Bloconlugate Chem. IQQI, 2, 337-341
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Photolysis of 3-Aryl-3-(trifluoromethyl)diazirines:A Caveat Regarding Their Use in Photoaffinity Probes Matthew Platz,'J Atnaf S. Admasu,+ Stefan Kwiatkowski,* Peter J. Cracker,* Nobuyuki Imai? and David S. Watt'J Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, and Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506. Received May 6, 1991 The photolysis of 3-(4-tolyl)-3-(trifluoromethyl)diazirine in the presence of benzene, methanol, carbon tetrachloride, cyclohexane, triethylsilane, or diethylamine led to photoproducts consistent with the intermediacy of a singlet carbene. In the case of diethylamine, the photoinsertion into the N-H bond of diethylamine produced the expected adduct, l-(diethylamino)-2,2,2-trifluoro-l-(4-tolyl)ethane. However, the base-catalyzed elimination of hydrogen fluoride from this adduct afforded an enamine, a-(diethylamino)-8,~-difluoro-4-methylstyrene, and the subsequent hydrolysis of this enamine furnished diethylamine and 2,2-difluoro-l-(4-tolyl)ethanone.This elimination and hydrolysis sequence effectively reversed the photoinsertion process. A similar photoinsertion and hydrolysis process using 3-(4-noctylphenyl)-3-(trifluoromethyl)diazirine also produced 2,2-difluoro-l-(4-n-octylphenyl)ethanone in modest yield. These results suggest that the photoinsertion products from 3-aryl-3-(trifluoromethyl)diazirines in biological systems may suffer similar fates limiting, in part, their utility in obtaining primary sequence data.
INTRODUCTION Interest in photoaffinity cross-linking reagents for elucidating the structure of receptors led to various probes that incorporate photoactive aryl azides (1-4), perfluorinated azides (5-1 O), and 3-aryl-3-(trifluoromethyl)diazirines (11-27). The diazirine category of photoactive probes has enjoyed considerable popularity as a result of a general impression that the photolysis of a 3-aryl-3-(trifluoromethy1)diazirine affords a reactive carbene intermediate and that the insertion of the carbene establishes an irreversible, covalent cross-link to a variety of amino acid residues within the target protein. In contrast, recent evidence suggested that the photolysis of the phenyl azide category of probes generated a less reactive, electrophilic dehydroazepine that selectivelyscavenged for nucleophilic Lys or Cys residues. It was expected, therefore, that 3-aryl3-(trifluoromethy1)diazirineswould result in more efficient cross-linking than their phenyl azide counterparts and would afford covalent adducts that would tolerate the subsequent digestion, purification, and sequencing process. Despite these advantages, relatively few studies using 3-aryl-3-(trifluoromethyl)diazirineshave led to primary sequence data. Difficulties encountered in the biochemical application of photoaffinity probes bearing the 3-aryl-3(trifluoromethy1)diazirine group to the acquisition of primary sequence data prompted this study of the distribution and stability of the photoproducts of two model systems, 3-(4-tolyl)-3-(trifluoromethyl)diazirine(la) and 3-(4-n-octyl)-3-(trifluoromethyl)diazirine (lb). EXPERIMENTAL PROCEDURES 3-(4-Tolyl)-3-(trifluoromethyl)diazirine(la) and 3-(4-n-0ctyl)-3-(trifluoromethyl)diazirine (lb). Literature procedures (28-30) were repeated with some modifications as shown in Scheme I and are described below. 2,2,2-Trifluoro-1-(4-tolyl)ethanone (loa). To 1.4 g (200 mmol) of lithium in 100 mL of anhydrous Et20 at 25
* Authors to whom correspondence should be addressed.
+ The
Ohio State University.
* University of Kentucky.
