 1997 The chemistry of functional groups. The chemistry of double-bonded functional groups / 0909 110

17. Syntheses and uses of isotopically labelled compounds

979

beams of only 10 15 A cannot be used in the above procedure. The [11C]cyanide can also be prepared250 in high yield in a simple on-line gas-flow system using a low-energy cyclotron by producing [11C]CO2 by irradiation of N2 gas, combining it in line with H2, drying, mixing on line the 11CO2/H2 with NH3 (desiccated over solid KOH) and finally passing the [11C]CO2 H2 NH3 mixture through a quartz tube, containing platinum wire, installed in a furnace held at 950 °C. The [11C]cyanide is extracted from the outflow from the quartz tube in a glass column packed with quartz wool impregnated with NaOH. The trapped radioactivity has been eluted with water. The radioactivity of the starting [11C]CO2 was comparable to the radioactivity of the produced [11C]CN .

1			R1
R
R2	1. [11C]CN −, NaHSO3 , H2 O		R2
	55°C, 5 min, extactions with ether
	or 2. [11C]HCN, methanolic acetate buffer (pH 5.4)
	1-2 units of enzymea ,b , RT, 10 min, work up
CHO		N11C	OH

(239a) R1 = OH, R2 = H

(238)

(239b) R1 = H. R2 = OH

	(a) enzym for 239a: hydroxymandelonitrile lyase
	(b) enzym for 239b: mandelonitrile lyase		(128)
	1 M THF, 55 °C, 8 mi n, work-up
		BH3	− THF

R1

R2

11

HO CH2 NH2

(237a) R1 = OH, R2 = H

(237b) R1 = H, R2 = OH

(b) Optimization of earlier methods of 240 production from [11C]CO2 for routine synthesis of [1-11C]amino acids has been investigated by lwata and coworkers251. More than 95% radiochemical yields of 240 have been obtained at 5 vol% of NH3. 99% yield of 240 was achieved when metallic sodium coated on quartz wool was used to adsorb traces of O2 which interfere with the catalytic reaction of [11C]CH4 with NH3 on Pt. Higher NH3 concentration prevents the oxidation of [11C]CH4. Higher flow rates and shorter contact time gave higher conversion yield of [11C]CH4 to 240. High yield of 240 was obtained over the temperature interval 850 to 950 °C. Above 950 °C a slight decrease in yield of 240 was observed due to its decomposition. The effect of the Pt amount on the yield of 240 was also studied.

980	Mieczysław Ziełinski´ and Marianna Kanska´

(c) As regards synthesis of NCA [11C]amino acids from 240, the optimal conditions for the synthesis of NCA[111C]amino acids according to the procedure shown in equation 129 have been chosen251. The best reaction temperature, time and HCl concentration for acid hydrolysis of aminonitriles were found to be 160 °C, 15 min and 6N, respectively. The replacement of the bisulphite group by [11C]cyanide proceeded quantitatively. The following [1-11C]amino acids have been prepared according to the above procedure within about 1 h: phenylglycine, ˛-methylphenylglycine, cyclohexylglycine, phenylalanine, aminocyclohexanecarboxylic acid, aminocyclopentanecarboxylic acid, valine, leucine and norleucine in about 50% radiochemical yield. The method of equation 129 is suitable for automation of [1-11C]amino acid production.

							OH		NH4 OH		NH2
		O + NaHSO3
R1R2 C					R1R2 C					R1R2 C
							SO3 Na				SO3 Na
								60 °C, 10 min
										11CN −	(129)
				11 COOH					11CN
		R1R2 C					R1R2 C
				NH2					NH2

B. Compounds Labelled with Carbon-14

1. Synthesis of [1-14C]-2-2-difluoroethene (241)

1,1-Difluoroethene (DFE) is a volatile industrial monomer widely used in the production of a variety of polymers. DFE-induced hepatotoxicity and acetonemia have been detected in the rats252 254. 241 has been therefore synthesized255 to expedite study of the metabolic fate of the carbon fragment of 241 (equation 130). 241 has been obtained in low yields of 10 15%, caused by trace amounts of water which destroy the intermediates 243 and 242 (equations 131 and 132).

