摘要:

J. CHEM. SOC. PERKIN TRANS. 2 1995 Carbon-skeleton Rearrangement of an Amino Acid Derivative as Mediated by Hydrophobicvitamin B,,Covalently Bound toa Lipid Species ina Bilayer Membrane Yukito Murakami," Yoshio Hisaeda, Akihiro Ogawa and Teruhisa Ohno Department of Chemical Science and Technology, Faculty of Engineering, Kyushu University, Fukuoka 812, Japan Diethyl 2-acetylamino-2-methylpropanedioate co-ordinated to a hydrophobic vitamin B,, covalently bound to a peptide lipid underwent a carbon-skeleton rearrangement to afford diethyl 2-acetylaminobutanedioate in the single-walled vesicle of N,N-bis( hexadecyl) -N"-(6-sulfohexanoyl) -L-ala n i n am ide under photoIysis cond it ions. We have been interested in the catalytic activity of vitamin B,, placed in hydrophobic microenvironments so as to simulate catalytic functions of the holoenzymes concerned.In this context, we have prepared an artificial holoenzyme composed of a synthetic bilayer membrane and a hydrophobic vitamin B12. The artificial holoenzyme was found to catalyse isomerization reactions characteristic of the natural holoenzymes, as effected Z-by both motional repression and desolvation effects provided by synthetic bilayer membranes.' In order to enhance the catalytic efficiency in the isomerization reactions, we have pre- pared novel hydrophobic vitamin B, ,derivatives covalently bound to a lipid species2 and performed model reactions in simulation of catalysis by methylmalonyl-CoA mutase and c=oa-methyleneglutarate mutase, as mediated by the novel vitamin IB,, lipid in a bilayer membrane formed with (SO,-)-C5Ala2Ci,.3 For the purpose of exploring the catalytic efficiency of the vitamin B,, lipid (1) in an isomerization reaction of a non-natural substrate, the reaction of diethyl 2- acetylamino-2-methylpropanedioatebound to the hydrophobic vitamin B, ,was investigated in the (SO, -)C5Ala2C, 6 vesicle 1 x=Y=none*z=c104 under photolysis conditions as described below. 2 X = CH2C(NHCOMe)(C02Et)2, Y = H20, Z = C104Diethyl 2-acetylamino-2-bromomethylpropanedioate, a brominated non-natural substrate, was prepared after a method reported previously as shown by reaction (1).This brominated ,CO2Prsubstrate was identified by 'H NMR and IR measurements as well as by elemental analysis.Alkylated complex 2 was prepared by the reaction of 1 with diethyl 2-acetylamino-2- C02Pr bromomethylpropanedioateand sodium tetrahydroborate in a manner as reported previously' [reaction (2)] to give a dark Z-brown solid.? Complex 4 was derived from 3 by following a similar method to give a dark brown solid.$ The alkylated complexes (2 and 4) showed electronic spectra characteristic of tervalent cobalt complexes with a Co-C bond and were converted into the corresponding tervalent cobalt complexes without an alkyl ligand upon cleavage of the Co-C bond by aerobic photolysis (Fig. 1). 3 X=Y=none.Z=CD4Peptide lipid (SO3-)C,Ala2C1 6 was prepared previously. Diethyl 2-acetylamino-2-methylpropanedioate(A) and diethyl 4 X = CH&(NHCOMe)(CaEt)2, Y = H20, Z = C04 2-acetylaminobutanedioate (B) were prepared as authentic Mesamples for the corresponding reaction products after procedures reported previously and confirmed to be suffi- (%-)[CH&CNHCH I FN,,[CHdlgMe Na+ II [CH2]1@00 f Yield 63%; ;Lmax(CHzC12)/nm 266 (E 1.6 x lo3 dm3 mol-' cm-I), 305 (1.9 x lo3), 317 (1.9 x lo3), 421 (7.3 x lo2) and 466 (8.5 