HETEROCYCLES

Paper | Special issue | Vol. 77, No. 2, 2009, pp. 953-970
Received, 28th July, 2008, Accepted, 18th September, 2008, Published online, 22nd September, 2008.
DOI: 10.3987/COM-08-S(F)70

■ Pterdines CXX. Synthesis and Properties of Tetrahydropterins Coupled to 1,4-Dihydropyridines

Joachim Rehse and Wolfgang Pfleiderer*

Department of Chemistry, University of Konstanz, Posttach 55 60, 78434 Konstantz, Germany

Abstract

N²-Isobutyroyl-5,6,7,8-tetrahydropterins (6-10) have been coupled with nicotinic acid to form the N⁵-nicotinoyl derivatives 11-15. Quaternization at the pyridine moiety led to 19-31 which can be reduced to the corresponding N-substituted 1,4-dihydropyridine dertivatives 35-39. Partial deacylation of the isobutyroyl group afforded the various types of terahydropterins 16-18, 32-34 and 40-42. The newly synthesized 5,6,7,8-tetrahydropterin derivatives have been characterized by pK_a-determinations, UV- and NMR-spectra as well as elemental analyses.

INTRODUCTION
Tetrahydrobiopterin (BH4) is an important cofactor for some aromatic monooxygenases which participate in the synthesis of tyrosine, L-Dopa and 5-hydroxytryptophan. A lack of this cofactor causes several neurological diseases such as Parkinson disease and atypical phenylketonuria. Since the potential clinical agent, tetrahydrobiopterin, does not penetrate the blood-brain-barrier very effectively2 this problem may be overcome by addition of a lipophilic substituent3-5 or by the attachment of a carrier moiety.6,7 The Bodor-system8-10 offers with the dihydropyridine [image.pict] pyridinium salt carrier an interesting alternative and we decided to investigate this possibility in the tetrahydropterin series.
The basic concept of this approach is illustrated by the coupling of nicotinic acid to a biologically active molecule, quaternization with alkylating agents at the pyridine moiety and followed by reduction of the pyridinium salt to the corresponding 1,4-dihydropyridine compound. Such a compound will be distributed on dispension in the body including the brain. The dihydropyridine moiety will be oxidized to form the quaternary salt which due to its ionic character should be eliminated fast from the body while the blood-brain-barrier should prevent its elimination from the brain. After cleavage of the nicotinoyl residue the biologically active compound is regenerated in the brain in free form. A properly selected carrier should either be eliminated or should be pharmacologically harmless. The overall result is a brain specific sustained release of the active molecule.

RESULTS AND DISCUSSION
We applied the Bodor concept first to three synthetic analogs of BH4, the 6-methyl-, the 6,7-dimethyl-, the 6-hydroxymethyl- and the 6,7-diphenyl-5,6,7,8-tetrahydropterin,11-13 respectively, all of which showing some cofactor activity in vitro.

The starting N2-isobutyroylpterins (1-5) have first been reduced catalytically with Pt under H2-atmosphere in a shaken apparatus to their corresponding 5,6,7,8-tetrahydro derivatives (6-10) which were then subject to acylation with nicotinoyl chloride in pyridine at rt to form selectively the N5-nicotinoyl derivatives (11-15). These substances were isolated as racemic mixtures due to the new chiral centers in 6- and 7 position, respectively. 5,6,7,8-Tetrahydropterins possess in N5-position their most nucleophilic center in form of a secundary amine type whereas the HN8 -side is part of a vinylogous amide moiety and is therefore less reactive under the chosen reaction conditions. The high hydrolytic stability of the N5-acyl bond is seen from the fact that treatment of 12-15 with sodium methoxide in MeOH at rt cleaves selectively only the N2-isopropionyl group to give 16-18. Reactions of 12-15 with various alkylating agents such as methyl, ethyl, n-propyl, n-pentyl and n-octyl iodide in MeOH or DMF as well as with benzyl bromide in DMSO solution led under mild conditions at rt for 1- 5 days in high yields to the N-alkylated pyridinium salts (19-31). Quarternization of the pyridine moiety takes place also selectively with 17 and 18 to yield 32-34. Reduction of several pyridinium salts under mild basic conditions with sodium dithionite to the corresponding 1,4-dihydronicotinoyl derivatives (35-39) worked only in a few cases (22-24, 28 and 29), especially in the N-benzyl series. Selective removal of the isobutyroyl group by ammonia treatment at rt resulted in the carrier molecules 40-42. The characterization of the newly synthesized pterin derivatives was achieved by elemental analyses, 1H-NMR spectra (experimental part) and the determination of the pKa values by the spectrophotometric method14 combined with UV-spectra (Tables 1, 2 and 3). On the basis of the pKa-values the defined UV-spectra of the monocation, neutral form and monoanion as well as the dication, monocation and zwitter iononic form have been determined to compare the equivalent molecular species as further proof of the structural assignments.

EXPERIMENTAL
General. TLC: precoated cellulose thin-layer sheets F 1440b LS 254 and silica gel thin-layer sheets F 1500 LS 254 from Schleicher and Schüll. Column chromatography: silica gel 60 from Merck. M.p.: Büchi Melting Point B-545; no corrections. The pKa measurements were performed by the spectrophotometric method.14 UV: Lambda 15 recording spectrometer from Perkin-Elmer: λmax (nm); log ε; (sh) shoulder. 1H-NMR: Bruker WM-250 spectrometer in δ (ppm) relative to TMS. Mass spectra: Firma Finnigan, model MAT 312. Elemental analyses were performed in the microanalytical laboratory of Konstanz University.

N2-Isobutyroylpterin (1): A suspenion of pterin (1.0 g, 6.1 mmol) in abs. pyridine (40 mL) was treated with isobutyric anhydride (10 mL) under reflux for 4 h. It was evaporated and the residue recrystallized from MeOH (180 mL) with charcoal to give 1.06 g (75%) colorless crystals, mp >290 °C (decomp.). pKa: 7.39. UV (pH 5): 214 (sh 4.13), 230 (4.16), 276 (4.14), 326 (3.87), 334 (sh 3.85); (pH 10): 224 (3.95), 252 (4.42), 282 (3.63), 339 (3.83). 1H-NMR (DMSO-d6): 1.15 (d, 6H, Me2C), 2.72 (sept, 1H, H-CMe2), 8.71 (d, 1H, H-C(6)), 8.92 (d, 1H, H-C(7)), 11.90 (s, 1H, H-N(3)), 12.32 (s, 1H, H-N). Anal. Calcd for C10H11N5O2 (233.2): C, 51.50; H, 4.75; N, 30.03. Found: C, 51.60; H, 4.82; N, 30.01.