O

O

O

(EtO)2 PCF2 H

LDA

(EtO)2 PCF2 Li

Me3 SiCl

(EtO)2 PCF2 SiMe3

(243)

CsF (cat.), RT

over night under N2

O

14 CH2 O / THF

(130)

(EtO)2 PCF2

14 CH2 OSiMe3

4 h reflux under flow of helium

14 CH2

F2 C

CsF

(242)

(241)

O

+

(EtO)2

PO−Cs+ +

Me3 SiF

O

243

H2 O

(131)

(EtO)2 PCF2 H

CsF

17. Syntheses and uses of isotopically labelled compounds							981
		O
242	H2 O						(132)
		(EtO)2 PCF2 14 CH2 OH

CsF

2. Synthesis of 3-phenoxy[1-14C]- and 3-phenoxy[3-14C]propene (244 and 245)

244 and 245 have been synthesized258 (equations 133 and 134) for 14C KIE studies in the Claisen rearrangement.

HOCH2 CH2 Cl

KCN/EtOH/H2 O

conc. HCl

HOCH2 CH2 CN

ClCH2 CH2 COOH

2. conc. HCl

1. PhOH, KOH/H2 O

LiA lH4

Me2

NCOCl

PhOCH2 CH2 CH2 NMe2

PhOCH2 CH2 CNMe2

PhOCH2 CH2 COOH

benzene/Py

MeI/EtOH

O

+

1. A gOH/H2 O, RT, 20h

PhOCH2 CH

−

CH2

PhOCH2 CH2 CH2 NM3 I

2. 160°C,

∆, work-up

(244)

(133)

A c2 O

dry EtOH, p-TSA / CHCl3

CH3 COOH

ClCH2 COOH

ClCH2 COOEt

Cl2

LiA lH4 / A lCl3 / ether

KCN

HOCH2 CH2 CN

ClCH2 CH2 OH

as i n equation 133

as in equation 133

(134)

PhOCH2 CH CH2

(245) 2.1% overall yield

= 14 C label

3.Synthesis of [2,3,4,5-14C]-1-vinylpyrrolidinone (246)

NVP, 246, is the intermediate in the production of PVP (polyvinylpyrrolidinone)257 widely employed in the pharmaceutical, medicinal, food and beverage industries, and the small quantities (0.2% or less) of NVP contained as impurity in PVP might present a certain risk for the general population. Studies on the in vivo disposition of NVP have therefore been undertaken and 246 has been synthesized258 (equation 135). [3,4-3H]-NVP and [4-3H]-NVP have been prepared previously in low yields259 because the volatility of NVP itself and of the vinyl acetate had not been controlled properly in the synthetic and

982	Mieczysław Ziełinski´ and Marianna Kanska´

separation procedures.

H2 N COOH

	1. HMDS / MeCN
	2. MeOH
			NH	O
			(247)
	Na2 PdCl4 / K2 CO3

N O

HMDS = hexamethyldisilane

(246)

(135)

CH2 CHOOCCH3

4. Synthesis of 14C-labelled catechol-O-methyltransferase inhibitors

The two title COMT enzymes (inhibitors), which may open new possibilities for the treatment of Parkinson’s disease260,261, namely 3-(3,4-dihydroxy-5-nitropenylmethyli- dene)-2,4-pentadione (248) and E-N,N-diethyl-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl) acryloamide (249), have been labelled262 with carbon-14 using [carbonyl-14C]vanillin as the starting compound (equation 136). [14C-]-248 and- 249 are necessary in studies of the mechanism and pharmacokinetic properties of these drugs.

		MeO	CHO
MeO	CHO
	HNO3	/ CH2 Cl2
HO		HO
		NO2
	3.6 mCi
		48% HBr
		HO		COCH3
HO	CHO

2, 4-pentanedione / THF / toluene

COCH3 (136)

HO		HO
NO2		NO2
			(248)
			O
N, N-diethyl-2-cyanoacetamide, piperidine,	HO		N
acetic acid, molecular sieves
			CN
	HO

NO2

(249)

17. Syntheses and uses of isotopically labelled compounds

983

5. Synthesis of [14C]-labelled eutypine (250)

The 4-hydroxy-3-(3-methyl-3-buten-1-ynyl)benzaldehyde, 250, a phytotoxic compound responsible for vineyard die-back, has been [14C]-labelled263 via Wittig reaction using [14C]CH3I as precursor (equation 137).