1043-180219 112902-0337$02.50/0
Scheme I.. Synthesis of 3-Aryl-3-(trifluoromethyl)diazirines
9
a
10
NOH 11
Series a, R = CHs; series b, R = n-CJ41.r. Reagent legend: a. Li. EkO in the case of 10a and n-BuLi. EtnO. -78 "C in the case of lob; b, CFaC02Et; c, H2NOH; d, MsCl, EtiN; e, NHs, -78 "C; f, AgnO. "C was added 13.0mL (105 mmol) of 4-bromotoluene (9a). After a 15-min induction period, the solution refluxed as a result of the slightly exothermic reaction. After stirring for 2 h, a Nz flow was started, and the reaction was cooled to -78 "C. To this 4-tolyllithium solution was added 13.0 mL (113 mmol) of ethyl trifluoroacetate via syringe over a 10-min period. The solution was allowed to warm to 25 "C and was stirred for a total of 12 h. The reaction was quenched by adding 10 mL of saturated NH4Cl solution and 5 mL of water. The Et20 solution was separated, washed successivelywith half-saturated NH4C1and water, and dried over anhydrous MgS04. The solution was concentrated to afford 19 g of crude 10a as a dark orange liquid. lH NMR indicated that this product was a 57:43 mixture of unreacted 9a and the desired product loa: IR (TF) 1710 (C=O) cm-l; lH NMR (CDC13) 6 2.45 (s, 3, CHd, 7.34 and 7.96 (2 d, J = 8.6 Hz, 4, ArH). This crude mixture was used in the next reaction without further purification. 2,2,2-Trifluoro-l-(4-tolyl)ethanone Oxime (lla). To the crude mixture from the previous reaction, which was calculated to contain ca. 10 g (53 mmol) of loa,was added 11.1g (159 mmol) of hydroxylamine hydrochloride and 6.39 g (160 mmol) of sodium hydroxide in 200 mL of absolute EtOH. The mixture was refluxed for 21 h and cooled. Most of the ethanol was removed under reduced 0 1991 American Chemical Society
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HC1. The solution was stirred for 30 min. The product pressure, and the residue was diluted with water. The was extracted with ether and the ether solution was washed aqueous solution was acidified to pH 1 with 3 M HC1 with brine and dried over anhydrous MgS04. The solution solution and extracted with EtzO. The Et20 solution was was partially concentrated on a rotary evaporator. The washed with brine and dried over anhydrous MgS04. The lH NMR spectrum of this product displayed a signal at solution was concentrated and the product was purified 6 6.28 (t, JHF = 53.6 Hz, 1, CHFz) consistent with the by flash chromatography on silica gel using 1:19 EtOAcpresence of 6a. Isolation of 6a in a pure state was hampered hexane to afford 11.1 g (53% for two steps) of lla as an by its volatility, and a semicarbazone derivative failed to E,Z mixture that was a pale orange liquid: IR (TF) 3340 produce a satisfactory combustion analysis. (br, OH), 1705 (C=N) cm-1; 1H NMR (CDCl3) 6 2.38 (9, 3, CH3), 7.18-7.50 (m, 4, ArH), 9.52 (br s, 1, OH). 2,2,2-Trifluoro-1-(4-n-octylphenyl)ethanone (lob). 2,2,2-Trifluoro-1-(4-tolyl)ethanone O-(MethylsulTo 9.0 mL (23 mmol, 2.1 equiv) of 2.5 M n-BuLi in hexane fony1)oxime (12a). To 11.1 g (54.5 mmol) of lla in 200 was added over a 10-min period 2.5 mL (11 mmol, 1.0 mL of anhydrous THF1 at 0 "C was added 6.3 mL (81 equiv) of l-bromo-4-n-octylbenzene (9b) in 55 mL of mmol) of MsC1. To this solution was added dropwise a anhydrous Et20 a t -78 "C under a Nz atmosphere. The solution of 12 mL (88 mmol) of Et3N in 40mL of anhydrous temperature was allowed to rise to 0 "C over a 5-hperiod. THF over a 15-min period. The solution was stirred for The solution was cooled to -78 "C, and 4.0 mL (34 mmol, an additional 15 min, and the ice-water bath was removed. 