N2-Isobutyroyl-6-methylpterin (2): To a suspension of 6-methylpterin15,16 (2.0 g, 0.011 mmol) in abs. pyridine (20 mL) was treated with isobutyric anhydride (5 mL) under reflux for 4.5 h. Charcoal was added to the hot solution, filtered and after cooling evaporated to dryness. The residue was treated with MeOH and the solid collected to give after drying in the oven at 100 °C 1.59 g (57%). Recrystallization from MeOH/H2O gave 1.02 g (37%) colorless needles, mp 285 °C. pKa: 7.64. UV (pH 5): 228 (4.12), 278 (4.20), 335 (3.88); (pH 10): 224 (sh 3.97), 253 (4.42), 282 (sh 3.73), 344 (3.84). 1H-NMR, (DMSO-d6): 1.12 (d, 6H, C(Me2), 2.59 (s, 3H, H3C-C(6)), 2.76 (sept, 1H, H-CMe2), 8.79 (s, 1H, H-C(7)), 11.89 (s, H-N(3)), 12.3 (bs, 1H, H-N). Anal. Calcd for C11H13N5O2 (247,3): C, 53.43; H, 5.30; N, 28.32. Found: C, 53.23; H, 5.31; N, 27.88.

N2-Isobutyroyl-6-isobutyroyloxymethylpterin (4): A suspension of 6-hydroxymethylpterin17 (4,0 g, 20.4 mmol) in abs. pyridine was treated with isobutyric anhydride (30 mL) under reflux for 5 h. After cooling MeOH (20 mL) was added, stirred for 30 min, then evaporated, and coevaporated with toluene. The residue was treated with EtOAc, the resulting precipitate collected, then dissolved in CHCl3 and purified by silica-gel column chromatography with CHCl3/MeOH 30:1. The main fraction was separated, evaporated and the residue recrystallized from n-hexane/CHCl3 to give 4.32 g (62 %) colorless crystals. mp 183 °C. pKa: 7.24. UV (pH 5): 222 (sh 4.12), 233 (4.15), 281 (4.33), 335 (3.92); (pH 10): 224 (sh 3.98), 256 (4.47), 284 (sh 3.74), 346 (3.89). 1H-NMR (DMSO-d6): 1.10-1.20 (2d, 12H, 2 Me2C), 2.52 (sept, 1H, H-CMe2), 2.72 (sept, 1H, H-CMe2), 5.33 (s, 2H, CH2), 8.91 (s, 1H, H-C(7)), 11.80 (s, 1H, H-N(3)), 12.22 (s, 1H, H-N). Anal. Calcd for C15H19N5O4 (333.4): C, 54.05; H, 5.75; N, 21.01. Found: C, 53.67; H, 5.75; N, 20.90.

N2-Isobutyroyl-6.7-diphenylpterin (5): A suspension of 6.7-diphenylpterin18 (5.3 g, 16.8 mmol) in abs. pyridine (60 mL) was treated with isobutyric anhydride (15 mL) under reflux for 2.5 h. After cooling down to 80 °C EtOH was added to the clear yellowish solution. On cooling a colorless precipitate separated, was collected, washed with MeOH and dried at 100 °C to give 6.0 g (92%), mp 269 °C. pKa: 7.63. UV (pH 5): 225 (4.44), 256 (4.26), 296 (4.30), 365 (4.19); (pH 10): 221 (sh 4.37), 252 (sh 4.37), 258 (4.38), 371 (4.15). 1H-NMR, (DMSO-d6): 1.13 (d, 6H, C(Me2), 2.80 (m, 1H, H-CMe2), 7.26-7.53 (m, 10H, 2 ph), 9.82 (s, H-N(3)), 12.5 (bs, 1H, H-N). Anal. Calcd for C22H19N5O2 (385.4): C, 68.56; H, 4.97; N, 18.17. Found: C, 67.94; H, 5.05; N, 17.97.

N2-Isobutyroyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (11): In a shaking apparatus a suspension of N2-isobutyroylpterin (1) (1.0 g, 4.3 mmol) in MeOH (100 mL) was reduced under H2-atmosphere in presence of PtO2 (100 mg) as catalyst. After 24 h 2 equivalents of H2 were consumed. The suspension was evaporated in vacuum to dryness and the residue treated with abs. pyridine (30 mL) and nicotinoyl chloride hydrochloride (1.03 g, 5.8 mmol) with stirring overnight. EtOH (20 mL) was added, stirred for 1 h and then the precipitate filtered off. Recrystallization from EtOH/H2O (1:1) with charcoal gave 0.385 g (26%) of a yellowish crystal powder, mp 297-299 °C (decomp.). pK: 3.16, 9.44. 1H-NMR, (DMSO-d6): 1.01 (d, 6H, C(Me2), 2.69 (sept, 1H, H-CMe2), 3.31 (m, 2H, H-C(7)), 3.48 (m, 2H, H-C(6)), 7.47 (s, 1H, H-N(8)), 7.38 (dd, 1H, nic-5), 7.79 (d, 1H, nic-4), 8.49 (d, 1H, nic-6), 8.59 (s, 1H, nic-2), 11.06 (s, H-N(3)), 11.38 (bs, 1H, H-N). Anal. Calcd for C16H18N6O3 x 0.25 H2O (346.9): C, 55.40; H, 5.38; N, 24.23. Found: C, 55.37; H, 5.54; N, 23.83.

N2-Isobutyroyl-6-methyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (12): Analogous to the preceding procedure with 2 (1.0 g, 4.05 mmol). The crude naterial was purified by recrystallization from MeOH (20 mL) with little charcoal to give 0.65 g (45%) colorless needles, mp 310 °C. pKa: 3.19, 9.68. 1H-NMR, (DMSO-d6): 1.03 (d, 6H, C(Me2), 1.08 (d, 3H, Me-C(6)), 2.69 (sept, 1H, H-CMe2), 3.29-3.49 (m, 2H, H-C(7)), 4.81 (m, 1H, H-C(6)), 7.43 (s, 1H, H-N(8)), 7.31 (dd, 1H, nic-5), 7.79 (d, 1H, nic-4), 8.49 (d, 1H, nic-6), 8.58 (s, 1H, nic-2), 11.06 (s, H-N(3)), 11.32 (bs, 1H, H-N). Anal. Calcd for C17H20N6O3 (356.4): C, 57.29; H, 5.66; N, 23.58. Found: C, 57.10; H, 5.77; N, 23.45.

N2-Isobutyroyl-6,7-dimethyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (13): A solution of N2-isobutyroyl-6,7-dimethyl-5,6,7,8-tetrahydropterin (8)5 (10.78 g, 33.7 mmol) in abs. pyridine (200 mL) was cooled to 0°C and under N2-atmosphere nicotinoyl chloride hydrochloride (8,5 g, 47 mmol) added with stirring. After stirring for 2 days under rt MeOH (10 ml) was added and the reaction mixture kept overnight in the icebox. The precipitate was collected, washed with acetone and ether and dried in the vacuum desiccator to give 7.3 g (58%) colorless powder, mp > 300 °C, From the filtrate were isolated another 1.46 g (12%). pKa: 3.16, 9.59. 1H-NMR, (DMSO-d6): 0.85 (d, 3H, Me-C(7)), 1.03 (d, 6H, C(Me2), 1.17 (d, 3H, Me-C(6)), 2.72 (sept, 1H, H-CMe2), 3.80 (m, 1H, H-C(7)), 4.59 (m, 1H, H-C(6)), 7.33 (bs, 1H, H-N(8)), 7.34 (dd, 1H, nic-5), 7.79 (d, 1H, nic-4), 8.48 (d, 1H, nic-6), 8.57 (s, 1H, nic-2), 11.08 (s, H-N(3)), 11.18 (bs, 1H, H-N). Anal. Calcd for C18H22N6O3 (370.4): C, 57.29; H, 5.66; N, 23.58. Found: C, 57.10; H, 5.77; N, 23.45.