x lo2) (Found: C, 61.6; H, 8.6; N, 4.8.Cl18H197ClCoN8Na0z9S requires: C, 60.53; H, 8.48;N, 4.79%). $ Yield 74%; Imax(CH,Cl,)/nm 264 (E 1.8 x lo3 dm3 mol-' cm-'), 293 ciently pure by 'HNMR measurements as well as by GLC and (1.6 x lo3), 313 (1.5 x lo3), 416 (7.0 x 10,) and 454 (6.6 x lo2) elemental analyses [refer to reaction (3)]. (Found: C, 57.9; H, 7.4; N, 4.5.C76H1 ,,CICoN,O,, requires: C, 57.73; In homogeneous solutions in methanol or benzene, the H, 7.59; N, 4.43%). reaction of the alkylated hydrophobic vitamin B,, (4) was 190 CO2Et COzEt I HCHO I HC -NHCOMe HOHzC-C -NHCOMe I I CO2Et CO2EtIPk3 CO2Et I BrH2C-C -NHCOMe I COzEt NaBH4 1 Or3 702Et H,F-Y-NHCOMe Br COZEt 7 v02Et 2or4 Table 1 Product analyses for photolysis of hydrophobic vitamin B,, derivatives in various media at 20.0 OCa Yield' (%) Medium * Complex A B C CH,OH 4 55-57 0-2 19-25 C6H6 4 2-6 0-3 78-82 (S0,-)C5Ala2C,, vesicle 4 29-33 22-29 22-26 (SO, -)C5Ala2C,6 vesicle 2 25-26 29-36 10-12 A solution containing a complex (1.0 x lo4 mol dm-,) was irradiated with a 500 W tungsten lamp at a distance of 30 cm under argon atmosphere for 1 h.(SO,-)C,Ala2C1, (5.0 x mol drn-,) in aqueous phosphate buffer (20 cm3; 1.0 x lo-, mol drn-,; p 0.01 with KCl; pH 7.0). 'Products were analysed by GLC. Total yields are less than 100% due to losses during extraction and evaporation treatments. carried out under anaerobic irradiation with visible light in a manner as described previously.' On the basis of GLC analysis, an unexpected product was obtained in addition to the simple reduction product (A) and the rearranged one (B) [refer to reaction (3)]. The unexpected product was found to be a major component of the whole products in benzene, ca. 80%. Therefore, the reaction mixture was concentrated and hexane was added to the concentrate to precipitate the hydrophobic vitamin BIZ.The filtrate was evaporated to dryness and the residue was dissolved in a small amount of dichloromethane. The resulting solution was applied on a preparative GLC column packed with Silicon SE-30 to give a white powder.§ The unknown product was confirmed to be diethyl 2-acetylaminopropanedioate (C)[refer to reaction (3)] by referring to NMR and GLC data obtained for the authentic sample obtained from Tokyo Kasei Co., Tokyo, Japan as a guaranteed reagent. The reactions of alkylated complexes 2 and 4 were carried out in the single-compartment vesicle as follows. An aqueous phosphate buffer (20 cm3; 1.0 x mol dm-3; p 0.01 with KCl; pH 7.0) containing (S03-)C5Aki2C16 (1.0 x lo4 mol) 9SH(500 MHz; CDCI,, Me&) 1.30 (6 H, t), 2.08 (3 H, s), 4.24-4.31 (4 H, m), 5.16 (1 H, d) and 6.52 (1 H, d). J.CHEM. SOC. PERKIN TRANS. 2 1995 I-....... 300 400 500 600 A Inm Fig. 1 Electronic spectra of hydrophobic vitamin B,, derivatives before photolysis (solid lines) and after irradiation with a 500 W tungsten lamp at a distance of 40 cm for 1 min (dotted lines) in dichloromethane at 20.0 ? 0.1 "C: (a), 2 (3.7 x lo4); (b), 4 (4.8 x lo-' mol dm-,) 70pEt H2C-y-NHCOMeI C02Et 1-CO2Et COzEt COZEt I I 1 H3C-y-NHCOMe + H2C-CH-NHCOMe + HC-NHCOMe (3)I I COZEt CO2Et C02 Et A B C was sonicated for 15 min with a probe-type sonicator at 30 W to give a clear solution. After the solution was deoxygenated with argon gas, ca.0.2 cm3 of a methanol solution containing the alkylated complex (2 or 4) (2.0 x lop6mol) was added to it. The alkylated complex was allowed to undergo photolysis with visible light under argon atmosphere at 20.0 k 0.1 "C. After the alkylated complex was completely photolysed as confirmed by electronic spectroscopy, the resulting mixture was lyophilized. The residue was dissolved in dichloromethane and the filtrate was analysed by GLC (Table 1). J. CHEM. SOC. PERKIN TRANS. 