A GENERAL PROCESS FOR THE PREPARATION OF 6-SUBSTITUTED OR 5,6-DISUBSTITUTED DERIVATIVES OF 2-AMINO-ISONICOTINIC ACID

Abstract

This invention relates to a novel synthetic method for the preparation of 6-substituted or 5,6-disubstituted derivatives of 2-amino-isonicotinic acid.

Claims

1. A process for preparing 2-amino-isonicotinic acid derivatives of formula I ##STR00033## in which R1 is C.sub.1-C.sub.6-alkyl- or C.sub.6-C.sub.10-aryl-; R2 is H, C.sub.1-C.sub.6-alkyl- or C.sub.6-C.sub.10-aryl-; or R1 and R2 together form a C.sub.2-C.sub.5-alkyl- group such that a ring is formed; R3 is C.sub.1-C.sub.4-alkyl-; R4 is C.sub.1-C.sub.4-alkyl-; comprising the reaction of compound (1) ##STR00034## with a compound of formula II ##STR00035## in which R1, R2, R3 and R4 have the meaning as in formula I, in which water is eliminated.

2. The process according to claim 1, further comprising hydrolyzing the ester groups COOR3 and COOR4 of the 2-amino-isonicotinic acid derivatives of formula I to give intermediate compound of formula III ##STR00036## in which R1 and R2 have the meaning as in formula I.

3. The process according to claim 2, further comprising reacting the intermediate compound of formula III under conditions facilitating decarboxylation to give a compound of formula IV ##STR00037## in which R1 and R2 have the meaning as in formula I.

4. The process according to claim 1 in which R1 is methyl-, ethyl-, iso-propyl-, tert-butyl- or phenyl-; R2 is H or methyl-; or R1 and R2 together form a CH.sub.2CH.sub.2CH.sub.2 or CH.sub.2CH.sub.2CH.sub.2CH.sub.2 group such that a ring is formed; R3 is ethyl- or methyl-; R4 is ethyl- or methyl-.

5. The process according to claim 1 in which R1 is methyl-, ethyl-, iso-propyl-, tert-butyl- or phenyl- and R2 is H; or R1 is ethyl- and R2 is methyl-; or R1 and R2 together form a CH.sub.2CH.sub.2CH.sub.2 group such that a ring is formed; R3 is ethyl-; R4 is ethyl-.

6. The process according to claim 1, wherein the reaction comprises NaOEt in EtOH for elimination of water.

7. The process according to claim 2, wherein an inorganic base is used for hydrolysis of the ester groups.

8. The process according to claim 2, wherein NaOH, LiOH, KOH or Ba(OH).sub.2 is used for hydrolysis of the ester groups.

9. The process according to claim 2, wherein the reaction mixture is adjusted to a pH in the range of 5-6 with an acid after hydrolysis of the ester groups.

10. The process according to claim 2, wherein the reaction mixture is adjusted to a pH in the range of 5-6 with hydrochloric acid or H.sub.2SO.sub.4 after hydrolysis of the ester groups.

11. The process according to claim 3, wherein concentrated H.sub.2SO.sub.4 is used for decarboxylation.

12. The process according to claim 3, wherein decarboxylation is conducted in the presence of LiCl, NaCl or MgCl.sub.2.

13. The process according to claim 3, wherein decarboxylation is conducted at a temperature of 120 to 150 C.

Description

DESCRIPTION OF THE FIGURE

[0090] FIG. 1. X-ray structure of Compound 3

INSTRUMENTS

[0091] The single crystal was mounted in a capillary. Diffraction was performed on a Bruker SMART DUO CCD area detector diffractometer using graphite-monochromatic Mo-K radiation (=0.71073 A) operated at 1500 W power (50 kV, 30 mA).

[0092] .sup.1H (400 MHz) and .sup.13C (100 MHz) spectra were recorded with a Bruker Avance III UltraShield-Plus Digital NMR spectrometer at room temperature in D.sub.2O or DMSO-d.sub.6 as solvent. Chemical shifts are reported in ppm relative to TMS or signal of deuterated solvent.

