2.1 General

Ultraviolet–visible (UV–Vis) absorption and CD spectra were measured with Hitachi U-4100 (Tokyo, Japan) and JASCO J-1500 spectrometers (Hachioji, Japan), respectively. 1H NMR spectra were measured at room temperature with a JEOL ECA-600 (600 MHz) or AL400 (400 MHz) spectrometer (Akishima, Japan); chemical shifts (δs) are expressed in parts per million relative to residual chloroform (δ = 7.26 ppm) as an internal reference. Proton peaks were assigned using 1H–1H two-dimensional NMR techniques. High resolution mass spectra (HRMS) were recorded on a Bruker micrOTOF II spectrometer (Billerica, MA, USA): atmospheric pressure chemical ionization (APCI) and positive mode in acetonitrile. Flash column chromatography (FCC) was carried out with silica gel (Merck Kieselgel 60, 0.040–0.063 mm, Darmstadt, Germany). HPLC was performed on a packed octadecylated column (Inertsil ODS-P 5 μm, 10 mmϕ × 250 mm, GL Sciences, Tokyo, Japan) with Shimadzu LC-20AR pumps and SPD-M20A photodiode-array detector (Kyoto, Japan).

Pyropheophorbide-a (6) [59, 60] and its methyl ester (7) [61,62,63,64] were prepared according to reported procedures. All the reaction reagents and solvents were obtained from commercial suppliers and utilized as supplied. Especially, chiral methylcarbinols were purchased from TCI (Tokyo, Japan). Dry dichloromethane for esterification was obtained from FUJIFILM Wako Pure Chem. (Osaka, Japan) as reagent for organic synthesis as super dehydrated grade. Distilled water was prepared by a Yamato AutoStill WG250 system (Tokyo, Japan). Triton X-100 was purchased from Nacalai Tesque (Kyoto, Japan) and used as received. For optical spectroscopy, tetrahydrofuran (THF) was purchased from Nacalai Tesque as reagent prepared specially for HPLC.

2.2 Synthesis of pyropheophorbides-a 5aR/S–5cR/S

Carboxylic acid 6 (240.6 mg, 450 μmol) was dissolved into dry dichloromethane (30 ml) in the dark under argon at room temperature. The solution was cooled down in an ice bath, to which chiral methylcarbinol (2.25 mmol, 5 eq.), 1-[3-(N,N-dimethylamino)propyl]-3-ethylcarbodiimide hydrogen chloride (EDC·HCl, 431.3 mg, 2.25 mmol, 5 eq.), and 4-(N,N-dimethylamino)pyridine (DMAP, 549.8 mg, 4.5 mmol, 10 eq.) were added and stirred for 15 min. The mixed solution was further stirred for 15 h at room temperature. The reaction mixture was washed with an aqueous 1% hydrogen chloride solution, an aqueous solution saturated with sodium hydrogen carbonate, and brine, dried over sodium sulfate, and filtered. All the solvent was evaporated, and the residue was purified by FCC with dichloromethane and 0–3% diethyl ether to give the corresponding ester 5.

(R)-2-Butyl pyropheophorbide-a (5aR): Esterification of 6 with (R)-2-butanol (206.9 μl) gave the titled ester (194.1 mg, 329 μmol, 73%): black solid; mp 199–200 °C; VIS (CH2Cl2) λmax/nm = 668 (relative intensity, 0.43), 610 (0.08), 560 (0.03), 539 (0.09), 508 (0.11), 476 (0.04), 414 (1.00), 399 (0.81), 379 (0.54), 321 (0.22); 1H NMR (CDCl3, 600 MHz) δ/ppm = 9.45 (1H, s, 10-H), 9.33 (1H, s, 5-H), 8.55 (1H, s, 20-H), 7.98 (1H, dd, J = 18, 11.5 Hz, 31-H), 6.25 (1H, dd, J = 18, 1 Hz, 32-H trans to C31–H), 6.15 (1H, dd, J = 11.5, 1 Hz, 32-H cis to C31–H), 5.27, 5.11 (each 1H, d, J = 20 Hz, 131-CH2), 4.81 (1H, sextet, J = 6 Hz, 172-COOCH), 4.50 (1H, dq, J = 2, 7 Hz, 18-H), 4.30 (1H, dt, J = 9, 2 Hz, 17-H), 3.65 (3H, s, 12-CH3), 3.64 (2H, q, J = 8 Hz, 8-CH2), 3.40 (3H, s, 2-CH3), 3.20 (3H, s, 7-CH3), 2.74–2.65, 2.58–2.49 (each 1H, m, 171-CH2), 2.35–2.22 (2H, m, 17-CH2), 1.81 (3H, d, J = 7 Hz, 18-CH3), 1.68 (3H, t, J = 8 Hz, 81-CH3), 1.52–1.39 (2H, m, 172-COOCCH2), 1.15 (3H, d, J = 6 Hz, 172-COOCCH3), 0.78 (3H, t, J = 7 Hz, 172-COOC2CH3), − 0.09, − 2.04 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 591.3326, calcd. for C37H43N4O3: MH+, 591.3330.

(S)-2-Butyl pyropheophorbide-a (5aS): Esterification of 6 with (S)-2-butanol (206.9 μl) gave the titled ester (186.1 mg, 315 μmol, 70%): black solid; mp 200–201 °C; VIS (CH2Cl2) λmax/nm = 668 (relative intensity, 0.43), 610 (0.08), 561 (0.03), 539 (0.09), 510 (0.10), 475 (0.04), 414 (1.00), 399 (0.81), 378 (0.53), 322 (0.20); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.44 (1H, s, 10-H), 9.33 (1H, s, 5-H), 8.55 (1H, s, 20-H), 7.98 (1H, dd, J = 18, 11 Hz, 31-H), 6.27 (1H, dd, J = 18, 1 Hz, 32-H trans to C31–H), 6.16 (1H, dd, J = 11, 1 Hz, 32-H cis to C31–H), 5.28, 5.12 (each 1H, d, J = 20 Hz, 131-CH2), 4.86 (1H, sextet, J = 6 Hz, 172-COOCH), 4.51 (1H, dq, J = 2, 7 Hz, 18-H), 4.30 (1H, dt, J = 7, 2 Hz, 17-H), 3.65 (3H, s, 12-CH3), 3.64 (2H, q, J = 8 Hz, 8-CH2), 3.40 (3H, s, 2-CH3), 3.20 (3H, s, 7-CH3), 2.77–2.66, 2.61–2.49 (each 1H, m, 171-CH2), 2.34–2.22 (2H, m, 17-CH2), 1.83 (3H, d, J = 7 Hz, 18-CH3), 1.67 (3H, t, J = 8 Hz, 81-CH3), 1.53 (2H, m, 172-COOCCH2), 1.15 (3H, d, J = 6 Hz, 172-COOCCH3), 0.84 (3H, t, J = 7 Hz, 172-COOC2CH3), 0.42, − 1.72 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 591.3320, calcd. for C37H43N4O3: MH+, 591.3330.

