HETEROCYCLES

Paper | Regular issue | Vol. 85, No. 5, 2012, pp. 1089-1103
Received, 19th January, 2012, Accepted, 12th March, 2012, Published online, 22nd March, 2012.
DOI: 10.3987/COM-12-12432

■ Syntheses of 5-Amino-2-phenyl-4(3H)-pyrimidinone Derivatives Starting with Glycine

Daisuke Takahashi,* Yutaka Honda, and Kunisuke Izawa*

Research Institute for Bioscience products and Finechemicals, Ajinomoto Co., Inc., 1780 Hinaga, Yokkaichi, Mie, 510-0885, Japan

Abstract

N-Cbz derivative of 5-amino-2-phenyl-4(3H)-pyrimidinone was prepared from sodium salt of methyl hydroxymethylene glycinate and benzamidine hydrochloride in good yield. However, the reaction with N-substituted benzamidine did not proceed to give the desired pyrimidinone. In contrast, the reaction of 4-ethoxymethylene-2-phenyl-5(4H)-oxazolone readily prepared from hippuric acid and N-substituted benzamidine proceeded nicely to give 5-(benzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid in high yield.

INTRODUCTION
5-Amino-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid (1a) has attracted attention as a core molecule for the development of novel nonpeptidic enzyme inhibitors. In particular, several drug candidates such as human leukocyte elastase (also known as human neutrophil elastase) inhibitors for the treatment of COPD (chronic obstructive pulmonary disease)1 and anti-inflammatory effects,2 chymase inhibitors for the treatment of heart failure,3 and serine protease inhibitors for anti-malaria action4 have been designed and are being developed through the use of 1a as peptide mimetics for the P2-P3 scaffold of the enzyme, since derivatives of 1a are known to show high bioavailability.

The first synthesis of 1b was reported by Veale et al.5 using the reaction of methoxymethylenemalonate (2) with N-(2,2-dimethoxyethyl)benzamidine (3) followed by Curtius rearrangement and subsequent oxidation of aldehyde with NaClO2 to the corresponding acid 1b (eq.1). So far, this method has been widely used to synthesize many pharmaceutical candidates. However, there is a risk of explosion associated with this process on an industrial scale. To avoid dangerous azide chemistry, Nakai et al. transformed the carboxyl group to an amino group by Lossen rearrangement using hydroxamate.6 Alternatively, Kojima et al. reported an efficient method for the synthesis of 1a consisting of the catalytic reduction of 5-nitropyrimidinone (8) prepared from 3-methoxy-2-nitroacrylate (6) and benzamidine derivatives 7a (eq.2).7

Recently, new strategies for the synthesis of 1a were presented in a patent application by Sugiura et al.8 First, they used the reaction of N-protected dimethyl aminomalonate with N-carboxymethyl benzamidine (7b) to prepare 5-(benzyloxycarbonylamino)-4-hydroxy-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid (10), which was subjected to chlorination followed by reduction to obtain 1a (eq. 3).

The patent also reported that the reaction of 4-ethoxymethylene-2-phenyl-5(4H)-oxazolone with N-carboxymethyl benzamidine gave the desired pyrimidinone derivative 1c in good yield. Since, we have independently developed a method that is very similar to theirs and some of our data are completely novel, in this report we describe our studies on the synthesis of 1a and 1b aiming at the production of these compounds on an industrial scale.

RESULTS AND DISCUSSION
Synthetic approach to 1a via N-(benzyloxycarbonyl)-2-(hydromethylene)glycinate.
We began our study by using 2-(hydroxymethylene)glycinate as a starting material instead of methoxymethylenemalonate (2) or 3-methoxy-2-nitroacrylate (6), which require the transformation of carboxylate or nitro groups into an amino substituent via Curtius rearrangement using azide or the reduction of a nitro group in a later step. We considered that our proposed process would be safer by avoiding these risky reagents and hazardous reactions.
Nemeryuk et al. reported the synthesis of N-formyl ethyl 2-(hydroxymethylene)glycinate 12 by the reaction of ethyl glycinate (11) with ethyl formate in the presence of sodium methoxide. Compound 12 was then converted to 5-formamido-4(3H)-pyrimidinones (14a and 14b) by the reactions of methyl amidines 13a (R=Me) and S-ethyl thioisourea 13b (R=Set) in rather poor and excellent yields, respectively (eq. 4).9