Synthetic Examples and Experimental Data

Example 1: Preparation of 2-amino-6-methyl-pyridine-3,4-dicarboxylic acid (Compound 4)

[0093] ##STR00016##

[0094] To a solution of 136 mg NaOEt in 2 mL EtOH is added 330 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature. A total of 310 mg of ethyl 2,4-dioxopentanoate is added next. The reaction mixture is heated to reflux for 2 h. Then, 1.6 g of 20% NaOH aq. solution is added under reflux, the mixture is refluxed for another 1 h. It is cooled to room temperature, the reaction mixture is adjusted to pH=5-6. The product is precipitated as solid. It is collected by filtration and washed with 2 mL water twice. A total of 327 mg (yield 85.0%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.45 (s, 1H), 2.24 (s, 3H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 177.11, 173.73, 157.99, 156.92, 150.84, 111.45, 111.12, 22.66; MS (m/z+1): 197.1.

[0095] Diester 3 is obtained during the above described procedure although not isolated but directly converted into diacid 4. Alternatively, compound 3 is obtained and isolated via the following procedure:

##STR00017##

[0096] To a solution of 0.29 g of NaOEt in 4.0 mL of EtOH is added 0.7 g of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 0.66 g of 2,4-dioxo-pentanoic acid ethyl ester. The reaction mixture is heated to reflux for 2 h. Ethanol is removed by evaporator at 50 C., and then 10 mL of water and 10 mL of ethyl acetate are added and stirred for 10 min. The aqueous phase is then discarded and the organic phase is washed with 10 mL of water. A total of 0.95 g (yield 90.2%) of the desired product (Compound 3) is obtained after the organic phase being concentrated to dryness. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.49 (s, 1H), 6.38 (br, 2H), 4.33 (q, 2H, J=7.2 Hz), 4.29 (q, 2H, J=7.2 Hz), 2.40 (s, 3H), 1.37 (t, 3H, J=7.2 Hz), 1.33 (t, 3H, J=7.2 Hz); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 168.38, 166.26, 163.05, 158.08, 145.27, 111.23, 100.42, 61.74, 61.34, 24.54, 14.09, 13.99; MS (m/z+1): 253.37.

TABLE-US-00001 TABLE 1 Crystal data and structure refinement for cd213567 (Compound 3) Identification code cd213567 Empirical formula C.sub.12H.sub.16N.sub.2O.sub.4 Formula weight 252.27 Temperature 293(2) K Wavelength 0.71073 Crystal system, space group Monoclinic, P2(1)/c Unit cell dimensions a = 8.4904 (9) alpha = 90 deg. b = 10.7915 (10) beta = 91.236(2) deg. c = 14.6320 (15) gamma = 90 deg. Volume 1340.3 (2) .sup.3 Z, calculated density 4, 1.250 mg/m.sup.3 Absorption coefficient 0.095 mm.sup.1 F(000) 536 Crystal size 0.21 0.15 0.11 mm Theta range for data collection 2.35 to 26.00 deg Limiting indices 0 <= h <= 10, 11 <= K <= 13, 18 <= l <= 17 Reflections collected/unique 7961/2627 [R(int) = 0.0355] Completeness to theta = 26.00 100.0% Absorption correction Empirical Max. and min. transmission 1.00000 and 0.59772 Refinement method Full-matrix least-squares on F.sup.2 Data/restraints/parameters 2627/50/194 Goodness-of-fit on F{circumflex over ()}2 1.059 Final R indices [I > R1 = 0.0589, wR2 = 0.1738 2sigma(I)] R indices (all data) R1 = 0.0794, wR2 = 0.1926 Extinction coefficient 0.008(4) Largest diff. Peak and hole 0.234 and 0.185 e..sup.3