(R)-2-Octyl pyropheophorbide-a (5bR): Esterification of 6 with (R)-2-octanol (357.3 μl) gave the titled ester (203.8 mg, 315 μmol, 70%): black solid; mp 66–67 °C; VIS (CH2Cl2) λmax/nm = 668 (relative intensity, 0.43), 609 (0.08), 561 (0.04), 539 (0.10), 510 (0.12), 477 (0.06), 414 (1.00), 399 (0.81), 379 (0.55), 321 (0.24); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.45 (1H, s, 10-H), 9.34 (1H, s, 5-H), 8.55 (1H, s, 20-H), 7.98 (1H, dd, J = 18, 12 Hz, 31-H), 6.26 (1H, dd, J = 18, 1 Hz, 32-H trans to C31–H), 6.16 (1H, dd, J = 12, 1 Hz, 32-H cis to C31–H), 5.28, 5.11 (each 1H, d, J = 20 Hz, 131-CH2), 4.86 (1H, sextet, J = 6 Hz, 172-COOCH), 4.50 (1H, dq, J = 2, 7 Hz, 18-H), 4.30 (1H, dt, J = 8, 2 Hz, 17-H), 3.65 (3H, s, 12-CH3), 3.65 (2H, q, J = 8 Hz, 8-CH2), 3.40 (3H, s, 2-CH3), 3.20 (3H, s, 7-CH3), 2.75–2.64, 2.58–2.47 (each 1H, m, 171-CH2), 2.35–2.20 (2H, m, 17-CH2), 1.81 (3H, d, J = 7 Hz, 18-CH3), 1.67 (3H, t, J = 8 Hz, 81-CH3), 1.51–1.41, 1.41–1.31 (each 1H, m, 172-COOCCH2), 1.26–1.18 (8H, m, 172-COOC2(CH2)4), 1.15 (3H, d, J = 6 Hz, 172-COOCCH3), 0.80 (3H, t, J = 7 Hz, 172-COOC6CH3), 0.42, − 1.73 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 647.3977, calcd. for C41H51N4O3: MH+, 647.3956.

(S)-2-Octyl pyropheophorbide-a (5bS): Esterification of 6 with (S)-2-octanol (357.3 μl) gave the titled ester (212.5 mg, 328 μmol, 73%): black solid; mp 67–68 °C; VIS (CH2Cl2) λmax/nm = 668 (relative intensity, 0.44), 610 (0.08), 560 (0.03), 539 (0.09), 509 (0.10), 476 (0.04), 414 (1.00), 400 (0.81), 380 (0.54), 323 (0.20); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.46 (1H, s, 10-H), 9.35 (1H, s, 5-H), 8.56 (1H, s, 20-H), 7.99 (1H, dd, J = 18, 12 Hz, 31-H), 6.27 (1H, dd, J = 18, 1 Hz, 32-H trans to C31–H), 6.16 (1H, dd, J = 12, 1 Hz, 32-H cis to C31–H), 5.28, 5.12 (each 1H, d, J = 20 Hz, 131-CH2), 4.90 (1H, sextet, J = 6 Hz, 172-COOCH), 4.51 (1H, dq, J = 2, 7 Hz, 18-H), 4.30 (1H, dt, J = 8, 2 Hz, 17-H), 3.66 (3H, s, 12-CH3), 3.66 (2H, q, J = 8 Hz, 8-CH2), 3.41 (3H, s, 2-CH3), 3.22 (3H, s, 7-CH3), 2.75–2.65, 2.60–2.50 (each 1H, m, 171-CH2), 2.33–2.22 (2H, m, 17-CH2), 1.82 (3H, d, J = 7 Hz, 18-CH3), 1.68 (3H, t, J = 8 Hz, 81-CH3), 1.56–1.47, 1.46–1.35 (each 1H, m, 172-COOCCH2), 1.28–1.08 (8H, m, 172-COOC2(CH2)4), 1.14 (3H, d, J = 7 Hz, 172-COOCCH3), 0.82 (3H, t, J = 7 Hz, 172-COOC6CH3), 0.44, − 1.71 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 647.3955, calcd. for C41H51N4O3: MH+, 647.3956.

(R)-1-Phenylethyl pyropheophorbide-a (5cR): Esterification of 6 with (R)-1-phenylethanol (269.5 μl) gave the titled ester (224.2 mg, 351 μmol, 78%): black solid; mp 86–87 °C; VIS (CH2Cl2) λmax/nm = 668 (relative intensity, 0.44), 610 (0.08), 559 (0.03), 539 (0.09), 509 (0.10), 477 (0.04), 414 (1.00), 400 (0.81), 380 (0.54), 323 (0.21); 1H NMR (CDCl3, 600 MHz) δ/ppm = 9.50 (1H, s, 10-H), 9.39 (1H, s, 5-H), 8.54 (1H, s, 20-H), 8.01 (1H, dd, J = 18, 11 Hz, 31-H), 7.29–7.22 (5H, m, 172-COOCC6H5), 6.29 (1H, dd, J = 18, 1 Hz, 32-H trans to C31–H), 6.17 (1H, dd, J = 11, 1 Hz, 32-H cis to C31–H), 5.88 (1H, q, J = 6 Hz, 172-COOCH), 5.22, 5.05 (each 1H, d, J = 19 Hz, 131-CH2), 4.47 (1H, br-q, J = 7 Hz, 18-H), 4.27 (1H, br-d, J = 9 Hz, 17-H), 3.69 (2H, q, J = 8 Hz, 8-CH2), 3.67 (3H, s, 12-CH3), 3.41 (3H, s, 2-CH3), 3.24 (3H, s, 7-CH3), 2.72–2.67, 2.60–2.55 (each 1H, m, 171-CH2), 2.31–2.25 (2H, m, 17-CH2), 1.78 (3H, d, J = 7 Hz, 18-CH3), 1.70 (3H, t, J = 8 Hz, 81-CH3), 1.49 (3H, d, J = 6 Hz, 172-COOCCH3), 0.45, − 1.69 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 639.3325, calcd. for C41H43N4O3: MH+, 639.3330.