We intended to synthesize 5-(tert-butoxycarbonylamino)-2-phenyl-4(3H)-pyrimidinone 17 in a similar manner from N-Boc-glycine methyl ester 15, which has a more useful protecting group. The reaction of 15 with ethyl formate in the presence of potassium tert-butoxide gave (hydroxymethylene)glycinate 16 as a potassium salt, though it was very difficult to isolate as pure crystals in high yield due to high solubility in aqueous solution. Thus, we reacted 16 formed in situ with benzamidine hydrochloride (13c) to obtain 17 as crystals in 34% isolated yield (eq. 5). We also attempted the synthesis of N-Cbz derivative in the same manner, but failed, probably due to cleavage of the N-Cbz group under strong basic conditions. As a result, we abandoned this approach toward the synthesis of 1.

To improve the yield in (hydroxymethylene)glycinate formation, we investigated the use of two-step reaction sequences as follows. According to the method reported by Toplak et al.,10 N-Cbz-2-(dimethylaminomethylene)glycinate (19) was synthesized from N-Cbz-glycine methyl ester (18) with tert-butoxy-bis(dimethylamino)methane (Brederick’s reagent) in almost quantitative yield. Compound 19 has been reported to react with primary alkylamine to give β-alkylamino derivatives in acetic acid.11 Thus, we examined the reaction of 19 with benzamidine hydrochloride (13c) and N-tert-butoxycarbonylmethyl benzamidine 7a. Unexpectedly, we found that the desired reactions did not proceed at all in either case. Interestingly, however, sodium salt 21 of methyl (hydroxymethylene)-glycinate, which is readily prepared from 19 by treatment with diluted hydrochloric acid followed by sodium methoxide, reacted nicely with 13c to give 5-(benzyloxycarbonylamino)- 2-phenyl-4(3H)-pyrimidinone (22) in very good yield (eq. 6).

In contrast, the reaction of 21 with N-substituted benzamidine 7a under similar reaction conditions did not proceed to give the desired pyrimidinone 23 (eq. 7).

We speculate that the substitution of benzamidine lowered the reactivity of amidine toward the sodium salt 21. It has been reported that the alkylation of 22 with ethyl bromoacetate occurs with no selectively to afford the desired ester as a minor product along with the N1- and O-alkylated isomers.5 We also obtained a very similar result in the reaction of N-Boc pyrimidinone 17 with tert-butyl bromoacetate.12
To achieve efficient pyrimidinone formation, we further investigated the electronic effect of a β-substituent on the reactivity of the olefin bond by changing hydroxymethylene group to methoxymethylene compound 24, which is readily achieved in 85% yield by the treatment of 21 with dimethyl sulfate.

Methyl ester 24 was allowed to react with the free form of benzamidine 7a at 80 °C in toluene to give the desired compound 23 in 31% yield (eq. 8), while the acetoxy compound obtained by acetylation of 21 gave only a trace amount of 23.
As noted above, the synthetic approach using methyl N-Cbz (hydroxymethylene)glycinate (21) efficiently gave N3 non-substituted pyrimidinone 22, but was not applicable to the industrial-scale synthesis of 23 due to the low yield of cyclization.


Synthesis of 1a via 4-hydroxymethylene-5-oxazolone.
To improve the yield of cyclization of hydroxymethylene glycinate with amidine derivatives, it was considered that the activation of olefin might be essential. We anticipated that 4-alkoxymethylene- 5-oxazolone (25) may be one of the most suitable intermediates for this purpose.