TABLE-US-00002 TABLE 2 Atomic coordinates and equivalent isotropic displacement parameters (.sup.2) for cd213567 (Compound 3). U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. x y z U (eq) N1 0.90561 (19) 0.56682 (15) 0.10675 (11) 0.0590 (5) N2 0.9389 (3) 0.6643 (2) 0.02969 (13) 0.0851 (7) O1 0.8120 (3) 0.89046 (19) 0.04855 (12) 0.1279 (9) O2 0.7365 (2) 0.98258 (14) 0.07604 (11) 0.0819 (6) O3 0.4995 (2) 0.8713 (2) 0.19328 (13) 0.1005 (7) O4 0.7028 (2) 0.92509 (18) 0.28122 (12) 0.1020 (7) C1 0.8796 (2) 0.66852 (19) 0.05502 (13) 0.0599 (5) C2 0.7987 (2) 0.77321 (18) 0.08814 (12) 0.0565 (5) C3 0.7413 (2) 0.76564 (18) 0.17680 (12) 0.0541 (5) C4 0.7716 (2) 0.66224 (18) 0.22928 (13) 0.0585 (5) C5 0.8548 (2) 0.56481 (18) 0.19211 (13) 0.0568 (5) C6 0.8883 (3) 0.4505 (2) 0.24673 (16) 0.0785 (7) C7 0.7828 (3) 0.8846 (2) 0.03107 (15) 0.0715 (6) C8 0.7145 (4) 1.0975 (2) 0.0244 (2) 0.1038 (10) C9 0.6481 (7) 1.1880 (3) 0.0857 (3) 0.171 (2) C10 0.6339 (3) 0.8605 (2) 0.21610 (14) 0.0678 (6) C11 0.6404 (11) 1.0437 (8) 0.3202 (6) 0.1134 (18) C12 0.5778 (11) 1.0088 (9) 0.4047 (5) 0.135 (2) C11 0.5747 (9) 1.0007 (7) 0.3256 (6) 0.1062 (17) C12 0.6772 (9) 1.0941 (7) 0.3767 (6) 0.121 (2)

TABLE-US-00003 TABLE 3 Bond lengths [] and angles [deg] for cd213567 (Compound 3). N1C5 1.330(2) N1C1 1.349(3) N2C1 1.349(3) N2H2A 0.95(3) N2H2B 0.91(3) O1C7 1.198(3) O2C7 1.310(3) O2C8 1.462(3) O3C10 1.188(3) O4C10 1.308(3) O4C11 1.503(8) O4C11 1.516(7) C1C2 1.413(3) C2C3 1.398(3) C2C7 1.469(3) C3C4 1.376(3) C3C10 1.494(3) C4C5 1.384(3) C4H4 0.93 C5C6 1.494(3) C6H6A 0.96 C6H6B 0.96 C6H6C 0.96 C8C9 1.449(4) C8H8A 0.97 C8H8B 0.97 C9H9A 0.96 C9H9B 0.96 C9H9C 0.96 C11C12 1.408(11) C11H11A 0.97 C11H11B 0.97 C12H12A 0.96 C12H12B 0.96 C12H12C 0.96 C11C12 1.518(9) C11H11C 0.97 C11H11D 0.97 C12H12D 0.96 C12H12E 0.96 C12H12F 0.96 C5N1C1 119.18(16) C1N2H2A 117.1(15) C1N2H2B 117.2(16) H2AN2H2B 124(2) C7O2C8 117.44(18) C10O4C11 125.1(4) C10O4C11 106.6(3) C11O4C11 28.0(4) N2C1N1 115.36(18) N2C1C2 122.42(19) N1C1C2 122.21(17) C3C2C1 116.96(18) C3C2C7 123.09(18) C1C2C7 119.92(18) C4C3C2 120.02(17) C4C3C10 116.71(17) C2C3C10 123.03(18) C3C4C5 119.19(18) C3C4H4 120.4 C5C4H4 120.4 N1C5C4 122.35(18) N1C5C6 116.98(18) C4C5C6 120.66(18) C5C6H6A 109.5 C5C6H6B 109.5 H6AC6H6B 109.5 C5C6H6C 109.5 H6AC6H6C 109.5 H6BC6H6C 109.5 O1C7O2 121.1(2) O1C7C2 125.3(2) O2C7C2 113.57(18) C9C8O2 107.4(2) C9C8H8A 110.2 O2C8H8A 110.2 C9C8H8B 110.2 O2C8H8B 110.2 H8AC8H8B 108.5 C8C9H9A 109.5 C8C9H9B 109.5 H9AC9H9B 109.5 C8C9H9C 109.5 H9AC9H9C 109.5 H9BC9H9C 109.5 O3C10O4 124.3(2) O3C10C3 123.4(2) O4C10C3 112.23(18) C12C11O4 104.4(7) C12C11H11A 110.9 O4C11H11A 110.9 C12C11 H11B 110.9 O4C11H11B 110.9 H11AC11H11B 108.9 O4C11C12 99.2(5) O4C11H11C 111.9 C12C11H11C 111.9 O4C11H11D 111.9 C12C11H11D 111.9 H11CC11H11D 109.6 C11C12H12D 109.5 C11C12H12E 109.5 H12DC12H12E 109.5 C11C12H12F 109.5 H12DC12H12F 109.5 H12EC12H12F 109.5