CHO	OH			OH
	7 steps	O		CH2
			PPh3 CH2 / THF
OH	OMOM	1. CH2 Cl2	/ CrO3 − Py2	OMOM
			2. hydrolysis	(137)

CHO

CH2

OMOM = methoxymethyloxy	OH
	(250) [14 C] Eutypine

6. Synthesis of [methoxy-14C]eugenol (251)

251 has been synthesized264 in reaction of mesylate 252 with 14CH3I (equation 138). 251 has been needed to evaluate the transfer and fate of eugenol during the smoking of clove cigarettes, to determine its deposition in various organs of rodents exposed to clove cigarette smoke and to investigate the related health effects265.

OH	OSO2 Me	OSO2 Me
OMe	OMe	OH
	MeSO2 Cl	BBr3
	CH2 Cl2
CH2	CH2	CH2
		(252)
		(138)
		14 MeI, K2 CO3
	OSO2 Me	OH
	O14 CH3	O14 CH3
	NaOH, MeOH
	CH2	CH2

(251) 95%yield

984	Mieczysław Ziełinski´ and Marianna Kanska´

7. Synthesis of 14C-labelled prinomide (253)

Prinomide, 253, a potential aspirin-like NSAID266 (non-steroic anti-inflammatory drug) and its metabolite 254 have been synthesized267 following as in equations 139 141. 253a, 253b and 254 are used in pharmacokinetic and metabolism studies267,268.

1. n-BuLi 2. 14 CO2		14 COOH		CH2 N2		14 COOMe
N	N				N
Me	Me				Me
					NaH, CH3 CN
CN
14 C	NHPh	PhN	C	O	14 C
						CN
N					N
OH	O				O
Me					Me
[14 C] -(253a)						(139)
C	CN +	O	C	N
N
O
Me
	CN					(140)
		NH
N	C
Me	OH	O

[U-14 C]-(253b)

= uniformly 14 C ring labelled

8.Synthesis of [3-14C]acetocetate (255)

255 and other labelled ˇ-keto esters have been obtained in quantitative yield for the synthesis of many types of pharmaceuticals269 by heating of magnesium ethyl malonate with labelled 1-[14C]acetylimidazole followed by acid hydrolysis and decarboxylation (equation 142).

9. Syntheses of [14C]labelled ketones
Numerous [14C]labelled ketones have been synthesized270	by the acylation
of trimethylsilyl-2-lithiomalonates and trimethylsilyl-2-lithioalkane	carboxylates with

17. Syntheses and uses of isotopically labelled compounds

985

[1-14C]acyl halides (equation 143) and applied for the synthesis of different [14C]labelled compounds, mainly biochemicals. A whole variety of labelled acyl halides, prepared from corresponding [14COOH]acids, synthesized directly from 14CO2 or via the [14C]cyanide route, have been utilized in reaction 143. 14C-Labelled biochemicals such as chlorophacinone, amphetamine, olivetol, heptadecane, indole, pyridazine derivatives, 5-aminolevulinic acid, noradrenaline, showdomycine, myosmine, nornicotine, nicotine, cotinine, norcotinine, coniine, palmitic or stearic acid, and other compounds, have been prepared by the method outlined in equation 143 by Pichat270.

CNCH2 Cl / ether / HCl

N

N

Cl

Me

Me

O

K14 CN / 18-crown / MeCN

14 CN

14 CN

N

NHC6 H4 OMe-p

p-MeOC6 H4 N

C

O

(141)

N

Me

O

O

Me

O

BBr3

14 CN

NHC6 H4 OH-p

N

Me

OH

O

O

[14 C]-(254)

R

O

R

COOEt

N

+

Mg

(142)

N

O

O

O

= carbon-14 label

OEt

(255)

O

(143)

R1COX + R2CLi(COOTMS)

2

R1COCR2(COOTMS)

H+

R1

CCH2 R2

2

R2 D H, Me, Et, Pr, Bu, CH2COOTMs, CHMeCOOTMS, NHAc, CH2CN,

CH2CH2CN, (EtO)2CH2CH2 , CH2 mCOOTMS

10. Synthesis of [phenyl-14C]benzazepine derivative SK and F 103829-J

99% pure [6-14C]SK and F 103829-J, 256, has been prepared271 in 10% overall radiochemical yield from 14CH3I and the key substrate, enol lactone, 257 (equation 144).