(S)-1-Phenylethyl pyropheophorbide-a (5cS): Esterification of 6 with (S)-1-phenylethanol (269.5 μl) gave the titled ester (253.0 mg, 396 μmol, 88%): black solid; mp 87–88 °C; VIS (CH2Cl2) λmax/nm = 668 (relative intensity, 0.44), 610 (0.08), 559 (0.03), 540 (0.09), 510 (0.10), 477 (0.04), 415 (1.00), 400 (0.80), 379 (0.53), 322 (0.21); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.46 (1H, s, 10-H), 9.35 (1H, s, 5-H), 8.52 (1H, s, 20-H), 7.99 (1H, dd, J = 18, 12 Hz, 31-H), 7.28–7.21 (5H, m, 172-COOCC6H5), 6.27 (1H, dd, J = 18, 1 Hz, 32-H trans to C31–H), 6.16 (1H, dd, J = 12, 1 Hz, 32-H cis to C31–H), 5.86 (1H, q, J = 7 Hz, 172-COOCH), 5.24, 5.07 (each 1H, d, J = 20 Hz, 131-CH2), 4.45 (1H, dq, J = 2, 7 Hz, 18-H), 4.26 (1H, dt, J = 8, 2 Hz, 17-H), 3.66 (2H, q, J = 7 Hz, 8-CH2), 3.66 (3H, s, 12-CH3), 3.39 (3H, s, 2-CH3), 3.21 (3H, s, 7-CH3), 2.71–2.63, 2.58–2.50 (each 1H, m, 171-CH2), 2.35–2.21 (2H, m, 17-CH2), 1.77 (3H, d, J = 7 Hz, 18-CH3), 1.68 (3H, t, J = 7 Hz, 81-CH3), 1.42 (3H, d, J = 7 Hz, 172-COOCCH3), 0.43, − 1.75 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 639.3345, calcd. for C41H43N4O3: MH+, 639.3330.

2.3 Synthesis of pyropheophorbides-d 4aR/S–4cR/S

Olefin 5 (350 μmol) was dissolved into THF (50 ml) in the dark under nitrogen at room temperature, to which one piece of osmium tetroxide, distilled water (1 ml), sodium periodate (374.3 mg, 1.75 mmol), and acetic acid (1 ml) were added. After stirred for 15 h, the reaction mixture was diluted with dichloromethane (50 ml), washed with an aqueous solution saturated with sodium hydrogen carbonate and distilled water, dried over sodium sulfate, and filtered. All the solvents were evaporated, and the residue was purified by FCC with dichloromethane and 0–3% diethyl ether to give the corresponding aldehyde 4.

(R)-2-Butyl pyropheophorbide-d (4aR): Oxidation of 5aR (206.8 mg) gave the titled aldehyde (116.2 mg, 196 μmol, 56%): black solid; mp 114–115 °C; VIS (CH2Cl2) λmax/nm = 695 (relative intensity, 0.80), 634 (0.09), 555 (0.16), 522 (0.14), 428 (1.00), 388 (0.84), 328 (0.28), 306 (0.29); 1H NMR (CDCl3, 600 MHz) δ/ppm = 11.48 (1H, s, 3-CHO), 10.17 (1H, s, 5-H), 9.49 (1H, s, 10-H), 8.81 (1H, s, 20-H), 5.34, 5.19 (each 1H, d, J = 19 Hz, 131-CH2), 4.82 (1H, sextet, J = 6 Hz, 172-COOCH), 4.59 (1H, dq, J = 2, 8 Hz, 18-H), 4.39 (1H, dt, J = 9, 2 Hz, 17-H), 3.74 (3H, s, 2-CH3), 3.67 (3H, s, 12-CH3), 3.66, 3.62 (each 1H, dq, J = 15, 8 Hz, 8-CH2), 3.23 (3H, s, 7-CH3), 2.76–2.70, 2.60–2.53 (each 1H, m, 171-CH2), 2.33–2.26 (2H, m, 17-CH2), 1.86 (3H, d, J = 8 Hz, 18-CH3), 1.67 (3H, t, J = 8 Hz, 81-CH3), 1.52–1.39 (2H, m, 172-COOCCH2), 1.16 (3H, d, J = 6 Hz, 172-COOCCH3), 0.77 (3H, t, J = 8 Hz, 172-COOC2CH3), − 0.27, − 2.19 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 593.3134, calcd. for C36H41N4O4: MH+, 593.3122.

(S)-2-Butyl pyropheophorbide-d (4aS): Oxidation of 5aS (206.8 mg) gave the titled aldehyde (190.9 mg, 322 μmol, 92%): black solid; mp 111–112 °C; VIS (CH2Cl2) λmax/nm = 695 (relative intensity, 0.77), 636 (0.11), 555 (0.17), 523 (0.16), 427 (1.00), 387 (0.90), 329 (0.35), 307 (0.35); 1H NMR (CDCl3, 400 MHz) δ/ppm = 11.48 (1H, s, 3-CHO), 10.16 (1H, s, 5-H), 9.48 (1H, s, 10-H), 8.81 (1H, s, 20-H), 5.35, 5.19 (each 1H, d, J = 20 Hz, 131-CH2), 4.86 (1H, sextet, J = 6 Hz, 172-COOCH), 4.59 (1H, dq, J = 2, 7 Hz, 18-H), 4.38 (1H, dt, J = 9, 2 Hz, 17-H), 3.75 (3H, s, 2-CH3), 3.67 (3H, s, 12-CH3), 3.63 (2H, q, J = 8 Hz, 8-CH2), 3.23 (3H, s, 7-CH3), 2.80–2.69, 2.64–2.54 (each 1H, m, 171-CH2), 2.35–2.22 (2H, m, 17-CH2), 1.86 (3H, d, J = 7 Hz, 18-CH3), 1.67 (3H, t, J = 8 Hz, 81-CH3), 1.63–1.43 (2H, m, 172-COOCCH2), 1.15 (3H, d, J = 6 Hz, 172-COOCCH3), 0.85 (3H, t, J = 7 Hz, 172-COOC2CH3), − 0.27, − 2.20 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 593.3132, calcd. for C36H41N4O4: MH+, 593.3122.