[0097] Symmetry Transformations Used to Generate Equivalent Atoms:

TABLE-US-00004 TABLE 4 Anisotropic displacement parameters (.sup.2) for cd213567 (Compound 3). The anisotropic displacement factor exponent takes the form: 2 pi{circumflex over ()}2 [h{circumflex over ()}2 a*{circumflex over ()}2 U11 + . . . + 2 h k a* b* U12 ] U11 U22 U33 U12 U13 U23 N1 0.0666 (10) 0.0616 (10) 0.0491 (9) 0.0066 (8) 0.0108 (7) 0.0051 (7) N2 0.1334 (19) 0.0725 (13) 0.0505 (11) 0.0221 (13) 0.0304 (11) 0.0020 (10) O1 0.236 (3) 0.0952 (13) 0.0538 (11) 0.0561 (15) 0.0306 (13) 0.0107 (9) O2 0.1212 (14) 0.0625 (9) 0.0626 (10) 0.0156 (9) 0.0178 (9) 0.0001 (7) O3 0.0676 (11) 0.1343 (16) 0.1000 (14) 0.0346 (10) 0.0083 (9) 0.0016 (12) O4 0.1105 (14) 0.1155 (14) 0.0795 (11) 0.0534 (11) 0.0094 (10) 0.0456 (10) C1 0.0702 (12) 0.0672 (12) 0.0426 (10) 0.0044 (10) 0.0088 (9) 0.0074 (9) C2 0.0643 (12) 0.0630 (12) 0.0422 (10) 0.0068 (9) 0.0030 (8) 0.0061 (8) C3 0.0501 (10) 0.0675 (12) 0.0447 (10) 0.0051 (8) 0.0012 (7) 0.0084 (9) C4 0.0605 (11) 0.0725 (12) 0.0430 (10) 0.0059 (9) 0.0107 (8) 0.0018 (9) C5 0.0567 (11) 0.0654 (12) 0.0485 (10) 0.0015 (9) 0.0069 (8) 0.0029 (9) C6 0.0932 (17) 0.0784 (14) 0.0648 (13) 0.0186 (12) 0.0195 (12) 0.0106 (11) C7 0.0934 (16) 0.0733 (14) 0.0481 (12) 0.0150 (12) 0.0060 (10) 0.0052 (10) C8 0.151 (3) 0.0728 (16) 0.088 (2) 0.0191 (16) 0.0219 (18) 0.0138 (14) C9 0.299 (6) 0.080 (2) 0.137 (3) 0.054 (3) 0.071 (4) 0.016 (2) C10 0.0708 (14) 0.0831 (14) 0.0499 (12) 0.0205 (11) 0.0106 (10) 0.0014 (10) C11 0.125 (4) 0.123 (4) 0.093 (3) 0.048 (3) 0.003 (3) 0.045 (3) C12 0.153 (5) 0.145 (5) 0.107 (4) 0.049 (4) 0.019 (4) 0.030 (4) C11 0.119 (4) 0.112 (3) 0.087 (3) 0.043 (3) 0.010 (3) 0.048 (3) C12 0.132 (4) 0.114 (4) 0.116 (4) 0.042 (3) 0.004 (4) 0.059 (4)