3.1 equiv) of ethyl trifluoroacetate was added. The solution The solution was stirred for an additional 1 h at 25 "C. was allowed to stir for 13 h, during which time the temThe THF was removed under reduced pressure. The perature was allowed to rise to 25 "C. The reaction was residue was dissolved in water and extracted with EtzO. quenched with water, and the product was extracted with The Et20 solution was washed with brine and dried over Eh0. The ethereal solutions were combined, washed with anhydrous MgS04. The solution was concentrated to brine, and dried over anhydrous MgSO4. The solution afford 14.3 g (93%) of crude product that was used directly was concentrated, and the crude product was chromatoin the next reaction. A small portion was purified by graphed on silica gel using hexane to afford 1.88 g (61 5%) column chromatography on silica gel using 1:9 EtOAcof 10b (38-41) as a clear, colorless liquid: IR (TF) 2965, hexane and by recrystallization from EtOAc-hexane to 2940,2865,1711 (CO), 1605,1206,1176,1148,942cm-'; give 12a as white needles: mp 80.5-82.0 "C; IR (KBr) 'H NMR (CDC13) 6 0.88 (t, J = 6.2 Hz, 3, CH3), 1.27 (br 3035,1610,1373,1200,1187cm-l; lH NMR (CDCl3) 6 2.42 s, 10 (CH2)5), 1.64 (t, J = 7.3 Hz, 2, ArCHzCHz), 2.70 (t, (9, 3, ArCH3), 3.25 (s, 3, OS02CH3), 7.31 and 7.42 (2 d , J J = 7.7 Hz, 2, ArCHz), 7.35 and 8.00 (2 d , J = 8.3 Hz, 4, = 8 Hz, 4, ArH). Anal. Calcd for C I O H ~ O F ~ N O C,~42.71; S: ArH). Anal. Calcd for C I ~ H Z I F ~ O C,: 67.12; H, 7.39. H, 3.58. Found: C, 42.73; H, 3.58. Found: C, 67.21; H, 7.43. 3-(4-Tolyl)-3-(trifluoromethyl)diaziridine(13a). To 2,2,2-Trifluoro- 1-(4-n-octylpheny1)ethanone Oxime 14.1 g (50 mmol) of 12a in a flask cooled to -78 "C and (11b). The procedure described in the preparation of 1la equipped with a dry ice-acetone condenser was introduced was repeated with 1.88 g (6.57 mmol, 1.0 equiv) of lob, ca. 150 mL of liquid ammonia. The solution was stirred 1.37 g (19.7 mmol, 3.00 equiv) of hydroxylamine hydrofor 6 h, the dry ice-acetone bath was removed, and the chloride, and 0.828 g (20.7 mmol, 3.15 equiv) of NaOH to liquid ammonia was allowed to evaporate. The residue afford, after chromatography on silica gel using CHC13, was dissolved in water and extracted with EtzO. The 1.17 g (59%)of l l b as an E,Z mixture that was a clear, aqueous layer was extracted with additional EtzO. The pale yellow oil. A sample for analysis was obtained by Et20 solutions were combined, washed with brine, and recrystallization a t -20 "C from hexane: mp 32-34 "C; IR dried over anhydrous NazS04. The crude product (13a) (KBr) 3320 (OH), 2960,2930,2860,1178,1138,1010,963 was used in the next reaction without further purification: cm-l; lH NMR (CDC13) 6 0.88 (t, J = 6.3 Hz, 3, CH3), 1.27 mp 44-46 "C (from hexane at -20 "C) [lit. (30) mp 45-46 (br s, 10, (CHZ)~), 1.52-1.73 (m, 2, ArCH&Hz), 2.65 (t,J "C]; IR (KBr) 3200 (NH), 1395 cm-l; lH NMR (CDCl3) 6 = 7.8Hz,2,ArCH2),7.30and7.49(2d,J= 8.2Hz,4,ArH), 2.20and 2.77 ( 2 d , J = ~ H z , ~ , H N N H ) , ~ . ~ ~ ( s , 9.24 ~ , A(9,~1,COH). H ~ )Anal. , Calcd for C ~ ~ H Z ~ F ~C,N63.77; O: 7.23 and 7.50 (2 d, J = 8 Hz, 4, ArH). H, 7.36. Found: C, 63.82; H, 7.39. 