11. Synthesis of methyl 3-oxo-4,4-dimethylpentanoate-1,3 14C (258)

258 has been synthesized272 as shown in equation 145.

986 Mieczysław Ziełinski´ and Marianna Kanska´

12. Synthesis of [ 14C]-fentanyl (259)

259, a potent opioid analgesic with a faster onset and shorter duration than morphine273,274, has been 14C-labelled275 in the anilidopiperidine substructure, resistant to metabolic extraction of the 14C-label, using [UL-14C]aniline as a source of carbon-14 (equation 146).

	NBn	MeMgI
		O
			O
O	O		Me
	(257)
	NBn
MeO		O

MeSO2

NH.MsOH

HO

(256)

Mg

14 CO2

2MeLi

Me3 CCl

Me3 CMgCl

Me3 C14 COOH

14 CO2

Me3 C14

CCH2

14 COOMe

CH2N2

Me3 C14

CCH2 14 COOH

O

O

(258)

13. Synthesis of the cardiotonic agent 14C-loprinone (260)

NBn

NBn

(144)

Me3 C14 COMe

NaNH2

(145)

14 − +

Me3 C CCH2 Na

O

260 presently under development276 for the treatment of congestive heart failure, has been 14C-labelled for pharmacokinetic profile studies277. 260 (14C-loprinone hydrochloride) has been synthesized using 262 (equation 147).

14. Synthesis of [ 14C]-labelled perlrinone (263)

263, a potent inotropic agent (AY-28, 768 hydrochloride), selected for clinical

development278, has been 14C-labelled in four steps (equation 148) for metabolic studies279.

	17. Syntheses and uses of isotopically labelled compounds					987
O
					CH2 CH2 Ph
+		NaBH(A cO)3	/ THF		N
N				NH
CH2 CH2 Ph	NH2 .HCI
				EtCOCl, RT
						(146)
		N	CH2 CH2 Ph
					14	C]
					= [UL -

N

OEt

(259)18% overall r. yield, r. purity > 99%, sp. act. 2.4 mCi/mmol

N

	1. Mg, EtBr / THF
N	2. ClCH2 CMe
Br		CH2
				O3 / dil. HCl-MeOH
		O
			Me2 NCH(OMe)2		O
			DMF
		N			(147)
		(261)
MeONa / EtOH
	NCCH2 CONH2 , 262
			N
	CN		N		CN
		HCl / EtOH
					HCl.H2 O
NH	O			NH	O

(260)

988

Mieczysław Ziełinski´ and Marianna Kanska´

1. NaCN

ClCH2

COOH

NCCH2 COOEt

2. EtOH,

1. CS2 ,KOH / dioxane, 15 − 20 ˚C

H2 SO4

O

NH

2. (MeO)2 SO2 / EtOH, 0

°C

N

CN

1. CH3 CNH2 .HCl, NaH / DMF,

MeS

2. conc.HCl

CN

Me

MeS

COOEt

NH

SMe

3-aminomethylpyridine

(148)

Dimethoxyethane, 18 h reflux

O

CN

N

Me

NH

NH

N

= position of14

C label

(263)

15. Synthesis of [2-14C]-labelled 2,20 -anhydrouridine (264) 20 -deoxyuridine derivatives (265) and 5-ethynyl- and 5-ethyl-20-deoxyuridine (266)

The title compounds 264 266, possessing significant activity against the Herpes simplex viruses280,281, have been synthesized282 according to equation 149. The higher specific activity of 266b than that of 264 is caused probably not by the 14C KIE in the transfor-

	N		N
mation of	C	bond system in 264 into	C	bond system in 267 but by
O		N	O	N

the smaller LSC counting efficiency of not well dried [2-14C]264 sample.

16. Synthesis of 14C-labelled azasteroids

The azasteroids 268 and 269 of potential clinical utility for the treatment of acne, hirsutism or prostatic hypertrophy, have been 14C-labelled in ring A and the t-butyl portion of carboxamide for metabolism and bioavailability studies283.

17. Synthesis of [phenyl-U-14 C]tefluthrin (270)

270, a synthetic insecticide active against soil pests, has been 14C-labelled284 for metabolism and residues studies (equation 150).

18. Disposition of [14C]prinomide (271) in normal subjects

The disposition of this new 14C-labelled anti-inflammatory drug, 271, and its metabolite, 272, in 4 volunteers has been studied285. The elimination half-life of 271 was about