TABLE-US-00005 TABLE 5 Hydrogen coordinates and isotropic displacement parameters (.sup.2) for cd213567 (Compound 3). x y z U(eq) H4 0.7367 0.6578 0.289 0.070 H6A 0.9008 0.3814 0.2062 0.118 H6B 0.8024 0.4347 0.2867 0.118 H6C 0.9834 0.4619 0.2824 0.118 H8A 0.8147 1.1266 0.002 0.125 H8B 0.6438 1.0837 0.0276 0.125 H9A 0.5501 1.1576 0.1082 0.257 H9B 0.6302 1.2643 0.0534 0.257 H9C 0.7201 1.2022 0.1361 0.257 H11A 0.7241 1.104 0.3287 0.136 H11B 0.5592 1.0788 0.2803 0.136 H12A 0.4855 0.9589 0.3944 0.202 H12B 0.5502 1.0817 0.4385 0.202 H12C 0.655 0.9621 0.439 0.202 H11C 0.5126 0.9511 0.3667 0.127 H11D 0.5058 1.0402 0.2806 0.127 H12D 0.7422 1.0518 0.4211 0.181 H12E 0.6113 1.1529 0.407 0.181 H12F 0.7427 1.1367 0.3342 0.181 H2A 0.978 (3) 0.586 (2) 0.0501 (17) 0.079 (7) H2B 0.916 (3) 0.729 (3) 0.0680 (17) 0.084 (8)

TABLE-US-00006 TABLE 6 Torsion angels [deg] for cd213567 (Compound 3). C5N1C1N2 178.17(19) C5N1C1C2 0.5(3) N2C1C2C3 179.3(2) N1C1C2C3 2.1(3) N2C1C2C7 2.7(3) N1C1C2C7 175.92(19) C1C2C3C4 3.4(3) C7C2C3C4 174.57(19) C1C2C3C10 170.79(19) C7C2C3C10 11.3(3) C2C3C4C5 2.1(3) C10C3C4C5 172.39(18) C1N1C5C4 1.9(3) C1N1C5C6 179.32(19) C3C4C5N1 0.6(3) C3C4C5C6 179.31(19) C8O2C7O1 2.9(4) C8O2C7C2 178.9(2) C3C2C7O1 170.0(3) C1C2C7O1 12.1(4) C3C2C7O2 11.8(3) C1C2C7O2 166.12(19) C7O2C8C9 174.1(3) C11O4C10O3 17.2(6) C11O4C10O3 6.4(5) C11O4C10C3 166.1(5) C11O4C10C3 170.3(4) C4C3C10O3 102.2(3) C2C3C10O3 72.2(3) C4C3C10O4 74.6(3) C2C3C10O4 111.1(2) C10O4C11C12 103.4(8) C11O4C11C12 48.7(11) C10O4C11C12 164.0(6) C11O4C11C12 28.2(10)

[0098] Symmetry Transformations Used to Generate Equivalent Atoms:

TABLE-US-00007 TABLE 7 Hydrogen bonds for cd213567 (Compound 3) [ and deg.]. DH . . . A D(DH) D(H . . . A) D(D . . . A) <(DHA) N2H2B . . . O1 0.91(3) 1.98(3) 2.680(3) 133(2) N2H2A . . . N(1)#1 0.95(3) 2.11(3) 3.049(3) 170(2) #1x + 2, y + 1, z

[0099] Symmetry Transformations Used to Generate Equivalent Atoms:

Example 2: Preparation of 2-amino-6-methyl-isonicotinic acid (Compound 5)

[0100] ##STR00018##

[0101] To a slurry of 154 mg of 2-amino-6-methyl-pyridine-3,4-dicarboxylic acid in 0.65 mL of NMP are added 50 mg of LiCl H.sub.2O and 190 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 130 C. and stirred for 48 h. It is then cooled to 20-30 C., and 1.6 mL of water is added. The resulting reaction mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL water twice. A total of 100 mg (yield 83.7%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.69 (s, 1H), 6.61 (s, 1H), 2.13 (s, 3H); .sup.13C NMR: (100 MHz, D.sub.2O with NaOD) 177.78, 158.62, 156.05, 147.21, 112.60, 106.08, 22.66; MS (m/z+1): 153.1.