3-(4-Tolyl)-3-(trifluoromethyl)diazirine(la). To 2,2,2-Trifluoro-l-(4-n-octylphenyl)ethanone 07.7 g (38 mmol) of 13a in 100 mL of Et20 was added 15.6 (Methylsulfony1)oxime (12b). The procedure described g (67 mmol) of freshly prepared AgzO in portions over 1 for the preparation of 12a was repeated with 1.12 g (3.72 h. The mixture was stirred for an additional 2 h and mmol, 1.0 equiv) of llb, 0.45 mL (5.8mmol, 1.6 equiv) of filtered through a bed of Celite. The filtrate was conMsC1, and 0.80 mL (5.7 mmol, 1.5 equiv) of EtsN to afford, centrated, and the crude product was chromatographed after chromatography on silica gel using 2:3 hexaneCHCl3, on silica gel using 1:19 EtOAc-hexane to afford 4.3 g (56% ' ) 943 mg (67 % ) of 12b as an off-white, waxlike solid: mp of la as a uolatile, light yellow liquid: IR (TF) 3050,2935, 39-41 "C; IR (KBr) 2955, 2925, 2855, 1372, 1184, 1140 1611,1518,1347,1242,1229,1214,1185,1155,1054,939, cm-'; 'H NMR (CDCls)6 0.88 (t, J = 6.2 Hz, 3, CHs), 1.27 808, 730 cm-I; UV (cyclohexane) A,, 361 nm (c = 346); (br s, 10, (CHZ)~), 1.53-1.74 (m, 2, ArCHzCHZ), 2.66 (t,J 'H NMR (CDCl3) 6 2.36 (s,3, ArCH3), 7.09 and 7.21 (2 d, = 7.7 Hz, 2, ArCHz), 3.26 ( 8 , 3, CHsSOz), 7.31 and 7.44 (2 J = 8 and 1 Hz, 4, ArH). d, J = 8.3 Hz, 4, ArH). Anal. Calcd for C17H24FsNOsS: 2,2-Difluoro-l-(4-tolyl)ethanone (6a). A solution of C, 53.81; H, 6.38, Found: C, 53.92; H, 6.39. 56 mg (0.28 mmol) of la in 2.5 mL of diethylamine in a 3-(Trifluoromet hyl)-3- (4-n-octylpheny1)diaziri5-mm Pyrex NMR tube was degassed with nitrogen and dine (13b). The procedure described for the preparation irradiated for 16 h in a Rayonet photochemical reactor of 13a was repeated with0.90g (2.4mmol) of 12bto afford, (RPR-2537A tubes). The solution was transferred to a after chromatography on silica gel using 1:19 acetoneround-bottomed flask and was diluted with 25 mL of 1 M CHC13,610mg(84%)of 13basalightyellowoil. Asample for analysis was obtained by recrystallization at -20 "C Abbreviationsused: n-BuLi, n-butyllithium; EPR,electron from hexane to afford a cottonlike, white solid: mp 41-43 paramagnetic resonance; MsCl, methanesulfonyl chloride;PC, "C; IR (KBr) 3210 (NH), 2930,2855,1180,1142 cm-l; 'H phenylcarbene;THF, tetrahydrofuran; TTC, 4-tolyl(trifluoromethy1)carbene. NMR (CDC13) 6 0.88 (t, J = 6.5 Hz, 3, CHa), 1.27 (br s, 10,
Bioconjugate Chem., Vol. 2, No. 5, 1991 330
bAryC~~fluoromethy1)dierirines
(CH2)6), 1.51-1.72 (m, 2,ArCH&H2), 2.21 and 2.77 (2d, J = 8.6 Hz, 2,HNNH), 2.63 (t, J = 7.7Hz, 2,ArCHz), 7.23 and 7.52 (2 d, J = 8.1 Hz, 4, ArH). Anal. Calcd for C ~ ~ H B F ~C,N63.98; ~ : H, 7.72. Found: C, 63.83;H, 7.78. 3-(Trifluoromethyl)-3-(4-n-octylphenyl)diazirine (lb). The procedure described for the preparation of la was repeated with 571 mg (1.90mmol, 1.0 equiv) of 13b and 1.3 g (5.6mmol, 2.9 equiv) of freshly prepared AgzO to afford, after chromatography on silica gel using CHCl3, 460 mg (81% ) of lb as a yellow liquid: IR (TF)2965,2935, 2860,1343,1237,1182,1155,939 cm-l; UV (95% EtOH) ,,A 363 nm (e = 378);lH NMR (CDCl3) 6 0.88 (t,J = 6.3 Hz,3,CH3), 1.27 (brs, 10,(CH2)5),1.50-1.67 (m, 2,ArCHzCHz), 2.61 (t, J = 7.7 Hz, 2,ArCHz), 7.10 and 7.21 (2d, J = 8.3 Hz, 4, ArH). Anal. Calcd for C I ~ H ~ I F ~C,N ~ : 64.41;H, 7.09. Found: C, 64.36;H, 7.14. 