Mukerjee et al. reported that the oxazolone 25 reacted with S-benzyl isothiouronium hydrochloride salt (26) to give 5-benzoylamino-2-benzylsulfanyl-4(3H)-pyrimidinone (27) in 74% yield (eq. 9).13 Encouraged by this report, we examined the reaction of 25 with benzamidine derivative, with particular focus on N-substituted benzamidine 7a. Since there have been several reports on the addition-elimination reactions of 25 to replace a β-ethoxy group with a β-amino group,14 we expected that the risk of a ring-opening reaction by amine attack was low. The oxazolone 25 that was easily prepared from hippuric acid by the Erlenmeyer method was heated with benzamidine derivative 7a in toluene after treatment with base to make a free form. To our delight, the desired pyrimidinone 28a was obtained in 97% yield (eq. 10).　The use of N-(carboxymethyl)benzamidine 7b instead of 7a gave a lower yield (58%) of the product 1c, while it does not require deprotection of the ester group. 15

The cyclization reactions using other oxazolones prepared from ring-substituted hippuric acids gave similar results in each case: p-Cl 28b; 96%, p-Me 28c; 95%, p-OMe 28d; 82%, and o-Cl 28e; 76%. The reaction could also be applied to the syntheses of 2-(p-fluorophenyl) derivative (29; 89%) using the corresponding amidine.

The resulting t-butyl ester 28a was treated with trifluoroacetic acid at ambient temperature to achieve the selective and complete deprotection of t-butyl ester followed by recrystallization from ethyl acetate to give pure product 1c in 85% yield (eq. 11). When we carried out the deprotection reaction by treatment with NaOMe/MeOH followed by aqueous NaOH solution, we obtained 1a in only 70% yield along with impurity after conventional acid workup. However, simultaneous cleavage of the N-benzoyl and t-butyl groups was achieved by refluxing methanol solution of 28a in the presence of NaOH (3 equiv.) to give 1a in 90% yield after acid workup.

The pyrimidinone 1a was treated with benzyl chloroformate under basic conditions using a two-phase reaction to give N-Cbz pyrimidinone 1b in 77% yield. Formylation of 1a was also efficiently performed by a conventional method to give 1d in 97% yield.

The precise mechanism for the cyclization reaction of ethoxymethylene oxazolone 25 with benzamidinoacetate 7a is not yet clear. If the nucleophilic attack of an amidine derivative to the carbonyl carbon at the 5-position occurred, N1-alkylated pyrimidinone 33 should be formed via the intermediate 32. However, only a trace amount of the product 33 was observed in the reaction mixture. Therefore, the initial attack of the amidine 7a should occur at the β-position of the exo-olefin bond. This phenomenon is consistent with the result that the ethoxy group of the oxazolone could be changed to an amino group (Scheme 1).

Meanwhile, 2-methyl-4-alkoxymethylene-5-oxazolone (35) could also be prepared by the treatment of N-acetylglycine (34) with triethyl orthoformate and acetic anhydride. However, the oxazolone 35 is an oily compound and difficult to obtain in a satisfactory yield. Thus, we attempted to carry out the reaction without the isolation of 35, and obtained the N-acetyl pyrimidinone derivative 36 in 19% overall yield (eq. 13).

Notably, the N-acetyl group of 36 can be deacetylated under remarkably mild conditions. Therefore, the N-acetyl group should be a very good protecting group if a facile and efficient method for the synthesis of 35 can be developed in the future.16

CONCLUSION
Versatile methods for the synthesis of 5-(benzyloxycarbonylamino)-2-phenyl-4(3H)-pyrimidinone 22 and its N3-carboxymethyl derivative 1b were developed using glycine as a starting material. The processes do not require hazardous reaction conditions or reagents such as azide and nitro compounds. It should be straightforward to scale-up these processes to an industrial scale.