Example 3: Preparation of 2-amino-6-methyl-isonicotinic acid methyl ester (Compound 6)

[0102] ##STR00019##

[0103] To a slurry of 340 mg of 2-amino-6-methyl-isonicotinic acid in 1.6 mL of methanol is added 170 mg of conc. sulfuric acid slowly at room temperature. The reaction mixture is heated to reflux for 6 h and then cooled to room temperature. Methanol is removed by evaporator at 50 C. A total of 1.6 mL of water is added and the mixture is adjusted to pH=6.5-7.0. The product is precipitated as solid. It is collected by filtration and washed with 1 mL water twice. A total of 190 mg (yield 51.2%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, DMSO-d.sub.6): 6.78 (d, 2H), 6.24 (s, 2H), 3.84 (s, 3H), 2.31 (s, 3H); .sup.13C NMR (100 MHz, DMSO-d.sub.6): 165.06, 160.00, 157.32, 138.21, 109.33, 104.49, 52.20, 23.74; MS (m/z+1): 167.1.

Example 4: Preparation of 2-amino-6,N,N-trimethyl-isonicotinamide (Compound 7)

[0104] ##STR00020##

[0105] To a slurry of 110 mg of 2-amino-6-methyl-isonicotinic acid in 1.1 mL of dichloromethane is added 0.01 mL of DMF. The mixture is cooled to 0-5 C. and 122 mg of oxalyl chloride is added slowly. The reaction mixture is stirred at 0-5 C. for 1 h, and then 400 mg of 40% dimethylamine aq. solution is added dropwise. The mixture is stirred for 1 h, followed by addition of 50 mg of NaCl. The organic phase is separated. The aqueous phase is extracted by 0.4 mL dichloromethane twice. The combined organic phase is washed with 0.3 mL of 25% sodium chloride aq. solution. It is then concentrated by evaporator and 1 mL of toluene is added. The resulting solid is collected by filtration and washed with 1 mL of toluene. A total of 94 mg (yield 72.0%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, DMSO-d.sub.6): 6.28 (s, 1H), 6.14 (s, 1H), 6.06 (s, 2H), 2.93 (s, 3H), 2.86 (s, 3H), 2.24 (s, 3H); .sup.13C NMR (100 MHz, DMSO-d.sub.6): 168.97, 159.31, 156.45, 145.57, 107.95, 101.95, 34.18, 32.76; MS (m/z+1): 180.2.

Example 5: Preparation of 2-amino-6-ethyl-pyridine-3,4-dicarboxylic acid (Compound 10a)

[0106] ##STR00021##

[0107] To a solution of 136 mg of NaOEt in 2 mL of EtOH is added 330 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 340 mg of ethyl 2,4-dioxohexanoate. The reaction mixture is heated to reflux for 2 h. A total of 1.6 g of 20% NaOH aq. solution is added under reflux. The mixture was refluxed for another 1 h then cooled to room temperature. It is adjusted to pH=5-6. The product is precipitated as solid. It is collected by filtration and washed with 2 mL of water twice. A total of 350 mg (yield 84.3%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.45 (s, 1H), 2.47 (q, 2H), 2.08 (t, 3H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 177.17, 173.79, 163.34, 156.94, 150.92, 111.74, 109.81, 29.99, 13.16; MS (m/z+1): 211.1.

Example 6: Preparation of 2-amino-6-ethyl-isonicotinic acid (Compound 11a)

[0108] ##STR00022##

[0109] To a slurry of 165 mg of 2-amino-6-ethyl-pyridine-3,4-dicarboxylic acid in 0.65 mL of NMP are added 50 mg of LiClH.sub.2O and 190 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 130 C. for 48 h, then cooled to 20-30 C. A total of 1.6 mL of water is added. The reaction mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 110 mg (yield 84.3%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.79 (s, 1H), 6.14 (s, 1H), 2.47 (q, 2H), 1.05 (t, 3H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 173.99, 162.53, 158.84, 147.61, 111.26, 106.30, 30.00, 13.35; MS (m/z+1): 167.1.

Example 7: Preparation of 2-amino-6-isopropyl-pyridine-3,4-dicarboxylic acid (Compound 10b)

[0110] ##STR00023##

[0111] To a solution of 74 mg of NaOEt in 1 mL of EtOH, is added 180 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 200 mg of ethyl 5-methyl-2,4-dioxohexanoate. The reaction mixture is heated to reflux for 2 h. A total of 860 mg of 20% NaOH aq. solution is added under reflux. The reaction mixture is refluxed for another 1 h, and then cooled to room temperature. It is adjusted to pH=5-6. The crude product is obtained by removing solvent completely, which is used to the next step directly. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.63 (s, 1H), 2.88 (m, 1H), 1.25 (d, 6H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 177.25, 173.83, 167.35, 156.79, 150.86, 111.87, 108.04, 35.25, 21.52; MS (m/z+1): 225.1.