2,2-Difluoro-l-(4-n-octylphenyl)ethanone (6b). A solution of 58 mg (0.19mmol) of la in 1.7 mL of diethylamine in a 5-mm Pyrex NMR tube was degassed with argon and irradiated for 4 h in a Rayonet photochemical reactor (RPR-3500 tubes). The solution was allowed to stand for 20 h, transferred to a round-bottomed flask, and diluted with 20 mL of 1 M HC1. The solution was stirred for 3.5 h. The product was extracted with ether and the ether solution was washed with brine and dried over anhydrous MgS04. The solution was concentrated on a rotary evaporator and chromatographed on silver nitrate impregnated silica gel preparative layer plate using 1:9 EtOAc-hexane to afford 9 mg (18%) of 6 b IR (CHCl3) 2960,2935,2855,1692,1601 cm-l; 'H NMR (CDC13)6 0.88 (t, J = 6.4 Hz, 3, (CH2)5CH3),1.20-1.30(m, 10, (cH2)5CH3), 1.52-1.76(m, 2,ArCH&H2CH2), 2.69 (t,J = 7.7 Hz, 2,ArCH&H2CH2), 6.29 (t, JHF= 53.6 Hz, 1,CHFz), 7.34 and 8.00 (2 d, J = 8.3 Hz, 4, ArH). Anal. Calcd for CleHz2F20: C, 71.62;H, 8.26. Found: C, 71.44;H, 8.31. EPR Spectroscopy. A solution of la (0.015M initial concentration) in perfluoro-2-n-butyltetrahydrofuran(Fluorochem Limited, Glossop, U.K.)was placed in a 4-mm quartz tube. It was degassed by three freeze-pump-thaw cycles and sealed under vacuum. The tube was immersed in liquid nitrogen in a Wilmad (Buena Vista, NJ) EPR dewar and irradiated with four RPR 3500bulbs (Southern New England Ultraviolet, Hamden, CT). The dewar was transferred to the cavity of a Varian (Palo Alto, CA) EPR 112 spectrometer, and the spectrum was recorded. GC-MS Studies. Samples of la (0.015 M initial concentration) in various solvents were placed in 5-mm Pyrex cells and degassed by three freeze-pump-thaw cycles and sealed under vacuum. The tubes were photolyzed at 350 nm with four Rayonet RPR 3500 bulbs for 4 h. The samples were analyzed by GC-MS immediately after the tubes were opened with a Hewlett-Packard 4021 gas chromatograph-mass spectrometer.
Table I. The Products Formed on Photolysis of la in Various Solvents at Ambient Temperature As Determined by GC-MS solvent major products trace products
WCH3 pCH3 H CF,
CHsOH
CH,O
H CF,
cc4
0 0 Q qPcH3 H CF,
i:i
+
dl 2
H CF,
WCH3 gCH3 0 CF,
Et3SiH
H
CF2
A related photolysis of 3-(4-n-octyl)-3-(trifluoromethyl)diazirine (lb)produced a similar product distribution, but only ketone 6b was fully characterized in this case. DISCUSSION
Current interest in the development of photoaffinity probes possessing 3-aryl-3-(trifluoromethyl)diazirines(1127) stems in part from the expectation that the reactive carbene intermediate, generated on photolysis of these reagents, will establish an irreversible cross-link to amino acid residues within the protein receptor. Various reports outline the synthesis of novel probes of this type (28-30) and the successful cross-linking of radiolabeled diazirine probes. However, the characterization of the photophysical states, detailed photoproduct distributions, and phoRESULTS toproduct stabilities have not been reported. The photolysis of 3-(4-tolyl)-3-(trifluoromethyl)diazirPhenylcarbene (PC)l is a rather well-characterized ine (la)in benzene, methanol, carbon tetrachloride, cyspecies having a triplet ground state as