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			939
O	O
NH	HN
(105) +		1. MeOH, 1 M NaOH, EDTA (hydrolysis)
N	HN	2. NaBH3 CN / EtOH, 5-10 °C, 30 min (reduction)
			(47c)
MeOOC		COOMe

O O

NH HN

NH HN

HOOC

COOH

(102)

IXα-Bilirubin, m.p. 235 °C (decomp.) EDTA = Ethylenediaminotetraacetic acid

C. Compounds Labelled with Nitrogen-15

1. Synthesis of mono-15N-cyanogen (106) and mono-13C-cyanogen (107)

106 and 107 have been obtained89 in procedures respectively involving dehydration of mono-15N, 108, and mono-13C-oxamide, 109, with phosphorus pentoxide (equations 48 and 49).

The two symmetrically labelled isotopomers of cyanogen, 15NCC15N and N13C13CN, have been prepared89 by thermolysis of 15N and 13C-silver cyanide, respectively. 106 and 107 have been needed for infrared spectral investigations. The cyanogen, NCCN, was detected in the atmosphere of the Saturn moon Titan90 and the chemical spectroscopic and theoretical studies of the C2N2 isomers have been reviewed91 93.

O

O

O

O

15NH4 Cl, NaOH / H2 O

15

P2

O5 15

EtOC

CNH2

H2

NC

CNH2

NC-CN

four hours

(108)

(106)

23.5% yield

(48)

940

Mieczysław Ziełinski´ and Marianna Kanska´

EtO

K13 CN, CH Cl

A bs. Et2 O, EtOH

ClCOOEt

2

2

N13 CCOOEt

13 C

COOEt

HCl (gas)

+ NH2 Cl−

Et 2 O / H2 O

H2 N

NH2

EtO

N13

CCN

P2 O5

13 C

C

A bs. Et OH, conc. NH4 OH

13

C

COEt

O

O

O

O

(107)

21.2% yield

(109)

(49)

2. Synthesis of urocanic acids multilabelled with 2H, 13C and 15N

(a) [3-2H, 10,30 -15N2]urocanic acid, 110, and [2, 3, 50-2H3, 20 -13C, 10 ,30 ,-15N2]urocanic acid, 111, have been synthesized94 by the enzymatic reaction of DL-[3,3-2H2, 10,30 - 15N2]histidine, 112 (equation 50) and DL-[2,3,3,50 -2H4, 20 -13C, 10,30 -15N2]histidine, 113 (equation 51), respectively. Reaction 51 has been carried out in a D2O buffer system to avoid the enzyme-catalysed hydrogen exchange at C 50 of the imidazole ring95.

		D	D							D
15				COOH	Histidine ammonia lyase						COOH
	N							15 N
			H	NH2
					i n H2 O buffer (pH 9.0) at 25 ° C						(50)
	15 NH							15 NH
	(112)							(110) 85% yield
						(from L-isomer in labelled racemic histidine)
			D	D						D
	15			COOH					(4′ )		(2) COOH
		N				Histidine ammonia lyase		15 N		(3)
			D	NH2					′ )		(1)
13 C								(3		(5 ′ )	(51)
								C(2 ′ )	13
											D
	15 NH		D					(1′ )			D
								15 NH
			(113)							(111)
					75% yield from L-isomer in labelled racemic histidine

110 and 111 have been obtained to investigate the pharmacokinetics of L-histidine in humans. 112 and 113 have been synthesized previously96,97 to detect the heterozygote state98 of histidinemia, a hereditary metabolic disorder, caused by deficiency of the liver enzyme, histidine ammonia lyase99, characterized by mental and/or speech retardations.

17. Syntheses and uses of isotopically labelled compounds

941

(b) The mechanism of the enzymatic elimination of ammonia from L-histidine, catalysed by histidine ammonia lyase (EC4.3.1.3), has been reinvestigated95 by carrying out the synthesis of L-[3,3,50 -2H3, 30 -15N]histidine, 114, starting from [3,3,5,5-2H4]-2,5-diamino- 4-oxo-pentanoic acid96. The isolated urocanic acid product (UA-3,50 -D2), 115, was found to contain protons at the C 50 position of the imidazole ring, and its NMR spectrum indicated 44% loss of deuterium at C 50 . Practically the same value (45.3%) of deuterium loss was obtained from the GC-MS selected ion monitoring data. Without the use of the enzyme the deuterium at C 50 of histidine 114 was found to be retained completely.