Example 8: Preparation of 2-amino-6-isopropyl-isonicotinic acid (Compound 11b)

[0112] ##STR00024##

[0113] To a slurry of the above 2-amino-6-isopropyl-pyridine-3,4-dicarboxylic acid in 1 mL of NMP are added 65 mg of LiClH.sub.2O and 265 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 130 C. for 48 h, and then cooled to 20-30 C. A total of 2.5 mL of water is added. The mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 135 mg (yield 69.7% in 2 steps) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 7.00 (s, 1H), 6.86 (s, 1H), 2.88 (m, 1H), 1.25 (d, 6H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 173.99, 166.71, 158.06, 147.77, 109.59, 106.56, 35.30, 21.75; MS (m/z+1): 181.0.

Example 9: Preparation of 2-amino-6-tert-butyl-pyridine-3,4-dicarboxylic acid (Compound 10c)

[0114] ##STR00025##

[0115] To a solution of 68 mg of NaOEt in 1 mL of EtOH is added 166 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 200 mg of ethyl 5,5-dimethyl-2,4-dioxohexanoate. The reaction mixture is heated to reflux for 2 h. A total of 790 mg of 20% NaOH aq. solution is added under reflux. The mixture is refluxed for another 1 h, and then cooled to room temperature. It is adjusted to pH=5-6. The crude product is obtained by removing solvent completely, which is used to the next step directly. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.57 (s, 1H), 1.10 (s, 9H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 177.24, 173.96, 169.12, 156.66, 150.26, 111.80, 107.42, 36.25, 29.06; MS (m/z+1): 239.0.

Example 10: Preparation of 2-amino-6-tert-butyl-isonicotinic acid (Compound 11c)

[0116] ##STR00026##

[0117] To a slurry of above 2-amino-6-tert-butyl-pyridine-3,4-dicarboxylic acid in 1 mL of NMP are added 65 mg of LiCl.H.sub.2O and 245 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 140 C. for 48 h, and then cooled to 20-30 C. A total of 2.5 mL of water is added. The mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 115 mg (yield 59.3% in 2 steps) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.93 (s, 1H), 6.62 (s, 1H), 1.10 (s, 9H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 174.13, 168.73, 158.95, 147.32, 108.85, 106.40, 36.35, 29.32; MS (m/z+1): 195.1.

Example 11: Preparation of 2-amino-6-phenyl-pyridine-3,4-dicarboxylic acid (Compound 10d)

[0118] ##STR00027##

[0119] To a solution of 136 mg of NaOEt in 2 mL of EtOH is added 330 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 440 mg of 2,4-dioxo-4-phenyl-butyric acid ethyl ester. The reaction mixture is heated to reflux for 2 h. A total of 1600 mg of 20% NaOH aq. solution is added under reflux. The mixture is refluxed for another 1 h, and then cooled to room temperature. It is adjusted to pH=5-6. The product is precipitated as solid. It is collected by filtration, and washed with 1 mL of water twice. A total of 405 mg (yield 78.5%) of the desired product is obtained after being dried in vacuum oven at 60 C. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.67 (q, 2H), 7.35 (q, 3H), 6.90 (s, 1H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 176.74, 173.71, 157.35, 156.43, 150.68, 138.23, 129.41, 128.03, 127.03, 113.11, 109.34; MS (m/z+1): 259.1.

Example 12: Preparation of 2-amino-6-phenyl-isonicotinic acid (Compound 11d)

[0120] ##STR00028##

[0121] To a slurry of 258 mg of 2-amino-6-phenyl-pyridine-3,4-dicarboxylic acid in 1 mL of NMP is added 60 mg of LiClH.sub.2O and 245 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 130 C. for 48 h and then cooled to 20-30 C. A total of 2.5 mL of water is added. The mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 180 mg (yield 84.1%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 7.49 (q, 2H), 7.23 (q, 3H), 7.13 (s, 1H), 6.75 (s, 1H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 173.53, 159.47, 156.17, 147.69, 138.69, 129.07, 128.77, 126.96, 111.13, 107.67; MS (m/z+1): 215.0.