EXPERIMENTAL
All reagents were purchased and used without further purification. Thin-layer chromatography (TLC) was conducted on precoated TLC plates (Merck 60F250). High-performance liquid chromatography (HPLC) was performed with a Hitachi L-6000 pump and an L-4000 UV detector system using an Inertsil ODS-2 column. Melting points were measured with a Büchi B-545 or a Yanaco melting point apparatus MP model and are uncorrected. NMR spectra were obtained on a Varian XL-300 spectrometer. All proton NMR spectra were measured in CDCl3 or DMSO-d6 solvent, and chemical shifts are reported as δ values in parts per million relative to tetramethylsilane (δ 0.00) or CHCl3 (δ 7.26) as an internal standard. Data are reported as follows: chemical shift (integrated intensity or assignment, multiplicity, coupling constants in hertz, assignment). All carbon NMR spectra were measured in CDCl3 or DMSO-d6 solvent, and chemical shifts are reported as δ values in parts per million relative CDCl3 (δ 77.0) or DMSO-d6 (δ 39.5) as an internal standard. Infrared (IR) spectra were recorded on a SHIMADZU IR Prestige-21 Fourier transform infrared spectrophotometer equipped with a Smith Dura Sample IR II ATR unit and are reported in wave number (cm-1). Mass spectra (MS) were obtained with a ThermoQuest TSQ700 or a JEOL JMS-HX110 instrument with ESI (electrospray) or FAB (fast atom bombardment) ionization. High-resolution mass spectra (HRMS) were obtained with a JEOL MS700V (JEOL Datum Ltd.).

5-(tert-Butoxycarbonylamino)-2-phenyl-4(3H)-pyrimidinone (17).
To a THF suspension (10 mL) of potassium t-butoxide (0.59 g, 5.3 mmol) were added dropwise a THF solution (10 mL) of N-Boc-glycine methyl ester (1.00 g, 5.3 mmol) and methyl formate (0.35 g, 6.5 mmol) on an ice bath. After the mixture was stirred for 3 h at the same temperature, benzamidine hydrochloride 13c (0.82 g, 5.2 mmol) was added. The reaction mixture was stirred at 40 °C for an additional 14 h and concentrated under reduced pressure. The residue was washed with water. The resulting precipitate was triturated with ether, collected and dried to give compound 17 as a white solid (0.52 g, 34%).
Mp 227.5-227.8 °C, IR (neat): 1720, 1647, 1519, 1477, 1153, 711, 617, 565 cm-1, 1H-NMR (CDCl3) δ 1.62 (9H, s), 7.25 (1H, s), 7.52 (3H, m), 8.02 (2H, d, J = 3.0 Hz), 8.82 (1H, s), 11.74 (1H, s), 13C-NMR (CDCl3) δ 28.3, 125.8, 126.7 129.1, 131.4, 132.1, 137.2, 148.5, 152.2, 158.7, HRMS: Calcd for C15H17N3O3 [M+M]+: 288.1348, Found: 288.1335.

Methyl N-benzyloxycarbonyl-2-(hydroxymethylene)glycinate sodium salt (21).
Methyl N-Cbz-2-(dimethylaminomethylene)glycinate (19)10 (2.38 g, 8.55 mmol) was dissolved in MTBE (20 mL). Into the solution was poured aqueous 1M HCl (15 mL) on an ice bath. After the mixture was stirred for 2 h at rt, the organic layer was separated, washed with brine and added dropwise to a 28% NaOMe/MeOH solution (1.50 g, 8.00 mmol). The mixture was concentrated under reduced pressure. The resulting precipitate was triturated with Et2O, collected and dried to give compound 21 as a white solid (2.12 g, 91%).
Mp 105.8-106.4 °C. IR (neat) 1668, 1556, 1520, 1438, 1278, 1186, 1124, 1055, 734, 694 cm-1. 1H-NMR(DMSO-d6) δ 3.40 (3H, s), 4.96 (2H, s), 6.83 (1H, s), 7.32-7.37 (5H, m), 8.75 (1H, s), 13C-NMR (DMSO-d6) δ 48.7, 65.0, 97.2, 126.5, 127.6, 128.3, 137.5, 155.6, 168.7, 172.0., HRMS: Calcd for C12H13NO5Na [M+M]+: 274.0691, Found: 274.0667.

