Patai S., Rappoport Z. 1997 The chemistry of functional groups. The chemistry of dienes and polyenes. V. 1 / 0775 867

18. Syntheses and uses of isotopically labelled dienes and polyenes

815

OR1

COOR2

3 H

N

OPh

NH

DMF

R1O

3 H

OR1

TBDMSCI

R1 = THP; R2 = H

OR1

COOMe

R1 = THP; R2 = Me

3 H

R1 = H; R2 = Me

1. DMSO / (CF3 COO)2 / CH2 Cl2

OPh

R2 O

2. Et3 N

3

3

H

OR

O

COOMe

R1 = H; R2 = R3 = TBDMS

R1 = R3 = H, R2 = TBDMS

3 H

R1 = R2 = R3 =TBDMS

OPh

TDMSO

3 H

OTBDMS

O

COOMe

48% HF

MeCN

3 H

OPh

HO

3 H

OH

(113)

43 continued

CHO

COOMe

9 steps

OSiMe2 Bu-t

17

18

OTHP

OH

OH

(44)

COOMe

(118)

T2 , (5 Ci), 2.5 h, RT

3 H

(PPh3 )3 RhCl, benzene / c-hexane

OH

OH

3 H

(116)

816		Mieczyslaw Zielinski´				and Marianna Kanska´
							COOMe
				8 steps
OH	Me						15S
								19	20
					OH		OH	Me
							(119)
									(45)
				COOMe		T2 / (10 Ci), RT, 3.5 h
							(Ph3 P)3 RhCl/ benzene / c-hexane
						3 H
			15S	17S
	OH		OH	Me		3 H
		(117) specific activity 50 Ci mmol−1
		HO	9	8	6	5
							COOH
				12	14
			O			OH
					(120)
		HO	9	8	6	5
							COOH
				12	14
			O			O
					(121)
		HO	9	8	6	5
							COOH
				12	14
			OH			OH

(122)

	18. Syntheses and uses of isotopically labelled dienes and polyenes					817
	9	8	6	5	COOH
		12	14
		O		OH
				(123)
	9	8	6	5	COOH
		12	14
		O		OH
				(124)
				R	O
					O
					O
					O
				O	O
	O
Me	O			HO
					O
	R	OH			O
(125)	R = CHTOH. 32% yield,			(126)	R = T, specific activity 130 mCi mmol−1,
	specific activity 266 mCi mmol−1				4% yield
(127)	R = CH2 OH			(129)	R = OH
(128)	R = CHO			(130)	R = OSO2 Me

4. Synthesis of tritium-labelled [15-3H]-verrucarol, 125, and [16-3H]-verrucarin A, 126

The naturally occurring mycotoxins, 125 and 126, produced mainly by fungi99 and implicated in the variety of toxicoses in man and animals99,100, have been tritium labelled101 (equations 46 and 47) for use in toxicology metabolism and pharmacokinetic studies. Position 15 in verrucarol and position 16 in verrucarin A have been tritiumlabelled, because they should not suffer from the loss of labelling protons during the

818				Mieczyslaw					Zielinski´ and Marianna Kanska´
metabolic studies in animals.
127		RuCl2 (Ph3	P)3		128			[3 H]NaBH4 , THF, RT			125	(46)
										overnight
129		MeSO2 Cl					130		[3 H]NaBH4 , 200 mCi, specific activity 11.4 Ci mmol−1			126 (47)
	Et3 N / CH2 Cl2 , 0 °C										+
										CH2 Cl2 , C16 H3 3 P(C4 H9 )3 Br−

5. Synthesis of tritium-labelled ciprostene

The tritium-labelled title compound, (U-3H)-61,431, 131, has been synthesized102 by treating the free acid with methyl iodide and diisopropylethylamine, reaction of the U- 61,431 methyl ester with t-butyldimethylsilyl chloride, separation of the 11-O-silyl and 15-O-silyl derivatives by column chromatography, oxidation of the 15-t-butyldimethylsilyl ether, methyl ester to 11-keto derivative with chromium trioxide and stereoselective reduction of the 11-keto group with sodium borotritide, to give the 11-˛-hydroxy epimer. Deprotection of the (U-3H)-15-silyl methyl ester with Bu4NF, followed by washing out the labile tritium by aqueous KOH/MeOH, gave (11-3H)-U-61, 431, which after semi-preparative HPLC has been injected subcutaneously into rats. During the first 24 h about 40% of dose radioactivity was found in the urine, and about 50% of dose in faeces 72 h after dosing. Less than 1% of tritiated water were excreted in urine, faeces and expired air.