indicated by lowclohexane, triethylsilane, and diethylamine led to the temperature EPR spectroscopy (31). Nevertheless, most expected insertion or addition products as summarized in of the solution-phase chemistryof this species derives from Table I. The principal photoproducts were identified by a low-lying, readily accessible, highly reactive singlet state gas chromatography-mass spectrometry. The photolysis (32). The evidence suggests that singlet and triplet PC of la in diethylaminesolution (0.2M initial concentration) equilibrate more rapidly than either state can trap a for 4 h at 25 OC using a Rayonet RPR 3500 reactor led to neighboring hydrocarbon (33,34).The lifetime of the spinthe followingproduct distribution: 4-(2,2,2trifluoroethy1)equilibrated triplet PC in acetonitrile is ca. 1-10 ns (35). toluene (7a),l-(diethylamino)-2,2,2-trifluoro-l-(4-tolyl)The photolysis of la a t ca. 350 nm in glassy perfluoroethane (4a), cr-(diethylamino)-&(3-difluoro-4-methylsty2-n-butyltetrahydrofuran at 77 K produced an easily rene (Sa),2,2-difluoro-l-(4-tolyl)ethanone(6a)in a 3.1: discerned EPR spectrum characteristic of a triplet car1.7:6.5:1.2ratio (uncorrected), according to GC analysis. bene with ID/hcl = 0.5215 cm-1 and IE/hcl= 0.0305 cm-1
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Bloconlugete Chem., Vol. 2, No. 5, 1991
Scheme 11. Expected Triplet-State Reactions
carbene (33,37). TTC also inserted cleanly into the OH bond of methanol (a characteristic singlet carbene process), a C-C1 bond of CC4, the N-H bond of diethylamine, and the Si-H bond of triethylsilane. However, in the latter case, the adduct was not stable with respect to the loss of EtaSiF. A similar observation involving the adduct of diethylamine undergoing the loss of HF and the presence of amine functionality in a number of biological targets for which these probes might be used prompted a more detailed investigation of this instability. As shown in Scheme 111, a myriad of products emerged from a detailed study of the photolysis of la in diethylamine, in which insertion of the singlet carbene into the N-H bond of diethylamine produced the adduct l-(diethylamino)-2,2,2-trifluoro-1-(4tolyl)ethane(4a). Of particular interest was the rapid elimination of hydrogen fluoride from 4a that produced enamine 5a and a subsequent hydrolysis that furnished diethylamine and 2,2-difluoro-l-(4-tolyl)ethanone(6a). A similar elimination was noted in the case of a product formed from the insertion of a 3-aryl-3-(trifluoromethyl)diazirine into tertbutyl alcohol (29). This elimination and hydrolysis sequence effectively reversed the photoinsertion process and suggested that the use of photoaffinity probes bearing 3-aryl-3-(trifluoromethy1)diazirines may lead, in some cases, to chemically unstable photoadducts that are unlikely to survive peptide-sequencing conditions.
JyH3 .. 0F3cJycH3 -0
F3C
+
e
4
H
8
7
Scheme 111.. Photolysis of 3-Aryl-3-(trifluoromethyl)diazirines CF3
$yR..-
N=N 1
C
F
3
ACKNOWLEDGMENT
3
2
p
H NE12
R
-HF_
F2c.@R
We thank the National Institutes of Health (HD 25961) and the National Science Foundation (CHE-8814950)for their generous financial support. 4
NE12 5
4
(1) Torres, M. J., Zayas, J., and Platz, M. S. (1986) A formal CH
6
7
R 8 0
LITERATURE CITED
Series a, R = CHa; series b, R = n-CsH1.l.