When DL-[2,50 -2H2]histidine has been used, 42% deuterium loss was observed. No deuterium loss at C 2 was found. These losses of deuterium at C 50 during the enzymatic reaction have therefore been interpreted as the result of the enzyme-catalysed hydrogen exchange, The incubation of the unlabelled L-histidine with histidine ammonia lyase under the D2O-buffer conditions (pD 9.0) led to ca 20% incorporation of deuterium at C 50 of

urocanic acid (by 1H NMR). The above D/H and H/D exchange data have been taken as excluding the possibility of a concerted mechanism of elimination of ammonia from L-histidine, illustrated by path A in equation 52, and as favoring the stepwise mechanism via a carbanion intermediate illustrated by path B.

			B − D								H
	H	COO−		−	H	−	15	N		CD	COO−
15N	CD2	Path B	15N	CD	COO
										−	+NH3
		Stepwise			+ NH3
	+NH3							NH		D
NH	D		NH	D
His- 3, 3, 5′ -D (114)					enzyme						enzyme
	Path A
Concerted					H+	− H+ or − D+
H	D						CD		H	COO−
	CD H	COO−			15N
							a	D			(52)
N									+
	+NH3				NH			H	NH3
							b
NH	D					(116)
	enzyme								enzyme
					a				b
			CD	COOH					CD		COOH
		15N
						15N

	NH	D
		NH
		urocanic acid

(115)

942	Mieczysław Ziełinski´ and Marianna Kanska´

Neglecting the possibility of occurrence of intramolecular hydrogen/deuterium kinetic isotope effect in the competitive rupture of the C 50 H versus C 50 D bonds in the unstable intermediate 116 and taking into account99,100 the stereospecific abstraction of C 3 hydrogen (pro-3R) followed by delocalization of the 3-carbanion to C 50 , Furuta and coworkers95 proposed the reaction scheme (equation 53) explaining the ca 45% deuterium exchange at C 50 . According to this scheme the stereospecific hydrogen incorporation at C 50 from the solvent is followed by subsequent non-stereospecific loss of a proton at C 50 and formation of urocanic acid retaining 50% deuterium (equation 53). The elimination mechanism of ammonia is a subject of controversy101,102. After the preliminary deuterium and tritium exchange and T/H, D/H, T/D kinetic isotope effect studies, the microscopic mechanisms of the non-enzymic elimination reactions are usually investigated by the heavy-atom isotope effect103 method involving the successive isotope labelling techniques using 13C, 14C and 15N. KIE determinations of 14C and 15N permit one to distinguish between the carbonium ion E1 mechanism, the concerted E2 mechanism and carbanion E1cb mechanism and to establish the relative degrees of the C 3 H and C 2 N bond ruptures in the activated complex which is not indicated explicitly in the reaction schemes shown in equations 52 and 53.

HR

Hs

Hs

COO−

COO−

N

H

NH3 +

stereospecific

N

−

NH3

+

H

abstraction

NH

D

(C(3 ) − H)

NH

D

Stereospecific

+ H

L-His

incorporation

carbanion

at C(5 ′ )

HS

HS

COO−

COO−

(53)

N

N

D

NH3 +

non-stereospecific

H

NH

H

loss C(5 ′ ) H

NH

H

urocanic acid

HS

COO−

N

+

NH

D

3. Synthesis of 15N-labelled nylon 6 (117)

117 has been synthesized104 by anionic polymerization of ε-caprolactam, 118 (equation 54), for investigations of the morphology of this commercially important

17. Syntheses and uses of isotopically labelled compounds

943

polymer by solid-state 15N NMR, IR and Raman spectroscopies.

O

NH

NH2 OH-HCl

H2 SO4

O

NOH

K2 CO3 , H2 O

anionic

(118)

(54)

polymerization

NH(CH2 )5 CO

= 15 N label, 98%

n

(117)

4. Synthesis of [15N]labelled acetamide and acetonitrile

15N-labelled acetonitrile has been usually synthesized105 107 as in equations 55 58.

Ł	Ł		Ł
MeI C KC N /NaC N ! MeC N					(88		95% yield)	55
	Ł		Ł
Me2SO4 C KC N ! MeC N					(67% yield)			56
		Ł			Ł
Ac2O C N H3 ! Ac N H2								57
Ł	P2O5	Ł
Ac N H2 ! Me C N			(34		47% yield)			58

The first two methods105,106 require the use of the rather expensive KC15N or NaC15N. In the third approach107 the relatively inexpensive 15NH3 or 15NH4Cl are the starting isotope compounds. The rather low yield in two-step reactions 57 and 58 has been improved108 by employing 2,2,2-trifluoroethyl acetate for the reaction with 15NH4OH (equations 59 and 60).