HOOC

Me

	3 H	OH
	OH
	(131)
6. Synthesis of tritium-labelled fluorescent derivatives of prostaglandins
Tritium-labelled	PGE1 (50 Ci mmol 1),	PGF2˛ (150 Ci mmol 1)	and PGE2
(180 Ci mmol 1)	have been converted103	into 1,5-DNS derivative,	1,5-DNS-1-

(dimethylamino)-5-naphthalenesulphonic acid hydrate, Me2NC10H5SO3HžxH2O, a highly sensitive fluorescent probe for proteins104 106. The doubly labelled [3H]-DNS-PGs could therefore be used as a radioactive fluorescent probe for liquid receptor interactions in biological membranes and also for determination of the molar radioactivity isotopically labelled PGs, when the amount of the labelled compound is very small.

D. Synthesis of Limonene

1. Synthesis of (4S)-( )-[9-3H]-limonene

The title compound, 132, (4S)-[9-3H]-1-methyl-4-(10 -methylethenyl)cyclohexene, has been synthesized107 from (10 S,2R,S)-2-(40 -methylcyclohex-30-enyl)propanal [(4S,8R,S)- ( )-1-p-menthen-9-al, 133], via a route shown in equation 48 in 55% overall yield

18. Syntheses and uses of isotopically labelled dienes and polyenes

819

and improved enantiomeric purity (72% ee, compared with the literature method108 of 38% ee). The radioactive (4S)-( )-limonene, 132, was needed as substrate in the course of studies of the biosynthesis107 of carvone in Mentha spicata (spearmint).

(7) Me

(1)

(6)		(2)	i-PrOH, NaB3 H4 (925 MBq)
(5) (4)		(3)	1. 2 h at 0°C					C(9)3HHOH
			2. 1 h at RT
(8)	(9)		3. Work-up
(10) Me		CHO						TsCl	DMA P / CH2 Cl2
(133)				NaI / acetone						(48)
			C(9)3HHI					C(9)3HHOTs
				reflux at 70	°C, 17 h
				DBU	Me

Me C3 HH

[9-3H]-(132)

specific activity 629 MBq mmol−1

E. Synthesis of Dienes by Catalytic and Radiochemical Methods

1. Synthesis of tritium-labelled brefeldin-A by catalytic isotope exchange with tritium gas

The title compound BFA, 134, has a profound effect on the Golgi apparatus and can alter the membrane traffic. Tritium-labelled 134 should help to understand its biological action. 134 has been labelled with tritium109 at positions ˛/ˇ to both double bonds (whereas the

	OH		O
	(5)			O
HO		(3)	(1)	Me
				(15)
(7)				H
(8)
	(10)	(12)		(14)
	(134)	Brefeldin A

820

Mieczyslaw

Zielinski´ and Marianna Kanska´

labelling on the double bond was of minor importance) by hydrogen isotope exchange of 134 with tritium gas (T2) in 1,4-dioxane over a commercial palladium catalyst supported on diatomaceous earth (5% metallic weight). The addition of air in the gas phase increased the catalytic activity. The exchange has been considerably enhanced when the air/T2 ratio was about four. The specific activities of 134 were up to 2.8 Ci mmol 1. Two mechanisms for tritium incorporation into 134, involving two different adsorbed species, ‘ ’, 135, and ‘ allylic’, 136, on the catalyst surface have been proposed110 (equations 49 and 50, respectively) and discussed109. The investigation of all factors governing the exchange reaction should result in obtaining higher tritium specific activities of 134.

OH

OH

(4)

H

(3)	(2)	T

+ T

OH

(4)

H

(2)

− H

C.S.

C.S. = catalytic site

(10)(12)

(13)

(10)(12)

(13)

C . S .