(R)-2-Octyl pyropheophorbide-d (4bR): Oxidation of 5bR (226.4 mg) gave the titled aldehyde (165.8 mg, 256 μmol, 73%): black solid; mp 83–84 °C; VIS (CH2Cl2) λmax/nm = 695 (relative intensity, 0.77), 635 (0.10), 555 (0.17), 522 (0.16), 428 (1.00), 388 (0.88), 329 (0.37), 307 (0.35); 1H NMR (CDCl3, 400 MHz) δ/ppm = 11.50 (1H, s, 3-CHO), 10.21 (1H, s, 5-H), 9.52 (1H, s, 10-H), 8.82 (1H, s, 20-H), 5.35, 5.19 (each 1H, d, J = 20 Hz, 131-CH2), 4.87 (1H, sextet, J = 6 Hz, 172-COOCH), 4.59 (1H, dq, J = 2, 7 Hz, 18-H), 4.38 (1H, dt, J = 9, 2 Hz, 17-H), 3.76 (3H, s, 2-CH3), 3.68 (3H, s, 12-CH3), 3.66 (2H, q, J = 8 Hz, 8-CH2), 3.25 (3H, s, 7-CH3), 2.78–2.68, 2.63–2.49 (each 1H, m, 171-CH2), 2.36–2.22 (2H, m, 17-CH2), 1.86 (3H, d, J = 7 Hz, 18-CH3), 1.68 (3H, t, J = 8 Hz, 81-CH3), 1.51–1.41, 1.40–1.30 (each 1H, m, 172-COOCCH2), 1.24–1.12 (8H, m, 172-COOC2(CH2)4), 1.16 (3H, d, J = 6 Hz, 172-COOCCH3), 0.81 (3H, t, J = 7 Hz, 172-COOC6CH3), − 0.23, − 2.16 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 649.3730, calcd. for C40H49N4O4: MH+, 649.3748.

(S)-2-Octyl pyropheophorbide-d (4bS): Oxidation of 5bS (226.4 mg) gave the titled aldehyde (168.1 mg, 259 μmol, 74%): black solid; mp 89–90 °C; VIS (CH2Cl2) λmax/nm = 695 (relative intensity, 0.81), 633 (0.09), 555 (0.16), 522 (0.15), 429 (1.00), 388 (0.84), 329 (0.30), 308 (0.31); 1H NMR (CDCl3, 400 MHz) δ/ppm = 11.48 (1H, s, 3-CHO), 10.17 (1H, s, 5-H), 9.49 (1H, s, 10-H), 8.82 (1H, s, 20-H), 5.35, 5.19 (each 1H, d, J = 20 Hz, 131-CH2), 4.91 (1H, sextet, J = 6 Hz, 172-COOCH), 4.59 (1H, br-q, J = 7 Hz, 18-H), 4.38 (1H, br-d, J = 8 Hz, 17-H), 3.75 (3H, s, 2-CH3), 3.67 (3H, s, 12-CH3), 3.63 (2H, q, J = 8 Hz, 8-CH2), 3.23 (3H, s, 7-CH3), 2.80–2.68, 2.64–2.52 (each 1H, m, 171-CH2), 2.35–2.22 (2H, m, 17-CH2), 1.86 (3H, d, J = 7 Hz, 18-CH3), 1.67 (3H, t, J = 8 Hz, 81-CH3), 1.56–1.48, 1.47–1.36 (each 1H, m, 172-COOCCH2), 1.29–1.16 (8H, m, 172-COOC2(CH2)4), 1.14 (3H, d, J = 6 Hz, 172-COOCCH3), 0.82 (3H, t, J = 7 Hz, 172-COOC6CH3), − 0.27, − 2.19 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 649.3728, calcd. for C40H49N4O4: MH+, 649.3748.

(R)-1-Phenylethyl pyropheophorbide-d (4cR): Oxidation of 5cR (223.6 mg) gave the titled aldehyde (172.7 mg, 270 μmol, 77%): black solid; mp 121–122 °C; VIS (CH2Cl2) λmax/nm = 695 (relative intensity, 0.79), 635 (0.09), 555 (0.17), 522 (0.16), 488 (0.08), 430 (1.00), 388 (0.85), 329 (0.34), 306 (0.36); 1H NMR (CDCl3, 600 MHz) δ/ppm = 11.50 (1H, s, 3-CHO), 10.21 (1H, s, 5-H), 9.52 (1H, s, 10-H), 8.81 (1H, s, 20-H), 7.30–7.23 (5H, m, 172-COOCC6H5), 5.90 (1H, q, J = 7 Hz, 172-COOCH), 5.29, 5.13 (each 1H, d, J = 20 Hz, 131-CH2), 4.57 (1H, dq, J = 2, 7 Hz, 18-H), 4.36 (1H, dt, J = 9, 2 Hz, 17-H), 3.76 (3H, s, 2-CH3), 3.68 (3H, s, 12-CH3), 3.66, 3.64 (each 1H, dq, J = 13, 8 Hz, 8-CH2), 3.26 (3H, s, 7-CH3), 2.76–2.70, 2.65–2.60 (each 1H, m, 171-CH2), 2.34–2.25 (2H, m, 17-CH2), 1.84 (3H, d, J = 7 Hz, 18-CH3), 1.70 (3H, t, J = 8 Hz, 81-CH3), 1.52 (3H, d, J = 7 Hz, 172-COOCCH3), − 0.25, − 2.17 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 641.3101, calcd. for C40H41N4O4: MH+, 641.3122.

(S)-1-Phenylethyl pyropheophorbide-d (4cS): Oxidation of 5cS (223.6 mg) gave the titled aldehyde (168.2 mg, 262 μmol, 75%): black solid; mp 120–121 °C; VIS (CH2Cl2) λmax/nm = 695 (relative intensity, 0.81), 635 (0.09), 555 (0.16), 522 (0.15), 488 (0.06), 430 (1.00), 388 (0.84), 329 (0.30), 307 (0.31); 1H NMR (CDCl3, 400 MHz) δ/ppm = 11.49 (1H, s, 3-CHO), 10.20 (1H, s, 5-H), 9.52 (1H, s, 10-H), 8.79 (1H, s, 20-H), 7.28–7.22 (5H, m, 172-COOCC6H5), 5.87 (1H, q, J = 6 Hz, 172-COOCH), 5.31, 5.13 (each 1H, d, J = 20 Hz, 131-CH2), 4.53 (1H, dq, J = 2, 8 Hz, 18-H), 4.35 (1H, dt, J = 7, 2 Hz, 17-H), 3.74 (3H, s, 2-CH3), 3.68 (3H, s, 12-CH3), 3.66 (2H, q, J = 8 Hz, 8-CH2), 3.25 (3H, s, 7-CH3), 2.75–2.66, 2.63–2.53 (each 1H, m, 171-CH2), 2.34–2.24 (2H, m, 17-CH2), 1.81 (3H, d, J = 8 Hz, 18-CH3), 1.68 (3H, t, J = 8 Hz, 81-CH3), 1.43 (3H, d, J = 6 Hz, 172-COOCCH3), − 0.24, − 2.18 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 641.3099, calcd. for C40H41N4O4: MH+, 641.3122.