(36).The zero-field parameters are very similar to those of triplet PC, and consequently, the carrier of the EPR spectrum was attributed to 4-toly(trifluoromethyl)carbene (TTC). Thus, the triplet state was identifiedas the ground state of this species. Diazirine la was photolyzed in a variety of representative solvents, and the products were analyzed by GC-MS. The results (Table I) indicated that in most solvents, it was the low-lying singlet state of the carbene which was intercepted t o give the predominant products. It was of particular interest that TTC inserted cleanly into a C-H bond of cyclohexane. There was no evidence for triplet carbene involvement because the characteristic products of hydrogen atom abstraction, shown in Scheme 11, were not observed even in trace quantities. TheCH/CD isotope effect for the singlet carbene CH insertion for TTC into cyclohexane and cyclohexane-dlz was 1.93, a value which matched that reported for singlet PC and l-naphthyl-
insertion reaction of an aryl nitrene into an alkyl CH bond. Implications for photoaffinity labeling. Tetrahedron Lett. 27,791-794. (2) Leyva, E., Platz, M. S., Persy, G., and Wirz, J. (1986) Photochemistry of phenyl azide: the role of singlet and triplet phenylnitrene as transient intermediates. J.Am. Chem.SOC. 108,3783-3790. (3) Shields, C. J., Chrisope, D. R., Schuster, G. B., Dixon, A. J., Poliakoff, M., and Turner, J. J. (1987) Photochemistry of aryl azides: Detection and characterization of a dehydroazepine by time-resolved infrared spectroscopy and flash photolysis at room temperature. J. Am. Chem. SOC.109, 4723-4726. (4) Schuster, G. B., and Liang, T.-Y. (1987) Photochemistry of 3- and 4-nitrophenyl azides: Detection and characterization of reactive intermediates. J . Am. Chem. SOC.109,7803-7810. (5) Levya, E., Munoz, D., and Platz, M. S. (1989)Photochemistry of fluorinated aryl azides in toluene solution and in frozen polycrystals. J. Org. Chem. 54, 5938-5945. ( 6 ) Young, M. J. T., and Platz, M. S. (1989) Polyfluorinated aryl azides as photoaffinity labelling reagents: The room temperature CH insertion reactions of singlet pentafluorophenyl nitrene with alkanes. Tetrahedron Lett. 30, 2199-2202. (7) Soundararajan, N., and Platz, M. (1990) Descriptive photochemistry of polyfluorinated azide derivatives of methyl benzoate. J. Org. Chem. 55, 2034-2039. (8) Keana, J. F. W., and Cai, S. X. (1990) New reagents for photoaffinity labeling: Synthesis and photolysis of functionalized perfluorophenyl azides. J. Org. Chem. 55, 3640-3647. (9) Keana, J. F. W., and Cai, S. X. (1989) Functionalized perfluorophenyl azides: New reagents for photoaffinity labeling. J. Fluorine Chem. 43, 151-154. (10) Cai, S. X., and Keana, J,.F. W. (1989) 4-Azido-2-iodo-3,5,6trifluorophenylcarbonyl derivatives. A new class of functionalized and iodinated perfluorophenyl azide photolabels. Tetrahedron Lett. 30, 5409-5412.
3Ary~rlfluoro~~ylp~zlrlnes
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(1986)3-(Trifl~oromethy1)-3-(m-[~~I]-iodophenyl)- Registry No. la, 87736-85-4; lb, 135481-93-5; 4a, 135481diazirine photolabels a substrate-binding site of rat hepatic 94-6; Sa, 135481-95-7; 6a, 704-36-9;6b, 135481-96-8; 7a, 50562cytochrome P-450 form PB-4. Biochemistry 25, 4797-4803. 01-1; 9a, 106-38-7;9b, 51554-93-9; loa, 394-59-2; lob, 65440-56(24) Montecucco, C., Schiavo, G., Brunner, J., Duflot, E., Bo4; 1 la, 75703-25-2; 11b, 135481-97-9; 12a, 135481-98-0; 12b, 135481-99-1;13a, 87736-82-1; 13b, 135482-00-7; PhH, 71-43-2; quot, p., and Roa, M. (1986) Tetanus toxin is labeled with photoactivatable phospholipids at low pH. Biochemistry 25, MeOH, 67-56-1; CCA, 56-23-5; EtsSiH, 617-86-7; EtaNH, 109919-924. 89-7; Li, 7439-93-2; p-MeCaH,Li, 2417-95-0; FsCCOnEt, 383-63(25) Kreig, U. C., Isaacs, B. S., Yemul, S. S., Esmon, C. T., Bay1; MsC1, 124-63-0; cyclohexane, 110-82-7; hydroxylamine hyley, H., and Johnson, A. E. (1987) Interaction of blood drochloride, 5470-11-1.