AcOCH2CF3 C 15NH4OH ! Ac15NH2 C CF3CH2OH C H2O			59
(85% yield) m.p. 81.5		82 °C
Ac15NH2 C P2O5 ! MeC15N 75% step yield, 64% overall yield			60

III. SYNTHESIS AND USES OF COMPOUNDS CONTAINING C=C, C=O OR CN

GROUPS LABELLED WITH TRITIUM

A. Compounds Labelled with Tritium

1. Synthesis of [ 3H]-labelled trans-4-hydroxycrotonic acid (THCA-[2,3-3H]) (119)

119, identified in the central nervous system of mammalians109, and interacting with the specific GHB (4-hydroxybutyrate) biological targets110, has been tritium labelled111

944	Mieczysław Ziełinski´ and Marianna Kanska´

at the 2,3-positions as shown in equation 61.

T

T

HC

CCOOEt

1. n-BuLi

HOOCC

CCOOEt T2 , 5 % Pd / BaSO4

2. CO2

HOOC

COOEt

A lCl3

(61)

HOCH2

T

HOCH2

T

HOOC

T

1. Hydrolysis

1. SOCl2 / Et2 O

2. Separations

2. NaBH4

T

COOH

T

COOEt

T

COOEt

(119)

sp. activity 45 Ci/mmole, rad. purity 97%

O

O

NCH2 C

CCOOH

CH2 N2 / ether

NCH2 C

CCOOMe

O

O

RhCl(PPh3 )3 / T2

O

T

COOMe

NCH2

T +

T

T +

CT2 CT2 COOMe

O

COOMe

0.5M HCl

A cOH / H2 O

O

(62)

T

COOH

NCH2

T +

T

T +

CT2 CT2 COOH

O

COOH

2. Ion Exchange

1. 30 % EtNH2 / abs. EtOH

T

COO−

T

T

+

+

+

+

+

H3 NCH2 (CT2 )2 COO−

COO−

H3 NCH2

T

H3 NCH2

(121) 7% yield

(122) 7% yield

(120)

7% yield

sp. act. 52.6 Ci / mmol

sp. act. 55.8 Ci / mmol

sp. act. 83.3 Ci / mmol

r. purity 91% (TLC)

r.purity 88% (TLC)

r.purity 48% (TLC)

+ impurities (14% yield)

17. Syntheses and uses of isotopically labelled compounds

945

2. Synthesis of tritiated E- and Z-4-aminobut-2-enoic acids

The title unsaturated 4-aminobut-2-enoic acids, 121 and 122, usually referred to as TACA (trans-aminocrotonic acid) and as CACA (cis-aminocrotonic acid), exhibiting significant pharmacological activities with respect to GABA, 120, A and B receptors112,113, have been synthesized114 from methyl 4-N-phthalimidobut-2-ynoate by catalytic hydrogeneration with tritium gas in the presence of tris (triphenylphosphine)rhodium(I) chloride (equation 62). The HPLC separation of [3H]-E- and [3H]-Z-isomers as well as of tritiated 4-aminobutanoic acid (GABA) have been described114.

3. Synthesis of sphingosines tritium labelled at the 3-position

C18-Sphingosine [(2S,3R,4E)-2-amino-4-octadecen-1,3-diol], a constituent of the plasma membrane of vertebrates115, has been tritium labelled at the 3-position for the investigation of its biological function116 (equation 63). Reduction of the keto derivatives 123 with [3H]NaBH4 and subsequent conversion of the azido group into the amino group by a Staudinger reaction provided stereoselectively the tritiated D-erythro- and L-threo- sphingosines 124A, 124B and 125A, 125B respectively.

N3
										n = 7, 13, 19
HOCH2 CHCHCH									CHCnH2 n + 1
			OH
DDQ					Benzene, RT
	N3
										n = 7, 13, 19
HOCH2 CHCCH									CHCnH2 n + 1
(123)				O

NaB[3 H] Diglyme

4

(63)

N3

N3

n = 7, 13

HOCH2 CHCCH

CHCnH2 n + 1

HOCH2 CHCCH

CHCnH2 n + 1

T

OH

HO

T

PPh3 , H2 O, THF, RT

PPh3 , H2 O, THF, RT

NH3

NH3

HOCH2 CHCCH

CHCnH2 n + 1

HOCH2 CHCCH

CHCnH2 n + 1

n = 7, 13

T

OH

OH

T

(124A, 124B) D-erythro-series

(125A, 125B) L-threo-series

946	Mieczysław Ziełinski´ and Marianna Kanska´

4. Synthesis of (2S ,3R,4E )-2-amino-4-octadecene-1,3-diol-1-3H

It has been suggested117 119 that the sphingosine, 126, N,N-dimethylsphingosine, 127, and N,N,N-trimethylsphingosine, 128 might have a pharmacological use for the prevention of tumor growth and other pathological processes, since they have been shown to be the potent modulators of protein kinase C (PK-C)119,120. Tritium has therefore been introduced119 into their 1-position with complete retention of the original stereochemistry, employing regiospecific oxidation of the primary hydroxy group followed by reduction

with NaB3H4 (equation 64).