N2-Isobutyroyl-6-isobutyroyloxymethyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (14): Analogous to procedure 11 with 4 (2.0, g, 6 mmol) in MeOH (180 mL) and PtO2 (0.36 g). The catalyst was filtered off and the filtrate evaporated to dryness. The residue was dissolved in abs. pyridine (80 mL) and nicotinoyl chloride hydrochloride (1.75 g, 7.75 mmol) added with stirring overnight. EtOH (10 mL) was added, stirred for 30 min, evaporated and twice coevaporated with toluene/EtOH. The residue was recrystallized from EtOH (30 mL) to give 1.18 g (44%) of colorless crystals, mp 300 °C (decomp.). pKa: 3.00, 9.47. 1H-NMR, (DMSO-d6): 0.99 (d, 6H, CMe2)), 1.04 (d, 6H, C(Me2), 2.49 (sept, 1H, H-CMe2), 2.71 (sept, 1H, H-CMe2), 3.35-3.51 (m, 2H, H-C(7)), 3.97 (m, 2H, O-CH2), 4.98 (bs, 1H, H-C(6)), 7.47 (bs, 1H, H-N(8)), 7.37 (dd, 1H, nic-5), 7.81 (d, 1H, nic-4), 8.51 (d, 1H, nic-6), 8.61 (s, 1H, nic-2), 11.02 (s, H-N(3)), 11.32 (bs, 1H, H-N). Anal. Calcd for C21H26N6O5 (442.5): C, 57.00; H, 5.42; N, 18.99. Found: C, 56.58; H, 5.89; N, 18.94.

N2-Isobutyroyl-6,7-diphenyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (15): Analogous to the preceding procedure with 5 (5.48 g, 14.2 mmol) in MeOH (350 mL) and PtO2 (0.5 g). The resulting suspension was evaporated, the residue dissolved in abs. pyridine (200 mL) and nicotinoyl chloride hydrochloride (3.4 g, 19.2 mmol) added. After stirring for 18 h the catalyst was filtered off and the filtrate evaporated to half of its volume. EtOH (50 mL) was added, the precipitate collected and recrystallized from little EtOH/DMF (1:1) to give 2.1 g (29%) of yellowish crystal powder, mp 289 °C. pKa: 3.06, 9.34. 1H-NMR, (DMSO-d6): 1.05 (d, 6H, C(Me2), 2.76 (sept, 1H, H-CMe2), 5.40 (m, 2H, H-C(7)), 5.65 (bs, 1H, H-C(6)), 6.80-7.20 (m, 10H, ph), 7.35 (dd, 1H, nic-5), 7.91 (d, 1H, nic-4), 8.17 (bs, 1H, H-N(8)), 8.53 (d, 1H, nic-6), 8.70 (s, 1H, nic-2), 11.02 (s, H-N(3)), 11.32 (bs, 1H, H-N). Anal. Calcd for C28H26N6O3 x 0.5 H2O (503.6): C, 66.78; H, 5.40; N, 16.68. Found: C, 66.64; H, 5.47; N, 16.56.
6-Methyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (16): In abs. MeOH (180 mL) was dissolved Na (0.234 g, 10 mmol) and then under stirring 12 (3.0 g, 8.4 mmol) added. After stirring for 12 h the yellowish solution was evaporated, the residue dissolved in H2O (80 mL), filtered, extracted with ether (30 mL) and then neutralized with AcOH to pH 7. After cooling overnight the precipitate was collected and dried in a vacuum desiccator to give 1.8 g (70%) colorless needles, mp 265-270 °C. pKa: 3.48, 10.46. 1H-NMR, (DMSO-d6): 0.98 (d, 3H, Me-C(6)), 3.22 (m, 1H, H-C(7)), 3.45 (m, 1H, H-C(7)), 4.80 (m, 1H, H-C(6)), 6.08 (bs, 2H, NH2), 7.02 (s, 1H, H-N(8)), 7.30 (dd, 1H, nic-5), 7.81 (d, 1H, nic-4), 8.40 (d, 1H, nic-6), 8.54 (s, 1H, nic-2), 9.71 (s, H-N(3)). Anal. Calcd for C13H14N6O2 x H2O (304.3): C, 51.31; H, 5.30; N, 27.62. Found: C, 51.75; H, 4.90; N, 27.74.

6,7-Dimethyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (17): A solution of 6,7-dimethyl-5,6,7,8-tetrahydropterin dihydrochloride5 (11.3 g, 42 mmol) in abs. pyridine (600 mL) was cooled to 5 °C and then under stirring and N2-atmosphere nicotinoyl chloride hydrochloride (9.5 g, 53.4 mmol) added. It was stirred at rt over night, evaporated and coevaporated with toluene/EtOH. The residue was treated with EtOH (100 mL), after cooling the precipitate collected and dried to give 10.4 g (74%) of the monohydro-chloride salt. It was dissolved in H2O (300 mL), NaHCO3 (2.4 g) added, stirred for 1 h and then the precipitate collected to give 9.0 g (61%) of a yellowish crystal powder, mp 295 °C (decomp.). pKa: 3.55, 10.30. 1H-NMR, (DMSO-d6): 0.98 (d, 3H, Me-C(6)), 1.05 (d, 3H, Me-C(7)), 3.65 (m, 1H, H-C(7)), 4.51 (m, 1H, H-C(6)), 6.08 (bs, 2H, NH2), 7.05 (s, 1H, H-N(8)), 7.30 (dd, 1H, nic-5), 7.75 (d, 1H, nic-4), 8.40 (d, 1H, nic-6), 8.60(s, 1H, nic-2), 9.70 (bs, H-N(3)). Anal. Calcd for C14H16N6O2 (300.3): C, 55.99; H, 5.37; N, 27.98. Found: C, 55.52; H, 5.47; N, 27.53.