5-(Benzyloxycarbonylamino)-2-phenyl-4(3H)-pyrimidinone (22).
To a solution of sodium salt 21 (1.54 g, 5.62 mmol) in MeCN (19 mL) was added benzamidine hydrochloride 13c (0.88g) and the mixture was stirred at 70 °C for 14 h. The reaction mixture was concentrated under reduced pressure. To the residue was added water (15 mL) and the mixture was stirred for 1 h. The resulting precipitate was triturated with Et2O, collected and dried to give compound 22 as a white solid (1.54 g, 86%).
Mp 217.1-218.9 °C, IR (neat); 3315, 1651, 1533, 1502, 1230, 1217, 1049, 949, 765, 687, 600, 569 cm-1. 1H-NMR (DMSO-d6) δ 5.18 (2H, s), 7.32-7.57 (8H, m), 8.06-8.09 (2H, m), 8.46 (1H, s), 8.79 (1H, s), 13.0 (1H, brs). 13C-NMR (DMSO-d6) δ 66.1, 124.8, 127.3, 127.6, 127.9, 128.3, 128.6, 131.1, 132.1, 136.3, 150.9, 153.4, 158.8, 158.9. HRMS: Calcd for C18H15N3O3 [M+M]+: 322.1191, Found: 322.1163.

Methyl N-Cbz-methoxymethylene glycinate (24).
Sodium salt of 21 (300 mg, 1.10 mmol) was suspended in MeCN (5 mL) and dimethyl sulfate (0.105 mL, 1.04 mmol) was added dropwise. The mixture was stirred at 40 °C for 17 h. The resulting precipitate was filtered off and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel chromatography (hexane-EtOAc) to give 24 as colorless oil (248 mg, 85%).
IR (neat): 3325, 2951, 1701, 1653, 1496, 1249, 1226, 1122, 1053,736, 696 cm-1. 1H-NMR (CDCl3) δ 3.76 (3H, s), 3.93 (3H, s), 5.10 (1H, s), 5.20 (2H, s), 5.78 (1H, s), 7.28-7.33 (5H, m). 13C-NMR (CDCl3) δ 51.8, 62.1, 67.3, 107.6, 128.2, 128.5, 128.6, 136.2, 155.2, 165.7. HRMS m/z Calcd for C13H15NO5 [M+M]+: 266.1028, Found: 266.1031.

5-(Benzyloxycarbonylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (23).
To a suspension of 7a (675 mg, 2.5 mmol) in toluene (10 mL) was added 10% aqueous solution (8 mL) of sodium carbonate with vigorous stirring. After separation of the organic layer, the aqueous layer was extracted with toluene (5 mL). The combined organic layer was washed with brine and dried over Na2SO4. To the organic layer was added 24 (500 mg, 1.9 mmol). The mixture was stirred at 80 °C for 17 h and washed with 1M HCl and brine. After concentration, the residue was purified by silica gel column chromatography (hexane-EtOAc, 10:1 to 2:1) to give 23 as a white solid (246 mg, 31%).
Mp 108.7-108.9 °C; IR (neat) 3265, 1734, 1656, 1514, 1489, 1365, 1213, 1151, 1091, 771, 696 cm-1. 1H-NMR (DMSO-d6) δ 1.43 (9H, s), 4.53 (2H, s), 5.17 (2H, s), 7.26-7.54 (10H, m), 8.77 (1H, s). 13C-NMR (DMSO-d6) δ 27.9, 48.8, 67.5, 83.1, 125.1, 128.1, 128.2, 128.4, 128.6, 128.9, 130.3, 134.1, 134.8, 135.7, 152.7, 153.0, 157.7, 166.1. HRMS: Calcd for C24H25N3O5 [M+M]+: 436.1872, Found: 436.1875.