2.4 Synthesis of 3-hydroxymethyl-pyropheophorbides-a 3aR/S–3cR/S

Aldehyde 4 (200 μmol) was dissolved into dichloromethane (20 ml) in the dark under nitrogen at room temperature, to which tert-butylamine borane complex (69.6 mg, 800 μmol) was added. After stirred for 15 min, the reaction mixture was diluted with dichloromethane (50 ml), washed with an aqueous solution saturated with ammonium chloride, dried over sodium sulfate, and filtered. All the solvent was evaporated, and the residue was purified by FCC with dichloromethane and 0–2% methanol to give the corresponding alcohol 3.

(R)-2-Butyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (3aR): Reduction of 4aR (118.5 mg) gave the titled alcohol (73.7 mg, 124 μmol, 62%): black solid; mp 249–250 °C; VIS (CH2Cl2) λmax/nm = 663 (relative intensity, 0.48), 605 (0.08), 557 (0.04), 535 (0.10), 505 (0.11), 471 (0.05), 410 (1.00), 397 (0.80), 376 (0.57), 317 (0.22); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.29 (1H, s, 5-H), 9.18 (1H, s, 10-H), 8.47 (1H, s, 20-H), 5.75 (2H, s, 3-CH2), 5.05, 4.93 (each 1H, d, J = 20 Hz, 131-CH2), 4.83 (1H, sextet, J = 6 Hz, 172-COOCH), 4.39 (1H, dq, J = 2, 7 Hz, 18-H), 4.12 (1H, dt, J = 9, 2 Hz, 17-H), 3.56 (2H, q, J = 8 Hz, 8-CH2), 3.45 (3H, s, 12-CH3), 3.34 (3H, s, 2-CH3), 3.17 (3H, s, 7-CH3), 2.57–2.44 (2H, m, 171-CH2), 2.27–2.17, 2.13–2.02 (each 1H, m, 17-CH2), 1.72 (3H, d, J = 7 Hz, 18-CH3), 1.61 (3H, t, J = 8 Hz, 81-CH3), 1.55–1.39 (2H, m, 172-COOCCH2), 1.16 (3H, d, J = 6 Hz, 172-COOCCH3), 0.80 (3H, t, J = 7 Hz, 172-COOC2CH3), − 0.09, − 2.04 (each 1H, br-s, NH × 2) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 595.3279 calcd. for C36H43N4O4: MH+, 595.3279.

(S)-2-Butyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (3aS): Reduction of 4aS (118.5 mg) gave the titled alcohol (91.6 mg, 154 μmol, 77%): black solid; mp 217–218 °C; VIS (CH2Cl2) λmax/nm = 662 (relative intensity, 0.48), 605 (0.08), 559 (0.03), 536 (0.09), 506 (0.10), 471 (0.04), 410 (1.00), 395 (0.79), 376 (0.57), 318 (0.21); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.37 (1H, s, 5-H), 9.34 (1H, s, 10-H), 8.52 (1H, s, 20-H), 5.83 (2H, s, 3-CH2), 5.15, 5.02 (each 1H, d, J = 20 Hz, 131-CH2), 4.86 (1H, sextet, J = 6 Hz, 172-COOCH), 4.45 (1H, dq, J = 2, 7 Hz, 18-H), 4.20 (1H, dt, J = 9, 2 Hz, 17-H), 3.63 (2H, q, J = 8 Hz, 8-CH2), 3.56 (3H, s, 12-CH3), 3.39 (3H, s, 2-CH3), 3.22 (3H, s, 7-CH3), 2.67–2.46 (2H, m, 171-CH2), 2.31–2.11 (2H, m, 17-CH2), 1.77 (3H, d, J = 7 Hz, 18-CH3), 1.66 (3H, t, J = 8 Hz, 81-CH3), 1.61–1.43 (2H, m, 172-COOCCH2), 1.16 (3H, d, J = 6 Hz, 172-COOCCH3), 0.85 (3H, t, J = 7 Hz, 172-COOC2CH3), 0.10, − 1.92 (each 1H, br-s, NH × 2) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 595.3271 calcd. for C36H43N4O4: MH+, 595.3279.

(R)-2-Octyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (3bR): Reduction of 4bR (129.8 mg) gave the titled alcohol (87.2 mg, 134 μmol, 67%): black solid; mp 101–102 °C; VIS (CH2Cl2) λmax/nm = 663 (relative intensity, 0.47), 605 (0.08), 557 (0.04), 536 (0.10), 505 (0.11), 470 (0.05), 410 (1.00), 397 (0.83), 377 (0.58), 319 (0.22); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.32 (1H, s, 5-H), 9.27 (1H, s, 10-H), 8.50 (1H, s, 20-H), 5.78 (2H, s, 3-CH2), 5.11, 5.00 (each 1H, d, J = 20 Hz, 131-CH2), 4.88 (1H, sextet, J = 7 Hz, 172-COOCH), 4.42 (1H, br-q, J = 7 Hz, 18-H), 4.17 (1H, br-d, J = 9 Hz, 17-H), 3.60 (2H, q, J = 7 Hz, 8-CH2), 3.51 (3H, s, 12-CH3), 3.36 (3H, s, 2-CH3), 3.19 (3H, s, 7-CH3), 2.61–2.45 (2H, m, 171-CH2), 2.26–2.09 (2H, m, 17-CH2), 1.75 (3H, d, J = 7 Hz, 18-CH3), 1.64 (3H, t, J = 7 Hz, 81-CH3), 1.53–1.44, 1.42–1.33 (each 1H, m, 172-COOCCH2), 1.25–1.13 (8H, m, 172-COOC2(CH2)4), 1.16 (3H, d, J = 7 Hz, 172-COOCCH3), 0.81 (3H, t, J = 7 Hz, 172-COOC6CH3), − 1.98 (each 1H, br-s, NH) [Another inner NH and the 31-OH signals were invisible.]; HRMS (APCI) found: m/z = 651.3879, calcd. for C40H51N4O4: MH+, 651.3905.