6-Hydroxymethyl-5-nicotinoyl-5,6,7,8-tetrahydropterin (18): Analogous to procedure 16 with 14 (2.0 g, 4.5 mmol) in MeOH (100 mL) and Na (0.125 g). The resulting solid was recrystallized from EtOH/H2O to give 0.55 g (40%) of a yellowish crystal powder, mp 220-224 °C. pKa: 3.38, 10.30. 1H-NMR, (DMSO-d6): 3.12 (m, 2H, CH2), 3.35 (m, 1H, H-C(7)), 3.55 (m, 1H, H-C(7)), 4.59 (m, 1H, H-C(6)), 4.95 (t, 1H, OH), 6.08 (bs, 2H, NH2), 7.04 (s, 1H, H-N(8)), 7.28 (dd, 1H, nic-5), 7.75 (d, 1H, nic-4), 8.44 (d, 1H, nic-6), 8.55 (s, 1H, nic-2), 9.70 (bs, H-N(3)).; EtOH: 1.04 (t, 3H, CH3), 3.40 (m, 2H, CH2), 4.36 (1H, OH), Anal. Calcd for C13H14N6O3. EtOH (348.4): C, 51.72; H, 5.79; N, 24.12. Found: C, 51.67; H, 5.79; N, 24.01.

N2-Isobutyroyl-6-methyl-5-(1-methylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (19): A solution of 12 (2.06 g, 5.77 mmol) in abs. MeOH (200 mL) was treated with CH3I (20 mL) under stirring at rt for 4 days. The yellow solution was evaporated and the residue recrystallized from MeOH/H2O to give 1.88 g (55%). Further recrystallization from H2O (20 mL) yielded 1.3 g (45%) of yellowish crystals, mp 293 °C (decomp.). pKa: 8.77. 1H-NMR, (DMSO-d6): 1.02 (d, 6H, C(Me2), 1.08 (d, 3H, Me-C(6)), 2.72 (sept, 1H, H-CMe2), 3.32 (dd, 1H, H-C(7)), 3.62 (m. 1H, H-C(7)), 4.35 (s, 3H-Me-N), 4.85 (m, 1H, H-C(6)), 7.69 (s, 1H, H-N(8)), 7.99 (dd, 1H, nic-5), 8.57 (d, 1H, nic-4), 8.93 (d, 1H, nic-6), 9.36 (s, 1H, nic-2), 11.09 (s, H-N(3)), 11.43 (bs, 1H, H-N). Anal. Calcd for C18H23N6O3I (498.4): C, 43.39; H, 4.65; N, 16.86. Found: C, 43.09; H, 4.83; N, 16.66.

N2-Isobutyroyl-6,7-dimethyl-5-(1-methylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (20): Analogous to the preceding procedure with 13 (6.05 g, 16,3 mmol) in MeOH (700 mL) with CH3I (25 mL). After 5 days was concentrated to 100 mL, cooled and the precipitate collected to give after drying in a vacuum desiccator 5.65 g (66%) pure material, mp >300 °C. Recrystallization from H2O gave yellowish crystals. pK: 8.97. 1H-NMR, (DMSO-d6): 0.86 (d, 3H, Me-C(7)), 1.04 (d, 6H, C(Me2), 1.23 (d, 3H, Me-C(6)), 2.72 (sept, 1H, H-CMe2), 3.89 (m, 2H, H-C(7)), 4.31 (s, 3H, Me-N), 4.59 (m, 1H, H-C(6)), 7.18 (s, 1H, H-N(8)), 7.97 (dd, 1H, nic-5), 8.57 (d, 1H, nic-4), 8.86 (d, 1H, nic-6), 9.21 (s, 1H, nic-2), 11.15 (s, H-N(3)), 11.23 (bs, 1H, H-N). Anal. Calcd for C19H25N6O3I. 0.5 H2O (521.4): C, 43.77; H, 5.03; N, 16.12. Found: C, 43.65; H, 4.93; N, 16.33.

N2-Isobutyroyl-6-isobutyroyloxymethyl-5-(1-methylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (21): Analogous to the preceding procedure with 14 (0.975 g, 2.2 mmol) in abs. MeOH (80 mL) with CH3I (10 mL) for 2 days. After evaporation the oily residue was treated with little EtOAc to form a solid which was recrystallized from MeOH/EtOAc (1:4, 50 mL) to give 0.665 g (50 %) yellow needles and from the mother liquid 0.51 g (39%), mp 200 °C. pKa: 8.83. 1H-NMR, (DMSO-d6): 1.02 (d, 6H, C(Me2), 1.08 (d, 6H, C(Me2), 2.69 (sept, 1H, H-CMe2), 2.49 (sept, 1H, H-CMe2), 3.53 (dd, 1H, H-C(7)), 3.67 (dd, 1H, H-C(7)), 3.89 (dd, 1H, OCH2), 4.01 (dd, 1H, OCH2), 4.35 (s, 3H-Me-N), 4.96 (m, 1H, H-C(6)), 7.66 (s, 1H, H-N(8)), 7.96 (dd, 1H, nic-5), 8.57 (d, 1H, nic-4), 8.88 (d, 1H, nic-6), 9.22 (s, 1H, nic-2), 11.12 (s, H-N(3)), 11.39 (bs, 1H, H-N). Anal. Calcd for C22H29N6O5I . 0.75 H2O (597.9): C, 44.19; H, 5.14; N, 14.05. Found: C, 44.26; H, 5.14; N, 14.05.

N2-Isobutyroyl-6-methyl-5-(1-benzylnicotinoylium)-5,6,7,8-tetrahydropterin bromide (22): A solution of 12 (0.52 g, 1.46 mmol) in DMSO (15 mL) was treated with benzyl bromide (0.35 g, 2.04 mmol) for 18 h at rt. Evaporation at high vacuum to an orange oil, which was dissolved in MeOH (20 ml) and added dropwise with vigorous stirring into Et2O (80 mL). The precipitate was collected, washed with Et2O and recrystallized from little iPrOH to give 0.41 g (52%) yellow crystals, mp 235 °C. pKa: 8.87. 1H-NMR, (DMSO-d6): 0.98-1.12 (m, 9H, Me-C(6), C(Me2), 1.15 (d, 3H, Me-C(6)), 2.74 (sept, 1H, H-CMe2), 3.35 (m, 1H, H-C(7)), 3.62 (dd. 1H, H-C(7)), 4.82 (m, 1H, H-C(6)), 5.80 (dd, 2H, N-CH2), 7.36 (m, 5H, arom. H), 7.72 (s, 1H, H-N(8)), 8.08 (dd, 1H, nic-5), 8.69 (d, 1H, nic-4), 9.13 (d, 1H, nic-6), 9.47 (s, 1H, nic-2), 11.09 (s, H-N(3)), 11.43 (bs, 1H, H-N). Anal. Calcd for C24H27N6O3Br . 0.5 H2O (536.4): C, 53.74; H, 5.26; N, 15.67. Found: C, 53.66; H, 5.50; N, 15.27.