(10)(12)

(11) (13)

C . S . (136)

C. S.

−H

+X

−H

OH

(4)

C. S.

(135)

(12)

(13)

	X
(10) (11)	X

+X

(11) (13)

(10) (12)

C . S . (136)

+X +X

(10)(13)

(11)(12)

X = H or T C . S .

(49)

(50)

	18. Syntheses and uses of isotopically labelled dienes and polyenes			821
2. Synthesis of simple seven-membered ring compounds labelled with tritium
The	following 14 seven-membered ring compounds, increasing in complexity
from	cycloheptane	to complicated benzodiazepine systems, have	been	labelled
with tritium111 using ‘activated tritium’ (AcT method) employing			a microwave
power	generator112,	‘adsorbed tritium’ at RT (AdT method113) and high-temperature

tritium ion (‘HTI’ method111): cycloheptane, 137, 1,3-cycloheptadiene, 138, 1,3,5- cycloheptatriene, 139, 2-cyclohepten-1-one, 140, (t)-3,3,5-trimethylhexahydroazepine, 141, 2-oxohexamethyleneimine (caprolactam), 142, 1-aza-2-methoxy-1-cycloheptene, 143, 1,4-diazacycloheptane (homopiperazine), 144, azulene, 145, 1-benzosuberone, 146, 1,8-diazabicyclo-[5.4.0]undec-7-ene, 147, 5H-dibenzo[b,f]azepine (iminostilbene), 148, trans-10,11-dibromodibenzosuberone, 149, and 8-chloro-11-(4-methyl-1-piperazinyl)5H- dibenzo[b,e]diazepine (clozepine), 150.

(137) 10.5 mCi yield,	(138) 8.6 mCi yield			(139) 6.8 mCi yield
specific activity 31.8 mCi mmol−1	specific activity 8.9 mCi mmol−1			specific activity 17 mCi mmol−1
	Me		Me	O
				NH
O	Me		NH
(140) 134 mCi yield	(141)	2.4 mCi yield		(142) 166 mCi yield
specific activity 157 mCi mmol−1	specific activity 16 mCi mmol−1			specific activity 107 mCi mmol−1
OMe	HN
N			NH
(143) 299 mCi yield	(144)	32 mCi yield		(145) 48 mCi yield
specific activity 428 mCi mmol−1	specific activity 48 mCi mmol−1			specific activity 185 mCi mmol−1
O
			N
			N	NH
(146) 172 mCi yield	(147)		101 mCi yield	(148) 117 mCi yield
specific activity 1833 mCi mmol−1	specific activity 151 mCi mmol−1 specific activity 238 mCi mmol−1

Many biologically active substances and neuroleptic drugs have a seven-membered ring in their structure. Benzodizapines of extremely high specific activity used in receptor binding studies are isotopically labelled by synthesis114. The specific activities of compounds 137 150 are sufficiently high for in vitro metabolic and radiotracer studies.

822	Mieczyslaw Zielinski´	and Marianna Kanska´
			Me
Br	Br		N
			N
		Cl	N
	O		NH
(149)	17 mCi yield	(150)	2 mCi yield
specific activity 43 mCi mmol−1		specific activity 562 mCi mmol−1

The distribution of tritium in compounds 137 150 can be determined by tritium NMR spectroscopy without chemical manipulations115. The structure retention index relationship (SR IR)116 has been used for identification of unknown radioactive peaks and to differentiate by-products from radioimpurities from extraneous sources.

F. Tritium Isotope Effects in Synthesis of Polyenes

1. Synthesis of [6-2H] and [6-3H] fecapentaene

Fecapentaene 151, a potent mutagen, potential inducer of colon cancer, first isolated from human feces117,118, has been deuterium and tritium labelled119 by exchange of the ˛-protons of (E,-E)-2,4-heptadienyldiphenylphosphine oxide, 152, with 2H2O or 3H2O, followed by Wittig Horner condensation with aldehyde 153, and deprotection of the silylated derivative 154 with fluoride (equation 51), 151 is used in the study of its interactions with DNA119.