(S)-2-Octyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (3bS): Reduction of 4bS (129.8 mg) gave the titled alcohol (113.3 mg, 174 μmol, 87%): black solid; mp 101–102 °C; VIS (CH2Cl2) λmax/nm = 662 (relative intensity, 0.48), 605 (0.08), 558 (0.03), 536 (0.09), 505 (0.10), 472 (0.04), 411 (1.00), 397 (0.78), 377 (0.56), 318 (0.21); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.38 (1H, s, 5-H), 9.37 (1H, s, 10-H), 8.53 (1H, s, 20-H), 5.85 (2H, s, 3-CH2), 5.18, 5.03 (each 1H, d, J = 20 Hz, 131-CH2), 4.91 (1H, sextet, J = 6 Hz, 172-COOCH), 4.46 (1H, dq, J = 2, 7 Hz, 18-H), 4.20 (1H, dt, J = 9, 2 Hz, 17-H), 3.64 (2H, q, J = 8 Hz, 8-CH2), 3.57 (3H, s, 12-CH3), 3.39 (3H, s, 2-CH3), 3.22 (3H, s, 7-CH3), 2.67–2.58, 2.54–2.48 (each 1H, m, 171-CH2), 2.30–2.11 (2H, m, 17-CH2), 1.78 (3H, d, J = 7 Hz, 18-CH3), 1.66 (3H, t, J = 8 Hz, 81-CH3), 1.56–1.47, 1.46–1.37 (each 1H, m, 172-COOCCH2), 1.29–1.12 (8H, m, 172-COOC2(CH2)4), 1.15 (3H, d, J = 7 Hz, 172-COOCCH3), 0.82 (3H, t, J = 7 Hz, 172-COOC6CH3), 0.12, − 1.90 (each 1H, br-s, NH × 2) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 651.3880, calcd. for C40H51N4O4: MH+, 651.3905.

(R)-1-Phenylethyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (3cR): Reduction of 4cR (128.2 mg) gave the titled alcohol (124.7 mg, 194 μmol, 97%): black solid; mp 137–138 °C; VIS (CH2Cl2) λmax/nm = 663 (relative intensity, 0.48), 604 (0.08), 556 (0.03), 536 (0.09), 505 (0.10), 473 (0.04), 410 (1.00), 397 (0.80), 377 (0.56), 319 (0.21); 1H NMR (CDCl3, 600 MHz) δ/ppm = 9.44 (1H, s, 10-H), 9.41 (1H, s, 5-H), 8.53 (1H, s, 20-H), 7.29–7.21 (5H, m, 172-COOCC6H5), 5.89 (1H, q, J = 7 Hz, 172-COOCH), 5.88 (2H, s, 3-CH2), 5.15, 5.00 (each 1H, d, J = 19 Hz, 131-CH2), 4.45 (1H, dq, J = 2, 7 Hz, 18-H), 4.22 (1H, dt, J = 9, 2 Hz, 17-H), 3.67 (2H, q, J = 8 Hz, 8-CH2), 3.62 (3H, s, 12-CH3), 3.40 (3H, s, 2-CH3), 3.25 (3H, s, 7-CH3), 2.67–2.61, 2.59–2.54 (each 1H, m, 171-CH2), 2.29–2.17 (2H, m, 17-CH2), 2.18 (1H, br, 31-OH), 1.75 (3H, d, J = 7 Hz, 18-CH3), 1.68 (3H, t, J = 8 Hz, 81-CH3), 1.50 (3H, d, J = 7 Hz, 172-COOCCH3), 0.18, − 1.86 (each 1H, br-s, NH × 2); HRMS (APCI) found: m/z = 643.3265, calcd. for C40H43N4O4: MH+, 643.3279.

(S)-1-Phenylethyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (3cS): Reduction of 4cS (128.2 mg) gave the titled alcohol (124.7 mg, 194 μmol, 97%): black solid; mp 135–136 °C; VIS (CH2Cl2) λmax/nm = 663 (relative intensity, 0.48), 606 (0.08), 557 (0.03), 536 (0.09), 506 (0.10), 475 (0.04), 410 (1.00), 397 (0.80), 377 (0.56), 317 (0.20); 1H NMR (CDCl3, 400 MHz) δ/ppm = 9.37 (1H, s, 5-H), 9.36 (1H, s, 10-H), 8.49 (1H, s, 20-H), 7.28–7.22 (5H, m, 172-COOCC6H5), 5.87 (1H, q, J = 7 Hz, 172-COOCH), 5.84 (2H, s, 3-CH2), 5.13, 4.97 (each 1H, d, J = 20 Hz, 131-CH2), 4.39 (1H, dq, J = 2, 7 Hz, 18-H), 4.17 (1H, dt, J = 8, 2 Hz, 17-H), 3.64 (2H, q, J = 7 Hz, 8-CH2), 3.76 (3H, s, 12-CH3), 3.57 (3H, s, 2-CH3), 3.22 (3H, s, 7-CH3), 2.62–2.48 (2H, m, 171-CH2), 2.29–2.15 (2H, m, 17-CH2), 1.72 (3H, d, J = 7 Hz, 18-CH3), 1.67 (3H, t, J = 7 Hz, 81-CH3), 1.44 (3H, d, J = 7 Hz, 172-COOCCH3), 0.10, − 1.93 (each 1H, br-s, NH × 2) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 643.3263, calcd. for C40H43N4O4: MH+, 643.3279.

2.5 Synthesis of zinc 3-hydroxymethyl-pyropheophorbides-a 2aR/S–2cR/S

Free base 3 (180 μmol) was dissolved into dichloromethane (20 ml) in the dark under nitrogen at room temperature, to which a methanol solution saturated with zinc acetate dihydrate (10 ml) was added. After stirred for 30 min, the reaction mixture was diluted with dichloromethane (30 ml), washed with an aqueous solution saturated with sodium hydrogen carbonate and distilled water, dried over sodium sulfate, and filtered. All the solvents were evaporated to give the corresponding zinc complex 2.