N2-Isobutyroyl-6,7-dimethyl-5-(1-benzylnicotinoylium)-5,6,7,8-tetrahydropterin bromide (23): Analogous to the preceding procedure with 13 (5.0 g, 13.5 mmol) and benzyl bromide (2.3 mL, 19.5 mmol) in DMSO (125 mL) for 12 h at rt. The crude product was recrystallized from MeOH (150 mL) to give 6.55 g (88%) yellowish crystals, mp 251 °C. pKa: 9.09. 1H-NMR, (DMSO-d6): 0.85 (d, 3H, Me-C(7)), 1.07 (d, 6H, Me2C), 1.22 (d, 3H, Me-C(6)), 2.78 (sept, 1H, H-CMe2), 3.93 (m, 1H, H-C(7)), 4.59 (m, 1H, H-C(6)), 5.81 (dd, 2H, N-CH2), 7.35 (m, 5H, arom. H), 7.65 (s, 1H, H-N(8)), 8.09 (dd, 1H, nic-5), 8.70 (d, 1H, nic-4), 9.15 (d, 1H, nic-6), 9.51 (s, 1H, nic-2), 10.99 (s, H-N(3)), 11.28 (bs, 1H, H-N). Anal. Calcd for C25H29N6O3Br . 0.5 H2O (550.4): C, 54.55; H, 5.49; N, 15.27. Found: C, 54.66; H, 5.63; N,
15.37.

N2-Isobutyroyl-6-isobutyroyloxymethyl)-5-(1-benzylnicotinoylium)-5,6,7,8-tetrahydropterin bromide (24): Analogous to the preceding prucedure with 14 (0.74 g, 1,67 mmol) and benzyl bromide (0.4 mL, 2.34 mmol) in DMSO (20 mL) for 18 h at rt. The crude product was recrystallized from EtOAc/MeOH to give 0.61 g (58 %) yellow crystals, mp 263 °C. pKa: 9.14. 1H-NMR, (DMSO-d6): 1.01-1.11 (m, 12H, 2 Me2C), 2.49 (sept, 1H, H-CMe2), 2.75 (sept, 1H, H-CMe2), 3.47 (m, 1H, H-C(7)), 3.61 (m, 1H, H-C(7)), 3.85 (dd, 1H, H2C-C(6)), 4.00 (dd, 1H, H2C-C(6)), 5.92 (dd, 2H, N-CH2), 7.33 (m, 5H, arom. H), 7.72 (s, 1H, H-N(8)), 8.10 (dd, 1H, nic-5), 8.67 (d, 1H, nic-4), 9.15 (d, 1H, nic-6), 9.45 (s, 1H, nic-2), 10.95 (s, H-N(3)), 11.44 (bs, 1H, H-N). Anal. Calcd for C28H33N6O5Br . 0.5 H2O (622.5): C, 54.02; H, 5.50; N, 13.50. Found: C, 54.07; H, 5.48; N, 13.51.

N2-Isobutyroyl-6,7-diphenyl-5-(1-benzylnicotinoylium)-5,6,7,8-tetrahydropterin bromide (25): Analogous to the preceding procedure with 15 (1.0 g, 2.02 mmol) and benzyl bromide (0.46 g, 2.7 mmol) in DMSO (20 mL) at 60 °C for 5 h. The crude product was recrystallized from MeOH/H2O (1:1, 150 mL) to give 1.1 g (79%) yellow needles, mp 269 °C. pKa: 9.09. 1H-NMR, (DMSO-d6): 1.10 (m, 6H, Me2C), 2.82 (sept, 1H, H-CMe2), 5.51 (d, 1H, H-C(7)), 3.88 (d, 1H, H-C(6)), 5.88 (dd, 2H, N-CH2), 7.03-7.44 (m, 10H, arom. H), 8.12 (dd, 1H, nic-5), 8.47 (s, 1H, H-N(8)), 8.78 (d, 1H, nic-4), 9.18 (d, 1H, nic-6), 9.66 (s, 1H, nic-2), 11.16 (s, H-N(3)), 11.47 (bs, 1H, H-N). Anal. Calcd for C35H33N6O5Br . H2O (683.6): C, 61.49; H, 5.16; N, 12.29. Found: C, 61.37; H, 5.61; N, 12.05.
N2-Isobutyroyl-6,7-dimethyl-5-(1-ethylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (26): Analogous to the preceding procedure with 13 (0.82 g, 2.2 mmol) and C2H5I (2 mL) in DMSO (10 mL) at rt for 2 days. The crude product was recrystallized from EtOH to give 0.8 g (67%) yellow crystals, mp 290 °C. pKa: 8.97. 1H-NMR, (DMSO-d6): 0.85 (d, 3H, Me-C(7)), 1.02 (d, 6H, C(Me2), 1.21 (d, 3H, Me-C(6)), 1.44 (t, 3H, H3C-CH2), 2.72 (sept, 1H, H-CMe2), 3.91 (m, 1H, H-C(7)), 4.62 (m, 3H, H2C-N, H-C(6)), 7.62 (s, 1H, H-N(8)), 8.00 (dd, 1H, nic-5), 8.60 (d, 1H, nic-4), 8.99 (d, 1H, nic-6), 9.39 (s, 1H, nic-2), 11.13 (s, H-N(3)), 11.23 (bs, 1H, H-N). Anal. Calcd for C20H27N6O3I . 0.5 H2O (535.4): C, 44.87; H, 5.27; N, 15.70. Found: C, 44.72; H, 5.32; N, 15.46.

N2-Isobutyroyl-6,7-dimethyl-5-(1-n-propylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (27):
Analogous to the preceding procedure with 13 (1.0 g, 2.7 mmol) and n-C3H7I (2 mL) in DMF (40 mL) at 100°C for 8 h. The reaction solution was evaporated, twice coevaporated with EtOH. The crude product was recrystallized from EtOH (30 mL) to give 1.1 g (72%) orange crystals, mp 288-290 °C (decomp.). pKa: 8.66. 1H-NMR, (DMSO-d6): 0.79 (t, 3H, H3C-CH2CH2), 0.91 (d, 3H, Me-C(7)), 1.01 (d, 6H, C(Me2), 1.21 (d, 3H, Me-C(6)), 1.44 (t, 3H, H3C-CH2), 1.81 (m, 2H, CH3CH2CH2), 2.72 (sept, 1H, H-CMe2), 3.91 (m, 1H, H-C(7)), 4.54 (m, 3H, H2C-N, H-C(6)), 7.64 (s, 1H, H-N(8)), 8.02 (dd, 1H, nic-5), 8.65 (d, 1H, nic-4), 8.98 (d, 1H, nic-6), 9.37 (s, 1H, nic-2), 11.15 (s, H-N(3)), 11.30 (bs, 1H, H-N). Anal. Calcd for C21H29N6O3I (540.4): C, 46.47; H, 5.41; N, 15.55. Found: C, 46.41; H, 5.46; N, 15.09.