NHBoc

126	Boc2 O
		HOCH2 CHCHCH
		OH

NHBoc

O CHCHCHCH CHR1

OSiMe3

NHBoc

CHR1

Me3 SiCl, Py

CHR1

R2OCH2 CHCHCH

Me3 SiNHSiMe3

OSiMe3

reagent

R2 = SiMe3 , or H

Collins

NHBoc

NaB2 H4 / NaB3 H4

CHR1

HOCHCHCHCH

R3 H

R3 = 2 H or 3 H

NH2

CF3

COOH

(64)

NMe2

CH

HCHO, NaBH3 CN

CH

−

+

MeI

X

NMe3

CHR1

HOCHCHCHCH

R3

OH

R3 = 3 H, sp. act. 97 mCi / mmol, r. purity 97%

R1 =

C13 H2 7;

Boc =

COOCMe3

X = I or Cl

+

NR2

NMe3

HOCH2 CHCHCH

CHC13H27

HOCH2 CH

OH

(126)

R = H, sphingosine

(128) N,N,N-trimethylsphingosine

(127)

R = Me, N,N-dimethylsphingosine

17. Syntheses and uses of isotopically labelled compounds

947

5. Synthesis of tritium-labelled aminowarfarin methyl ketal regioisomers

The anticoagulant drug, warfarin [4-hydroxy-3-(3-oxo-1-phenylbutyl)-2H-1-benzo- pyran-2-one], 129, a useful tool for the study of the cytochrome P450 superfamily of enzymes121, has been tritium labelled122 for defining the nature of the substrate-binding sites of the enzymes. 6-Bromo-40 -nitro-, 130, 40 -bromo-6-nitro-, 131, 40-bromo-7-nitro-, 132 and 40-bromo-8-nitrowarfarin, 133, have been subjected to catalytic tritiation to produce the tritium-labelled aminowarfarin methyl ketals (equation 65). Tritiation of 5 mg of an equal mixture of 130, 131, 132 and 133 gave a product containing 200 mCi of tritium after removal of labile tritium. These compounds can be directly converted to the tritium-labelled ring-opened azidowarfarins via diazotization and azide substitution. All four azido compounds inactivate P4501A1, when photoactivated in its presence122.

O2 N

OH

O

(129)

Me OMe

O

O

O

Br

(65)

10 % Pd / C, D2 or T2

dioxane, Et3 N, 1 h		Me	OMe
		O
H2 N
		O	O			D(T)
O			Me		OMe
			O	(11)
R1	(6)				(9)
2	(7)	(8)	O		O	(4 ′) R4
R

R3

(130)R1 = Br, R4 = NO2 , R2 = R3 = H

(131)R4 = Br, R1 = NO2 , R2 = R3 = H

(132)R4 = Br, R2 = NO2 , R1 = R3 = H

(133)R4 = Br, R3 = NO2 , R1 = R3 = H

948	Mieczysław Ziełinski´ and Marianna Kanska´

6. Synthesis of [ 3H]cyfluthrin

Cyfluthrin, 134, a synthetic insecticide123 possessing three chiral C-atoms (1,3 and ˛), has been synthesized124 starting with bromocyfluthrin, 135, as shown in equation 66. For distribution and biotransformation studies in tse-tse files, 134 was diluted to a specific activity of 1.0 mCi/ml.

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

Me Me

(1)	(α)
O

(3)

O CN

Column separation of racemates

Me Me

O

trans

O CN

3 H2 / Pd / CaCO3 , Et3 N

Me Me

O

trans

O CN

epimerization in EtOH in position α

Me Me

O

F

C6 H4 Br-p

O

(135)(racemates I, II, III and IV)

F

C6 H4 Br-p

O

(136)racemate IV

(66)

F

C6 H4 3 H-p

O

racemate IV

F

C6 H4 3 H-p

O

OCN

(134)mixture of racemates III and IV