Zinc (R)-2-butyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (2aR): Zinc metalation of 3aR (107.1 mg) gave the titled zinc complex (106.6 mg, 162 μmol, 90%): black solid; mp > 300 °C; VIS (THF) λmax/nm = 646 (relative intensity, 0.74), 602 (0.10), 566 (0.06), 521 (0.03), 490 (0.02), 424 (1.00), 404 (0.57), 381 (0.31), 315 (0.20); 1H NMR (CDCl3–10% pyridine-d5, 400 MHz) δ/ppm = 9.47 (1H, s, 10-H), 9.29 (1H, s, 5-H), 8.23 (1H, s, 20-H), 5.76 (2H, s, 3-CH2), 5.10, 4.96 (each 1H, d, J = 20 Hz, 131-CH2), 4.69 (1H, sextet, J = 6 Hz, 171-CH2), 4.31 (1H, dq, J = 2.5, 7.5 Hz, 18-H), 4.10 (1H, dt, J = 8, 2.5 Hz, 17-H), 3.64 (2H, q, J = 7.5 Hz, 8-CH2), 3.59 (3H, s, 12-CH3), 3.19 (3H, s, 2-CH3), 3.08 (3H, s, 7-CH3), 2.52–2.41, 2.32–2.22 (each 1H, m, 171-CH2), 2.21–2.09, 1.92–1.83 (each 1H, m, 17-CH2), 1.62 (3H, d, J = 7.5 Hz, 18-CH3), 1.59 (3H, t, J = 7.5 Hz, 81-CH3), 1.36 (2H, m, 172-COOCCH2), 1.02 (3H, d, J = 6 Hz, 172-COOCCH3), 0.70 (3H, t, J = 7 Hz, 172-COOC2CH3) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 657.2392, calcd. for C36H41N4O4Zn: MH+, 657.2414.

Zinc (S)-2-butyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (2aS): Zinc metalation of 3aS (107.1 mg) gave the titled zinc complex (109.0 mg, 166 μmol, 92%): black solid; mp 249–250 °C; VIS (THF) λmax/nm = 646 (relative intensity, 0.74), 602 (0.11), 566 (0.06), 521 (0.04), 489 (0.02), 424 (1.00), 404 (0.58). 382 (0.32), 315 (0.23); 1H NMR (CDCl3–10% pyridine-d5, 400 MHz) δ/ppm = 9.48 (1H, s, 10-H), 9.30 (1H, s, 5-H), 8.24 (1H, s, 20-H), 5.77 (2H, s, 3-CH2), 5.11, 4.97 (each 1H, d, J = 20 Hz, 131-CH2), 4.71 (1H, sextet, J = 6 Hz, 172-COOCH), 4.32 (1H, dq, J = 2, 7 Hz, 18-H), 4.11 (1H, dt, J = 8, 2 Hz, 17-H), 3.65 (2H, q, J = 8 Hz, 8-CH2), 3.61 (3H, s, 12-CH3), 3.21 (3H, s, 2-CH3), 3.09 (3H, s, 7-CH3), 2.53–2.42, 2.35–2.24 (each 1H, m, 171-CH2), 2.21–2.10, 1.93–1.83 (each 1H, m, 17-CH2), 1.63 (3H, d, J = 7 Hz, 18-CH3), 1.60 (3H, t, J = 8 Hz, 81-CH3), 1.39 (2H, m, 172-COOCCH2), 1.04 (3H, d, J = 6 Hz, 172-COOCCH3), 0.72 (3H, t, J = 7 Hz, 172-COOC2CH3) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 657.2389, calcd. for C36H41N4O4Zn: MH+, 657.2414.

Zinc (R)-2-octyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (2bR): Zinc metalation of 3bR (117.2 mg) gave the titled zinc complex (91.3 mg, 128 μmol, 71%): black solid; mp 232–233 °C; VIS (THF) λmax/nm = 646 (relative intensity, 0.73), 602 (0.11), 566 (0.06), 520 (0.04), 488 (0.03), 424 (1.00), 404 (0.57), 381 (0.33), 315 (0.26); 1H NMR (CDCl3–10% pyridine-d5, 600 MHz) δ/ppm = 9.57 (1H, s, 10-H), 9.39 (1H, s, 5-H), 8.33 (1H, s, 20-H), 5.88, 5.84 (each 1H, d, J = 12 Hz, 3-CH2), 5.20, 5.07 (each 1H, d, J = 19 Hz, 131-CH2), 4.85 (1H, sextet, J = 6 Hz, 172-COOCH), 4.41 (1H, br-q, J = 7 Hz, 18-H), 4.20 (1H, br-d, J = 8 Hz, 17-H), 3.74 (2H, q, J = 8 Hz, 8-CH2), 3.69 (3H, s, 12-CH3), 3.29 (3H, s, 2-CH3), 3.18 (3H, s, 7-CH3), 2.59–2.53, 2.29–2.22 (each 1H, m, 17-CH2), 2.39–2.33, 2.00–1.94 (each 1H, m, 171-CH2), 1.72 (3H, d, J = 7 Hz, 18-CH3), 1.69 (3H, t, J = 8 Hz, 81-CH3), 1.51–1.45, 1.40–1.34 (each 1H, m, 172-COOCCH2), 1.30–1.16 (8H, m, 172-COOC2(CH2)4), 1.13 (3H, d, J = 6 Hz, 172-COOCCH3), 0.83 (3H, t, J = 7 Hz, 172-COOC6CH3) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 713.3035, calcd. for C40H49N4O4Zn; MH+, 713.3040.

Zinc (S)-2-octyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (2bS): Zinc metalation of 3bS (117.2 mg) gave the titled zinc complex (91.3 mg, 128 μmol, 71%): black solid; mp 244–245 °C; VIS (THF) λmax/nm = 646 (relative intensity, 0.74), 602 (0.11), 566 (0.06), 521 (0.04), 487 (0.03), 424 (1.00), 404 (0.57), 380 (0.32), 315 (0.23); 1H NMR (CDCl3–10% pyridine-d5, 400 MHz) δ/ppm = 9.57 (1H, s, 10-H), 9.39 (1H, s, 5-H), 8.33 (1H, s, 20-H), 5.88, 5.84 (each 1H, d, J = 12 Hz, 3-CH2), 5.21, 5.06 (each 1H, d, J = 20 Hz, 131-CH2), 4.86 (1H, sextet, J = 6 Hz, 172-COOCH), 4.41 (1H, dq, J = 2, 7 Hz, 18-H), 4.20 (1H, dt, J = 8, 2 Hz, 17-H), 3.74 (2H, q, J = 8 Hz, 8-CH2), 3.69 (3H, s, 12-CH3), 3.29 (3H, s, 2-CH3), 3.17 (3H, s, 7-CH3), 2.62–2.51, 2.45–2.33 (each 1H, m, 171-CH2), 2.30–2.19, 2.03–1.91 (each 1H, m, 17-CH2), 1.72 (3H, d, J = 7 Hz, 18-CH3), 1.69 (3H, t, J = 8 Hz, 81-CH3), 1.55–1.45, 1.44–1.34 (each 1H, m, 172-COOCCH2), 1.29–1.15 (8H, m, 172-COOC2(CH2)4), 1.13 (3H, d, J = 6 Hz, 172-COOCCH3), 0.83 (3H, t, J = 7 Hz, 172-COOC6CH3) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 713.3052, calcd. for C40H49N4O4Zn; MH+, 713.3040.