N2-Isobutyroyl-6,7-dimethyl-5-(1-n-pentylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (28):
Analogous to the preceding procedure with 13 (1.04 g, 2.8 mmol) and n-C5H11I (0.7 g, 3.53 mmol) in DMF (40 mL) at 150 °C for 4 h. The reaction solution was evaporated, twice coevaporated with EtOH. The crude product was dissolved in little EtOH and dropwise added to stirring cold n-hexane (200 mL). The precipitate was collected and recrystallized from acetone to give 1.4 g (88 %) orange crystals, mp 255-257 °C. pKa: 8.68. 1H-NMR, (DMSO-d6): 0.78-1.01 (m, 10H, H3C-CH2CH2, Me-C(7)), 1.02 (d, 6H, C(Me2), 1.21 (d, 3H, Me-C(6)), 1.78 (t, 2H, H3C-CH2CH2CH2), 2.73 (sept, 1H, H-CMe2), 3.91 (m, 1H, H-C(7)), 4.56 (m, 3H, H2C-N, H-C(6)), 7.64 (s, 1H, H-N(8)), 8.04 (dd, 1H, nic-5), 8.64 (d, 1H, nic-4), 8.98 (d, 1H, nic-6), 9.33 (s, 1H, nic-2), 11.14 (s, H-N(3)), 11.27 (bs, 1H, H-N). Anal. Calcd for C23H33N6O3I (568.5): C, 48.60; H, 5.85; N, 14.78. Found: C, 48.11; H, 5.86; N, 14.77.

N2-Isobutyroyl-6,7-dimethyl-5-(1-n-octylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (29):
Analogous to the preceding procedure with 13 (1.0 g, 2.7 mmol) and n-C8H17I (1.0 g, 4.16 mmol) in DMF (40 mL) at 150 °C for 3 h. The reaction solution was evaporated, twice coevaporated with EtOH. The crude product was dissolved in little EtOH and dropwise added to stirring cold n-hexane (200 mL). The crude product was recrystallized from EtOAc/EtOH to give 1.15 g (70 %) orange crystals, mp 245-247 °C. pKa: 8.77. 1H-NMR, (DMSO-d6): 0.81-1.23 (m, 25H, H3C-(CH2,)5 Me-C(6), Me2C, Me-C(7)), 1.78 (m. 2H, H2C-H2C-N), 2.78 (sept, 1H, H-CMe2), 4.56 (m, 4H, H2C-N, H-C(7), H-C(6)), 7.63 (s, 1H, H-N(8)), 8.03 (dd, 1H, nic-5), 8.63 (d, 1H, nic-4), 8.98 (d, 1H, nic-6), 9.34 (s, 1H, nic-2), 11.14 (s, H-N(3)), 11.26 (bs, 1H, H-N). Anal. Calcd for C26H39N6O3I (610.6): C, 51.15; H, 6.44; N, 13.77. Found: C, 50.88; H, 6.34; N, 13.50.
N2-Isobutyroyl-6-methyl-5-(1-n-octylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (30):
Analogous to the preceding procedure with 12 (2.0 g, 5.6 mmol) and n-C8H17I (1.12 mL) in DMF (60 mL) at 150 °C for 6 h. The reaction solution was evaporated, twice coevaporated with EtOH. The crude product was heated with H2O (50 mL) and EtOH added till solution took place. Charcoal was added, filtered and the filtrate put in the icebox to get 1.52 g (46 %) yellow crystals, mp 203-205 °C. pKa: 8.92. 1H-NMR, (DMSO-d6): 0.83 (t, 3H, H3C(CH2)7), 1.00-1.23 (m, 19H, H3C-(CH2,)5 Me-C(6), Me2C), 1.77 (m. 2H, H2C-H2C-N), 2.69 (sept, 1H, H-CMe2), 3.34 (m, 1H, H-C(7)), 3.62 (m. 1H, H-C(7)), 4.56 (t, 2H, H2C-N), 4.83 (m, 1H, H-C(6)), 7.70 (s, 1H, H-N(8)), 8.03 (dd, 1H, nic-5), 8.62 (d, 1H, nic-4), 8.99 (d, 1H, nic-6), 9.34 (s, 1H, nic-2), 11.10 (s, H-N(3)), 11.41 (bs, 1H, H-N). Anal. Calcd for C25H37N6O3I . 0.5 H2O (605.6): C, 49.58; H, 6.32; N, 13.87. Found: C, 49.73; H, 6.31; N, 13.70.

N2-Isobutyroyl-6-isobutyroyloxymethyl-5-(1-n-octylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (31): Analogous to the preceding procedure with 14 (3.0 g, 6.78 mmol) and n-C8H17I (1.75 mL) in DMF (90 mL) at 150 °C for 4 h. The reaction solution was evaporated, twice coevaporated with EtOH and the residue dissolved in EtOAc (100 mL). Cooling overnight yielded 3.54 g (77%) crude material. Recrystallization from EtOAc/EtOH (5:4, 90 mL) gave 2.67 g (58%) yellow crystals, mp 235-236 °C. pKa: 8.95. 1H-NMR, (DMSO-d6): 0.83 (t, 3H, H3C(CH2)7), 1.00-1.23 (m, 16H, H3C-(CH2,)5, Me2C), 1.77 (m. 2H, H2C-H2C-N), 2.69 (sept, 1H, H-CMe2), 3.52 (m, 1H, H-C(7)), 3.65 (m. 1H, H-C(7)), 3.89 (dd, 1H, H2C-C(6)); 3.99 (dd, 1H, H2C-C(6)); 4.52 (t, 2H, H2C-N), 4.97 (m, 1H, H-C(6)), 7.69 (s, 1H, H-N(8)), 8.04 (dd, 1H, nic-5), 8.61 (d, 1H, nic-4), 8.98 (d, 1H, nic-6), 9.32 (s, 1H, nic-2), 11.08 (s, H-N(3)), 11.41 (bs, 1H, H-N). Anal. Calcd for C29H34N6O3I (682.6): C, 51.03; H, 6.35; N, 12.31. Found: C, 50.96; H, 6.39; N, 12.08.

6-Methyl-5-(1-n-octylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (32): A solution of 16 (0.5 g, 1.64 mmol) in DMF (10 mL) was treated with n-octyl iodide (0.38 mL) at 100 °C for 6 h. It was evaporated, coevaporated with EtOH and the residue recrystallized from EtOH/MeOH to give 0.6 g (67%) yellowish crystals, mp 206-208 °C. pKa: 1.09, 9.62. 1H-NMR, (DMSO-d6): 0.84 (t, 3H, H3C-(CH2)7), 0.97 (d, 3H, Me-C(6)), 1.01-1.24 (m, 10H, H3C-(CH2)5), 1.79 (m, 2H, N-CH2CH2), 3.23 (m, 1H, H-C(7)), 3.55 (m, 1H, H-C(7)), 4.57 (t, 2H, N-CH2), 4.77 (m, 1H, H-C(6)), 6.25 (bs, 2H, NH2), 7.33 (s, 1H, H-N(8)), 8.01 (dd, 1H, nic-5), 8.57 (d, 1H, nic-4), 8.97 (d, 1H, nic-6), 9.30 (s, 1H, nic-2), 9.80 (s, H-N(3)). Anal. Calcd for C21H31N6O2I (526.4): C, 47.92; H, 5.96; N, 15.96. Found: C, 47.76; H, 5.99; N, 15.94.