5-(Benzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (28a).
To a suspension of 7a (5.00 g, 18.5 mmol) in toluene (70 mL) were added sodium carbonate (8.0 g) and water (70 mL) with vigorous stirring. After phase separation, the aqueous layer was extracted with toluene (70 mL). The combined organic layer was washed with brine and dried over Na2SO4. The organic layer was added dropwise to a solution of 2-phenyl-4-ethoxymethylene 5-(4H)-oxazolone17 (25) (3.09 g, 14.2 mmol) in MeCN (5 mL). The mixture was stirred at 80 °C for 17 h and washed with 1M HCl, saturated aqueous NaHCO3 solution and brine. After concentration, the residue was added dropwise to hexane and stirred. The resulting crystals were collected by filtration and dried under reduce pressure to give the desired pyrimidinone 28a as pale yellow crystals (5.59 g, 97%).
Mp 188.5-190.1 °C. IR (neat): 1734, 1649, 1512, 1485, 1365, 1238, 1149, 771, 698, 597 cm-1. 1H-NMR (DMSO-d6) δ 1.31 (9H, s), 4.57 (2H, s), 7.51-7.65 (8H, m), 797-8.00 (2H, m), 8.79 (1H, s), 9.58 (1H, s). 13C-NMR (CDCl3) δ 27.9, 49.0, 83.3, 125.2, 125.3, 127.3, 128.2, 128.9, 128.9, 129.0, 130.5, 132.3, 133.7, 153.4, 158.4, 165.6, 166.2. MS(ESI) m/z; [M+M]+: 406.2. Anal. Calcd for C23H23N3O4: C, 68.13; H, 5.72; N, 10.36. Found: C, 68.20; H, 5.65; N, 10.30.

5-(p-Chlorobenzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (28b).
Yield: 96%; Mp 165.6-168.1 °C. 1H-NMR (CDCl3) δ 1.46 (9H, s), 4.58 (2H, s), 7.42-7.55 (6H, m), 7.86-7.89 (2H, m), 8.76 (1H, s), 9.24(1H, s). 13C-NMR (CDCl3) δ 28.3, 49.4, 83.7, 125.5, 128.5, 129.1, 129.3, 129.5, 130.9, 132.4, 134.4, 137.2, 139.1, 154.0, 158.6, 164.8, 166.5. Anal. Calcd for C23H22ClN3O4: C, 62.80; H, 5.04; N, 9.55. Found：C, 62.85; H, 5.01; N, 9.48.

5-(p-Methylbenzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (28c).
Yield 95%; Mp 161.6-163.9 °C. 1H NMR (CDCl3) δ 1.46 (9H, s), 2.43 (3H, s), 4.58 (2H, s), 7.24-7.31 (2H, dd, J = 6.5, 1.7 Hz), 7.45-7.54 (6H, m), 7.82-7.85 (2H, dd, J = 6.5, 1.7 Hz), 8.79 (1H, s), 9.27 (1H, s). 13C-NMR (CDCl3) δ 21.9, 28.3, 49.4, 83.6, 125.7, 127.7, 128.5, 129.3, 129.9, 130.8, 131.2, 134.5, 136.9, 143.4, 153.6, 158.7, 165.9, 166.6. Anal. Calcd for C24H25N3O4: C, 68.72; H, 6.01; N, 10.02. Found C, 68.92; H, 5.99; N, 9.92.

5-(p-Methoxybenzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (28d).
Yield 82%; Mp 160.9-163.6 °C, 1H-NMR (CDCl3) δ 1.46 (9H, s), 3.84 (3H, s), 4.58 (2H, s), 6.96-7.00 (2H, d, J = 9.8 Hz), 7.45-7.54 (6H, m), 7.89-7.92 (2H, d, J = 9.8 Hz), 8.74 (1H, s), 9.26 (1H, s). 13C-NMR (CDCl3) δ 28.3, 49.4, 55.9, 83.6, 114.4, 125.8, 126.3, 128.6, 129.3, 129.6, 130.8, 134.5, 136.8, 153.5, 158.7, 163.3, 165.5, 166.6. Anal. Calcd for C24H25N3O5: C, 66.19; H, 5.79; N, 9.65. Found C, 66.23; H, 5.73; N, 9.57.