2 1995 The product analyses for the reaction in various media are summarized in Table 1. The simple reduction product (A) was largely obtained in methanol because the solvent acts as an efficient hydrogen donor, while the methyl-eliminated product (C)was a major one in benzene due to lack of the hydrogen- donating ability of the medium.As a reference experiment in benzene, the 2-acetylamino-2,2-bis(ethoxycarbonyl)ethylradi-cal was produced by the reaction of the corresponding bromide with the Bu,Sn' radical derived from Bu,SnH and benzoyl peroxide under photolysis conditions. Under such conditions without the hydrophobic vitamin B, ,, only the reduction product (A) was generated. This result indicates that the methyl- eliminated product (C)is not obtained without participation of the hydrophobic vitamin B,,. On the other hand, relatively large amounts of the rearrangement product (B)were obtained in the (SO, -)C,Ala2C16 vesicle which provides a hydrophobic microenvironment for 2 and 4 in aqueous media, as compared with the reactions in methanol and benzene.In particular, the substrate species co-ordinated to the vitamin B,, lipid (1) underwent photolysis to afford the rearrangement product as the largest component in the whole products. As we have clarified previ~usly,~ the hydrophobic vitamin BI , derivative covalently bound to the lipid species is subjected to marked motional repression in the bilayer membrane, as compared with the simple hydrophobic vitamin B,, without lipid linkage, to enhance the rearrangement reaction. In conclusion, the motional repression and desolvation effects operated on the substrate-bound hydrophobic vitamin B,, tend to enhance the rearrangement of the substrate radical formed by photolysis.This fact also suggests that participation of the hydrophobic vitamin B,, in the transition state is crucial for the rearrangement reaction. Such microenvironmental effects provided by the bilayer membrane becomes more pronounced when the hydrophobic vitamin B,, is covalently bound to the lipid species. It must also be noted that the ethoxycarbonyl group seems to migrate much more readily than the acetyl- amino group under the present experimental conditions. References 1 Y. Murakami, Y. Hisaeda and T. Ohno, J. Chem. SOC.,Perkin Trans. 2, 1991,405. 2 Y. Murakami, Y. Hisaeda, A. Ogawa, T. Miyajima, 0.Hayashida and T. Ohno, Tetrahedron Lett., 1993,34,863. 3 Y. Murakami, Y. Hisaeda, A. Ogawa and T. Ohno, Chem. Lett., 1994, 1657; T. Ohno, A. Ogawa, Y. Hisaeda and Y. Murakami, J. Chem. SOC., Perkin Trans. 2,1994,2271; T. Ohno, A. Ogawa, Y. Hisaeda and Y. Murakami, Tetrahedron Lett., 1994,35,9589. 4 R. L. Buchman, F. H. Dean and F. L. M. Pattion, Can.J. Chem., 1962, 40,1571. 5 Y. Murakami, J. Kikuchi, T. Takaki, K. Uchimura and A. Nakano, J. Am. Chem. SOC.,1985,107,2161. 6 N. F. Albertson and S. Archer, J. Am. Chem. SOC.,1945,67,308. Paper 4/069741 Received 15th November 1994 Accepted 30th November 1994

ISSN:1472-779X    

DOI:10.1039/P29950000189

出版商:RSC    

年代:1995

数据来源: RSC