6,7-Dimethyl-5-(1-n-octylnicotinoylium)-5,6,7,8-tetrahydropterin iodide (33): Analogous to the preceding procedure with 17 (2.5 g, 8.3 mmol) in DMF (70 mL) and n-octyl iodide (1.85 mL) at 150 °C for 3 h. Recrystallization from EtOH (25 mL) yielded 3.94 g (79%) yellowish plates, mp 180 °C. pKa: 1.07, 9.81. 1H-NMR, (DMSO-d6): 0.83 (t, 3H, H3C-(CH2)7), 0.98 (d, 3H, Me-C(6)), 1.15 (d, 3H, Me-C(7)), 1.24 (m, 10H, H3C-(CH2)5), 1.79 (m, 2H, N-CH2CH2), 3.81 (m, 1H, H-C(7)), 4.56 (t, 2H, N-CH2), 4.57 (m, 1H, H-C(6)), 6.17 (bs, 2H, NH2), 7.32 (s, 1H, H-N(8)), 8.01 (dd, 1H, nic-5), 8.58 (d, 1H, nic-4), 8.95 (d, 1H, nic-6), 9.31 (s, 1H, nic-2), 9.80 (s, H-N(3)). Anal. Calcd for C22H33N6O2I . 0.5 H2O (549.6): C, 48.09; H, 6.24; N, 15.30. Found: C, 47.84; H, 6.43; N, 15.08.

6,7-Dimethyl-5-(1-benzylnicotinoylium)-5,6,7,8-tetrahydropterin bromide (34): Analogous to the preceding procedure with 17 (0.253 g, 0.84 mmol) in DMSO (10 mL) and benzyl bromide (0.1 g, 1.18 mmoL) at rt for 18 h. After evaporation in high vacuum the residue was recrystallized from EtOH (15 mL) to give 0.294 g (74%) of yellowish crystals, mp 275 °C (decomp.). pKa: 1.07, 9.81. 1H-NMR, (DMSO-d6): 0.83 (d, 3H, Me-C(7)), 1.15 (d, 3H, Me-C(6)), 3.85 (m, 1H, H-C(7)), 4.50 (m, 1H, H-C(6)), 5.84 (s, 2H, N-CH2), 6.31 (bs, 2H, NH2), 7.35 (m, 6H, arom. H, H-N(8)), 8.03 (dd, 1H, nic-5), 8.65 (d, 1H, nic-4), 9.06 (d, 1H, nic-6), 9.51 (s, 1H, nic-2), 9.82 (s, H-N(3)). Anal. Calcd for C21H23N6O2Br . 0.5 H2O (480.4): C, 52.51; H, 5.04; N, 17.50. Found: C, 52.53; H, 5.24; N, 16.84.

N2-Isobutyroyl-6-methyl-5-(1-benzyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (35): A solution of 22 (0.2 g, 0.37 mmol) and NaHCO3 (0.125 g) under N2-atmosphere was treated with EtOAc (6 mL). Under vigorous stirring Na2S2O4 (0.26 g, 1.5 mmol) was added in small portions and after 1 h the precipitate collected. The solid was washed with H2O, EtOAc and ether and dried in a vacuum desiccator to give 0.145 g (87%) crude material. Recrystallization from little EtOH yielded 0.086 g (52%) of a colorless powder, mp 210 °C. 1H-NMR, (DMSO-d6): 0.88 (m, 3H, Me-C(6)), 1.14 (d, 6H, Me2C), 2.74 (sept, 1H, H-CMe2), 2.93 (dd, 1H, nic-4'), 3.15 (dd, 1H, nic-4''), 3.19 (m, 2H, H-C(7)), 4.19 (s, 2H, N-CH2), 4.51 (m, 2H, H-C(6), nic-5), 5.84 (dd, 1H, nic-6), 6.30 (s, 1H, nic-2), 6.98 (s, 1H, H-N(8)), 7.15 (m, 5H, arom. H), 11.22 (s, H-N(3)), 11.24 (bs, 1H, H-N). Anal. Calcd for C24H28N6O3 (448.5): C, 64.27; H, 6.29; N, 18.74. Found: C, 63.83; H, 6,23; N, 18.58.

N2-Isobutyroyl-6,7-dimethyl-5-(1-benzyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (36): A solution of 23 (3.9 g, 7.2 mmol) and NaHCO3 (2.4 g, 28.8 mmol) in H2O (225 mL) was kept under N2-atmosphere. Under stirring Na2S2O4 (2.4 g, 28.8 mmol) was added in small portion within 15 min. and the resulting precipitate collected after 3 h. The crude material was recrystallized from abs. EtOH (200 mL) under nitrogen to give 1.41 g (42 %) of yellowish needles, mp 230 °C. 1H-NMR, (DMSO-d6): 0.75 (d, 3H, Me-C(7)), 1.12 (d, 6H, Me2C), 1.15 (d, 3H, Me-C(6)), 2.77 (sept, 1H, H-CMe2), 2.93 (dd, 1H, nic-4'), 3.15 (dd, 1H, nic-4''), 3.45 (m, 1H, H-C(7)), 4.14 (m, 3H, N-CH2, H-C(6)), 4.49 (m, 1H, nic-5), 5.84 (dd, 1H, nic-6), 6.31 (s, 1H, nic-2), 6.83 (s, 1H, H-N(8)), 7.15 (m, 5H, arom. H), 11.18 (m, H-N(3), H-N). Anal. Calcd for C25H30N6O3 . 0.5 H2O (471.6): C, 63.68; H, 6.63; N, 17.82. Found: C, 64.01; H, 6,48; N, 17.78.

N2-Isobutyroyl-6-isobutyroyloxymethyl-5-(1-benzyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (37): A solution of 24 (0.2 g, 0.32 mmol) and NaHCO3 (0.11 g, 1.3 mmol) in H2O (10 mL) was treated under N2-atmosphere and stirring with Na2S2O4 (0.226 g, 1.3 mmol) for 1 h at rt. The reaction solution was kept overnight in the icebox, the resulting precipitate was collected and recrystallized from little MeOH to yield 0.1 g (42%) of colorless crystals, mp 208 °C. 1H-NMR, (DMSO-d6): 1.02 (d, 6H, Me2C), 1.12 (d, 6H, Me2C), 2.48 (sept, 1H, H-CMe2), 2.74 (sept, 1H, H-CMe2), 2.94 (dd, 1H, nic-4'), 3.17 (dd, 1H, nic-4''), 3.76 (m, 2H, H-C(7)), 3.85 (dd, 2H, H2C-C(6)), 4.20 dd, 2H, N-CH2), 4.1 (m, 1H, nic-5), 4.55 (m, 1H, H-C(6)), 5.83 (dd, 1H, nic-6), 6.30 (s, 1H, nic-2), 7.00 (d, 1H, H-N(8)), 7.16 (m, 5H, arom. H), 11.26 (s, 1H, H-N(3)), 11.28 (s, 1H, H-N). Anal. Calcd for C28H34N6O5 . 0.5 H2O (543.6): C, 61.86; H, 6.49; N, 15.46. Found: C, 61.54; H, 6,22; N, 15.25.