5-(o-Chlorobenzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (28e).
Yield 76%; 1H-NMR (CDCl3) δ 1.48 (9H, s), 4.57 (2H, s), 7.32-7.55 (8H, m), 7.89-7.92 (1H, d, J = 6.0 Hz), 8.89 (1H, s), 9.27(1H, s). 13C-NMR (CDCl3) δ 27.9, 48.9, 83.2, 125.2, 127.2, 128.2, 128.9, 130.4, 130.5, 130.6, 131.1, 132.1, 134.1, 134.2, 137.2, 153.8, 158.1, 164.7, 166.1. HRMS: Calcd for C23H22ClN3O4 [M+M]+ 440.1377, Found: 440.1368.

5-(p-Fluorobenzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (29).
Yield 89%; 1H-NMR (CDCl3) δ 1.46 (9H, s), 4.56 (2H, s), 7.16 (2H, dd, J = 8.5 Hz), 7.45-7.56 (4H, m), 7.91 (2H, d, J = 7.3 Hz), 8.81 (1H, s), 9.22 (1H, s). 13C-NMR (CDCl3) δ 28.0, 49.0, 83.4, 116.0, 116.3, 125.4, 127.3, 128.9, 130.2, 130.3, 130.4, 132.4, 133.7, 136.5, 152.4, 158.3, 162.2, 165.6, 166.2. HRMS: Calcd for C23H22FN3O4 [M+M]+: 424.1672, found: 424.1692.

5-(Benzoylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid (1c).
To a suspension of N-carboxymethyl benzamidine (7b)8 (300 mg, 1.68 mmol) in iPrOH (5 mL) were added 21% NaOEt (631 mg) and 4-ethoxymethylene-2-phenyl-5-oxazolone (25) (364 mg, 1.68 mmol), and the mixture was stirred at 80 °C overnight. The solution was concentrated and washed by the addition of water (6 mL) and MTBE (6 mL), and the aqueous layer was adjusted to pH 8 with aqueous NaOH. The aqueous layer was acidified with hydrochloric acid. The precipitate was filtered and dried to give 1c as pale yellow crystals (324mg, 58%).
Mp 247.0-248.7 °C (lit.,8 244.0-245.3 °C). IR (neat) 1728, 1656, 1516, 1487, 1227, 1199, 773, 704, 592 cm-1. 1H-NMR (DMSO-d6) δ 4.56 (2H, s), 7.53-7.65 (8H, m), 7.97 (2H, d, J = 5.1 Hz), 8.81 (1H, s), 9.55 (1H, s). 13C-NMR (DMSO-d6) δ 48.6, 124.8, 128.0, 128.4, 129.0, 130.7, 132.5, 133.8, 134.4, 140.2, 155.3, 158.1, 165.8, 169.1. Anal. Calcd for C, 65.32; H, 4.33; N, 12.03. Found: C, 65.12; H, 4.18; N, 11.88.

5-Amino-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid (1a).
To a solution of 28a (1.00 g 2.5 mmol) in MeOH (8 mL) was added NaOH (0.40 g, 10 mmol), and the mixture was stirred under reflux for 17 h. To the reaction mixture was added water (5 mL), and the solution was concentrated under reduced pressure. The residue was poured into MTBE (3 mL) and acidified to pH 3.0 with 6M hydrochloric acid. The resulting precipitates were washed with water/MTBE and dried under reduced pressure to give 1a as white crystals (585 mg, 96%).
Mp. 202.4-204.7 °C. IR (neat); 2580, 1691, 1616, 1516, 1427, 1382, 1298, 1182, 773, 715, 686, 547 cm-1. 1H-NMR (DMSO-d6) δ 4.46 (2H, s), 5.22 (2H, brs), 7.34 (1H, s), 7.41-7.49 (5H, m). HRMS: Calcd for C12H11N3O3 [M+M]+: 246.0878, Found: 246.0882.