The maximum specific activity of tritium120 (I1/2 D 12.33 years) equals 9664 Ci g 1. Tritium specific activity of the product 151 [3H] indicates a slightly higher retention of 3H relative to 1H in the coupling second step. No tritium, deuterium and carbon-14 KIE and exchange systematic study of the mechanism of the Wittig Horner coupling reaction119 has been carried out. The determined specific activities of the ˛-tritiated 2,4-heptadienyldiphenylphosphine oxide 152 (0.41 mCi mmol 1) and of the product 151 (equation 52) (0.24 mCi mmol 1) indicate a rather small intramolecular C 1H/C 3H KIE in the rupture of one of the two ˛-carbon hydrogen bonds in the coupling reaction above. This is characteristic for highly asymmetrical transition states if the rupture of the C H bond takes place in the rate-determining step and the double C 5 DC 6 bond formation occurs in the subsequent fast product 154 formation step. We assume also that silylated derivative 154 and product 151 are tritium-labelled in non-labile C 6 position. Silylated derivative 153 tritium-labelled at the terminal keto group has not been investigated. 14C KIE have also not been studied. The interpretation of the small kH/kT value of 1.4 should therefore be postponed. We note that no yield of 154 with respect to the tritiated precursor

152, which is needed for intermolecular 3H KIE estimation, was given.

18. Syntheses and uses of isotopically labelled dienes and polyenes

823

(51)

	1H	k(1H)	C			3 H
		−1H					(52)
C						k(1H) k(3H) 1.412
		k(3 H)
	3 H
			C			1H

−3H

2. Synthesis of [3-3H] squalene and [3-3 H]-2,3-oxidosqualene

[3-3H]Squalene, 155, and [3-3H]-2,3-oxidosqualene, 156, the key compounds in studies of the biosynthesis of sterols121, have been obtained122 according to the route shown in equation 53, which involves the modified Wittig reaction of [1-3H]trisnorsqualene aldehyde 157 with phosphorus ylide to give 155 or with sulphur ylide to give 156 in high radiochemical yield and high purity.

At room temperature the chemical and radiochemical yields of 155 were different. The chemical yields were in the 30 40% range, while the radiochemical, not very reproducible yields were in the 6 15% range. Cattel and coworkers122 assigned these differences to tritium isotope effect in the Wittig reaction. No correlation between the specific activity of 155 and the degree of chemical conversion of 157 into 155 has been presented. The temperature dependence of the observed secondary tritium isotope effect has also not been

824

Mieczyslaw

Zielinski´ and Marianna Kanska´

pyridinium

NaB3 H4

C H

chlorochromate

CH

Cl

MeOH

2

2

2

C HO

CHO

OH

(157)

+

−

+

−,

Me2 CHPPh3 Br

Me2 CHSPh2 BF4

NaNH2 , BuLi, THF

PhLi, THF

reflux 15 min

(53)

	H
	O
H
(155) [3-3 H] squalene, 84% radiochemical yield	(156) 77% chemical yield
H = 3 H	26 mCi, specific activity 1.9 Ci mmol−1

studied. The C Ł H bond at the aldehyde carbon is not broken in the course of Wittig reaction but the vibrational motion of the aldehyde hydrogen should be less constrained in the transition state corresponding to formation of 155 from 157.

IV. SYNTHESIS AND USES OF DIENES AND POLYENES LABELLED WITH

RADIOISOTOPES OF CARBON

A. Synthesis and Uses of Dienes and Polyenes Labelled with Carbon-11

1. Remote radiosynthesis of 1-[14C]polyhomoallylic fatty acids

1-[11C]arachidonic acid, 158a-11C and 1-[11C]docosahexaenoic acid, 158b-11C, have been prepared123 applying a retro-synthesis involving a radical decarboxylation of N-hydroxypyridine-2-thione esters124 of both arachidonic and docosahexaenoic acid, formation of the polyhomoallylic magnesium bromide from the corresponding (all-Z)- 1-bromononadeca-4,7,10,13-tetraene, 159a, and (all-Z)-1-bromoheneicosa-3,6,9,12,15,18- hexaene, 159b, and subsequent carbonylation of the Grignard reagents with [11C]CO2

(equation 54). The final radiochemical purities of 158a-11C and 158b-11C were in excess of 95% by radio-HPLC. 158a-11C and 158b-11C were used123,125 for in vivo evaluation

of regional brain phospholipid metabolism by PET. Both 158a-11C and 158b-11C are