Example 13: Preparation of 2-amino-6-ethyl-5-methyl-pyridine-3,4-dicarboxylic acid (Compound 14a)

[0122] ##STR00029##

[0123] To a solution of 74 mg of NaOEt in 1 mL of EtOH is added 180 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 200 mg of ethyl 3-methyl-2,4-dioxohexanoate. The reaction mixture is heated to reflux for 2 h. A total of 1.29 g of 20% NaOH aq. solution is added under reflux. The mixture is reflux for another 3 h, and then cooled to room temperature. It is adjusted to pH=5-6. The crude product is obtained by removing solvent completely, which was used to the next step directly. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 2.68 (q, 2H), 2.14 (s, 3H), 1.18 (t, 3H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 177.40, 173.61, 162.06, 155.43, 151.94, 115.49, 110.70, 28.06, 13.72, 12.67; MS (m/z+1): 225.1.

Example 14: Preparation of 2-amino-6-ethyl-5-methyl-isonicotinic acid (Compound 15a)

[0124] ##STR00030##

[0125] To a slurry of above 2-amino-6-ethyl-5-methyl-pyridine-3,4-dicarboxylic acid in 1 mL of NMP are added 65 mg of LiClH.sub.2O and 265 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 130 C. for 48 h, and then cooled to 20-30 C. A total of 2.5 mL of water is added. The mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 118 mg (yield 61.0% in 2 steps) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.21 (s, 1H), 2.43 (q, 2H), 1.95 (s, 3H), 0.94 (t, 3H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 177.17, 160.40, 156.04, 151.58, 115.57, 103.37, 27.71, 13.47, 12.69; MS (m/z+1): 181.1.

Example 15: Preparation of 2-amino-6,7-dihydro-5H-cyclopenta[b]pyridine-3,4-dicarboxylic acid (Compound 14b)

[0126] ##STR00031##

[0127] To a solution of 74 mg of NaOEt in 1 mL of EtOH is added 180 mg of 3-amino-3-imino-propanoic ethyl ester hydrochloride at room temperature, followed by addition of 200 mg of 2-oxo-cyclopentanecarboxylic acid ethyl ester. The reaction mixture is heated to reflux for 2 h. A total of 860 mg of 20% NaOH aq. solution is added under reflux. The mixture is refluxed for another 1 h, and then cooled to room temperature. It is adjusted to pH=5-6. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 200 mg (yield 82.9%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 2.68 (t, 2H), 2.61 (t, 2H), 1.95 (m, 2H); .sup.13C NMR (100 MHz, D.sub.2O with NaOD): 176.77, 173.75, 165.36, 157.06, 147.52, 122.96, 110.19, 33.51, 28.31, 22.42; MS (m/z+1): 223.1.

Example 16: Preparation of 2-amino-6,7-dihydro-5H-cyclopenta[b]pyridine-4-carboxylic acid (Compound 15b)

[0128] ##STR00032##

[0129] To a slurry of 200 mg of 2-amino-6,7-dihydro-5H-cyclopenta[b]pyridine-3,4-dicarboxylic acid in 0.8 mL of NMP are added 54 mg of LiCl.H.sub.2O and 216 mg of conc. H.sub.2SO.sub.4. The reaction mixture is heated to 130 C. for 48 h, and then cooled to 20-30 C. A total of 2 mL of water is added. The mixture is adjusted to pH=6-7. The product is precipitated as solid. It is collected by filtration and washed with 1 mL of water twice. A total of 120 mg (yield 74.8%) of the desired product is obtained after being dried at 60 C. in vacuum oven. .sup.1H NMR (400 MHz, D.sub.2O with NaOD): 6.37 (s, 1H), 2.64 (t, 2H), 2.50 (t, 2H), 1.76 (m, 2H); .sup.13CNMR (100 MHz, D.sub.2O with NaOD): 175.13, 164.23, 157.65, 144.80, 125.10, 104.95, 33.08, 29.26, 22.25; MS (m/z+1): 179.0.