5-(Benzyloxycarbonylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid (1b).
Sodium salt of compound 1a (0.56 g, 2.1 mmol) was dissolved in water (6 mL), and benzyl chloroformate (0.43 mL, 2.5 mmol) was added dropwise for 1 h while the pH was maintained at 6-8 by the addition of saturated aqueous NaHCO3 solution. After the mixture was stirred for 2 h, it was washed with toluene. The aqueous layer was acidified to pH 1 with 6M hydrochloric acid and extracted twice with EtOAc. The combined organic layers were washed with brine and concentrated. After the addition of hexane, the resulting precipitate was collected by filtration and dried under reduced pressure to give 1b (0.61 g, 77%).
Mp 183.6-185.9 °C. IR (neat); 3298, 1734, 1658, 1516, 1491, 1213, 1182, 1086, 986, 767, 748, 694 cm-1. 1H-NMR (DMSO-d6) δ 4.52 (2H, s), 5.20 (2H, s), 7.34-7.55 (10H, m), 8.47 (1H, s), 9.01 (1H, s), 13.3 (1H, br). 13C-NMR(DMSO-d6) δ 48.0, 66.3, 124.7, 127.7, 128.0, 128.4, 128.6, 130.1, 134.1, 136.4, 137.4, 153.4, 153.8, 157.2, 168.7, 169.7. HRMS: Calcd for C20H17N3O5 [M+M]+: 380.1246, Found: 380.1262.

5-(Formylamino)-6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid (1d).
Formic acid (1.5 mL) was added dropwise to acetic anhydride (0.5 mL) at room temperature for 1 h, and 1a (0.1 g, 0.41 mmol) was then added to the mixture, which was stirred for 2 h. Toluene was added and the mixture was concentrated under reduced pressure. The residue was washed with EtOAc and the resulting crystals were collected by filtration and dried under reduced pressure to give 1d (0.11 g, 97%).
Mp 218-220 °C. IR (neat): 3282, 1643, 1604, 1512, 1487, 1232, 1186, 1141, 777, 723, 700, 696 cm-1. 1H-NMR (DMSO-d6) δ 4.53 (2H, s), 7.49-7.58 (5H, m), 8.14 (1H, s), 8.39 (1H, s), 8.89 (1H, s), 10.05 (1H, s). 13C-NMR (DMSO-d6) δ 48.5, 124.8, 128.4, 129.0, 130.6, 134.4, 137.2, 154.3, 157.2, 161.2, 163.4, 169.0. HRMS: Calcd for C13H11N3O4 [M+M]+: 274.0828, Found: 274.0809.

5-(Acetylamino)–6-oxo-2-phenyl-1(6H)-pyrimidineacetic acid tert-butyl ester (36).
To a suspension of N-acetylglycine 34 (0.2 g, 1.7 mmol) in EtOAc (1.5 mL) were added triethyl orthoformate (0.76 g, 5.1 mmol) and acetic anhydride (1.74 g, 16.4 mmol). After the reaction mixture was stirred at 95 oC for 14 h, it was cooled to room temperature, and washed with saturated aqueous NaHCO3 solution and brine. After evaporation with toluene, the residue was added to a solution of the free form of benzamidine 7a (2.22 mmol) and stirred at 80 °C for 15 h. The mixture was washed with 1M hydrochloric acid, saturated aqueous NaHCO3 solution, and brine, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/EtOAc) to give pyrimidineacetic acid tert-butyl ester 36 (0.11 g, 19%) as a pale yellow solid.
Mp 150-152 °C. IR (neat): 3329, 1735, 1645, 1508, 1354, 1226, 1147, 771, 667, 590 cm-1. 1H-NMR (CDCl3) δ 1.45 (9H, s), 2.23 (3H, s), 4.54 (2H, s), 7.48 (5H, m), 8.03 (1H, s), 9.09 (1H, s). 13C-NMR (DMSO-d6) δ 24.4, 27.9, 49.0, 94.1, 125.1, 128.1, 128.9 130.0, 134.0, 136.6, 153.3, 158.0, 166.1, 168.8. HRMS: Calcd for C18H21N3O4 [M+M]+: 344.1610, Found: 344.1584.

ACKNOWLEDGEMENT
We would like to thanks Mrs. Naoko Hirose for taking analytical data.

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