N2-Isobutyroyl-6,7-dimethyl-5-(1-n-pentyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (38):
Analogous to the preceding procedure with 28 (0.25 g, 0.44 mmol) and NaHCO3 (0.15 g, 1.76 mmol) in H2O (10 mL) under N2-atmosophere. After successive addition of Na2S2O4 (0.306 g, 1.76 mmol) was stirred for 1 h, then cooled in the icebox and the precipitate collected after 6 h to give 62 mg (32%) of yellowish crystals, mp >200 °C (decomp.). 1H-NMR, (DMSO-d6): 0.84 (m. 6H, H3C(CH2)5, Me-C(7)), 1.11-1.19 (m, 15H, Me2C, Me-C(6), H3C(CH2)3), 2.74 (sept, 1H, H-CMe2), 2.90 (m, 3H, N-CH2, nic-4'), 3.11 (dd, 1H, nic-4''), 3.47 (m, 1H, H-C(7)), 4.20 (dd, 2H, H2C-C(6)), 4.45 (m, 1H, nic-5), 5.76 (dd, 1H, nic-6), 6.20 (s, 1H, nic-2), 6.89 (d, 1H, H-N(8)), 11.20 (bs, 2H, H-N(3), H-N). Anal. Calcd for C23H34N6O3 . 0.5 H2O (543.6): C, 61.86; H, 6.49; N, 15.46. Found: C, 61.54; H, 6,22; N, 15.25.

N2-Isobutyroyl-6,7-dimethyl-5-(1-n-octyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (39):
Analogous to the preceding procedure with 29 (0.25 g, 0.41 mmol) and NaHCO3 (0.15 g, 1.76 mmol) in H2O (10 mL) under N2-atmosphere. After successive addition of Na2S2O4 (0.285 g, 1.64 mmol) was stirred for 1 h, then cooled in the icebox and the precipitate collected after 4 h to give 0.10 g (50%) of yellowish crystals, mp > 200 °C (decomp.). 1H-NMR, (DMSO-d6): 0.79 (m. 6H, H3C(CH2)7, Me-C(7)), 1.02-1.26 (m, 21H, Me2C, Me-C(6), H3C(CH2)6), 2.74 (sept, 1H, H-CMe2), 2.90 (m, 3H, N-CH2, nic-4'), 3.07 (dd, 1H, nic-4''), 3.47 (m, 1H, H-C(7)), 4.18 (dd, 2H, H2C-C(6)), 4.45 (m, 1H, nic-5), 5.76 (dd, 1H, nic-6), 6.22 (s, 1H, nic-2), 6.88 (d, 1H, H-N(8)), 11.20 (bs, 2H, H-N(3), H-N). Anal. Calcd for C26H40N6O3 . 0.5 H2O (493.7): C, 63.26; H, 8.37; N, 17.02. Found: C, 62.94; H, 8.06; N, 17.12.

6-Methyl-5-(1-benzyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (40): A suspension of 35 (0.751 g, 1.67 mmol) in MeOH (40 mL) was treated under N2-atmosphere with K2CO3 (0.255 g, 1.84 mmol) at rt and stirring overnight. It was evaporated and the resulting oil recrystallized from H2O (15 mL) to give after drying in a vacuum desiccator 0.393 g (60%) of yellowish crystal powder, mp 232 °C. 1H-NMR, (DMSO-d6): 0.88 (d, 3H, Me-C(6)), 1.14 (d, 6H, Me2C), 2.88 (dd, 1H, nic-4'), 3.07 (dd, 1H, nic-4''), 3.09 (m, 2H, H-C(7)), 4.18 (s, 2H, N-CH2), 4.45 (m, 2H, H-C(6)), nic-5), 5.82 (d, 1H, nic-6), 6.28 (bs, 2H, NH2), 6.32 (s, 1H, nic-2), 6.57 (s, 1H, H-N(8)), 7.25 (m, 5H, arom. H), 10.5 (bs, H-N(3)). Anal. Calcd for C20H22N6O2 . H2O (396.5): C, 60.59; H, 6.10; N, 21.20. Found: C, 60.34; H, 6,12; N, 20.93.

6,7-Dimethyl-5-(1-benzyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (41): Analogous to the preceding procedure with 36 (2.51 g, 4,55 mmol) in MeOH (110 mL) under N2-atmosphere with K2CO3 (0.6.85 g, 0.49 mmol) at rt and stirring overnight. The resulting precipitate gave after drying in a vacuum desiccator 1.42 g (72%) analytically pure yellowish crystals, mp 255 °C. 1H-NMR, (DMSO-d6): 0.75 (d, 3H, Me-C(6)), 1.02 (d, 3H, Me-C(6)), 2.90 (dd, 1H, nic-4'), 3.10 (dd, 1H, nic-4''), 3.35 (1H, H-C(7)), 4.13 (m. 1H, H-C(6)), 4.16 (dd, 2H, N-CH2), 4.45 (m, 1H, nic-5), 5.84 (d, 1H, nic-6), 6.04 (bs, 2H, NH2), 6.31 (s, 1H, nic-2), 6.52 (s, 1H, H-N(8)), 7.25 (m, 5H, arom. H), 9.80 (bs, H-N(3)). Anal. Calcd for C21H24N6O2 (392.5): C, 64.27; H, 6.16; N, 21.41. Found: C, 63.95; H, 6,123; N, 21.33.

6-Hydroxymethyl-5-(1-benzyl-1,4-dihydronicotinoyl)-5,6,7,8-tetrahydropterin (42): Analogous to the preceding procedure with 37 (0.22 g, 0.41 mmol) and K2CO3 (66 mg) in MeOH (12 mL). It was evaporated and the residue recrystallized from H2O (5 mL) to give 94 mg (53%) of yellowish crystals, mp 210 °C. 1H-NMR, (DMSO-d6): 2.89 (dd, 1H, nic-4'), 3.09 (m, 2H, H-C(7)), 3.12 (dd, 1H, nic-4''), 3.49 (m, 2H, H2C-C(6)), 4.17 (s, 2H, N-CH2), 4.25 (m, 2H, H-C(6)), 4.45 (dt, 1H, nic-5), 5.80 (d, 1H, nic-6), 6.04 (bs, 2H, NH2), 6.44 (s, 1H, nic-2), 6.61 (s, 1H, H-N(8)), 7.25 (m, 5H, arom. H), 10.1 (bs, H-N(3)). Anal. Calcd for C20H22N6O3 . 2 H2O (430.5): C, 55.81; H, 6.09; N, 19.52. Found: C, 55.64; H, 5.86; N, 18.92.

Dedicated to Professor Emeritus Keiichiro Fukumoto on the occasion of his 75th birthday

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