Zinc (R)-1-phenylethyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (2cR): Zinc metalation of 3cR (115.7 mg) gave the titled zinc complex (123.4 mg, 175 μmol, 97%): black solid; mp > 300 °C; VIS (THF) λmax/nm = 646 (relative intensity, 0.75), 602 (0.10), 566 (0.05), 521 (0.03), 488 (0.01), 424 (1.00), 404 (0.57), 380 (0.31), 315 (0.22); 1H NMR (CDCl3–10% pyridine-d5, 600 MHz) δ/ppm = 9.56 (1H, s, 10-H), 9.38 (1H, s, 5-H), 8.31 (1H, s, 20-H), 7.30–7.21 (5H, m, 172-COOCC6H5), 5.85 (2H, s, 3-CH2), 5.83 (1H, q, J = 7 Hz, 172-COOCH), 5.16, 5.02 (each 1H, d, J = 19 Hz, 131-CH2), 4.37 (1H, dq, J = 2, 7 Hz, 18-H), 4.17 (1H, dt, J = 8, 3 Hz, 17-H), 3.74, 3.72 (each 1H, dq, J = 15, 8 Hz, 8-CH2), 3.69 (3H, s, 12-CH3), 3.29 (3H, s, 2-CH3), 3.17 (3H, s, 7-CH3), 2.58–2.52, 2.41–2.34 (each 1H, m, 171-CH2), 2.30–2.22, 1.95–1.89 (each 1H, m, 17-CH2), 1.69 (3H, d, J = 7 Hz, 18-CH3), 1.69 (3H, t, J = 8 Hz, 81-CH3), 1.46 (3H, d, J = 7 Hz, 172-COOCCH3) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 705.2400, calcd. for C40H41N4O4Zn: MH+, 705.2414.

Zinc (S)-1-phenylethyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (2cS): Zinc metalation of 3cS (115.7 mg) gave the titled zinc complex (123.3 mg, 175 μmol, 97%): black solid; mp 234–235 °C; VIS (THF) λmax/nm = 646 (relative intensity, 0.73), 602 (0.11), 566 (0.06), 521 (0.04), 487 (0.03), 424 (1.00), 404 (0.58), 381 (0.33), 315 (0.26); 1H NMR (CDCl3–10% pyridine-d5, 400 MHz) δ/ppm = 9.57 (1H, s, 10-H), 9.39 (1H, s, 5-H), 8.31 (1H, s, 20-H), 7.29–7.20 (5H, m, 172-COOCC6H5), 5.86 (2H, s, 3-CH2), 5.82 (1H, q, J = 7 Hz, 172-COOCH), 5.18, 5.09 (each 1H, d, J = 20 Hz, 131-CH2), 4.36 (1H, br-q, J = 7 Hz, 18-H), 4.17 (1H, dt, J = 8, 2 Hz, 17-H), 3.73 (2H, q, J = 7 Hz, 8-CH2), 3.70 (3H, s, 12-CH3), 3.29 (3H, s, 2-CH3), 3.17 (3H, s, 7-CH3), 2.57–2.50 (1H, m, 171-CH), 2.41–2.25 (2H, m, 17-CHCH), 1.96–1.88 (1H, m, 17-CH), 1.69 (3H, t, J = 7 Hz, 81-CH3), 1.68 (3H, d, J = 7 Hz, 18-CH3), 1.42 (3H, d, J = 7 Hz, 172-COOCCH3) [The 31-OH signal was invisible.]; HRMS (APCI) found: m/z = 705.2394, calcd. for C40H41N4O4Zn; MH+, 705.2413.

2.6 Synthesis of zinc 3-hydroxymethyl-pyroprotopheophorbides-a 1aR/S–1cR/S

Zinc chlorin 2 (100 μmol) was dissolved into pyridine (2 ml) in the dark under nitrogen at room temperature, to which an acetone solution (20 ml) of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ, 34.1 mg, 150 μmol) was added dropwise. After stirred for 10 min, the reaction mixture was diluted with chloroform (20 ml), washed with an aqueous 5% potassium hydrogen sulfate solution, an aqueous solution saturated with sodium hydrogen carbonate, brine, and distilled water, dried over sodium sulfate, and filtered. All the solvents were evaporated, and the residue was purified by HPLC with methanol and 5% pyridine to give the corresponding zinc porphyrin 1. The isolated yields were at most 45%. Since the products were less soluble in deuterated solvents, their well-resolved proton peaks could not be obtained in 1H NMR and the data are not shown below. Their purities were confirmed by HPLC (see Fig. S1).

Zinc (R)-2-butyl 3-devinyl-3-hydroxymethyl-pyroprotopheophorbide-a (1aR): Dehydrogenation of 2aR gave the titled zinc porphyrin: black solid; mp 280–281 °C; VIS (THF) λmax/nm = 609 (relative intensity, 0.11), 589 (0.04), 560 (0.06), 545 (0.04), 524 (0.03), 428 (1.00), 376 (0.13), 318 (0.13), 308 (0.12); HRMS (APCI) found: m/z = 655.2248, calcd. for C36H39N4O4Zn: MH+, 655.2257.

Zinc (S)-2-butyl 3-devinyl-3-hydroxymethyl-pyroprotopheophorbide-a (1aS): Dehydrogenation of 2aS gave the titled zinc complex: black solid; mp > 300 °C; VIS (THF) λmax/nm = 609 (relative intensity, 0.10), 589 (0.03), 560 (0.05), 545 (0.03), 524 (0.02), 428 (1.00), 376 (0.12), 320 (0.09), 308 (0.12); HRMS (APCI) found: m/z = 655.2239, calcd. for C36H39N4O4Zn: MH+, 655.2257.

Zinc (R)-2-octyl 3-devinyl-3-hydroxymethyl-pyroprotopheophorbide-a (1bR): Dehydrogenation of 2bR gave the titled zinc porphyrin: black solid; mp 257–258 °C; VIS (THF) λmax/nm = 609 (relative intensity, 0.11), 588 (0.03), 560 (0.05), 545 (0.03), 524 (0.02), 428 (1.00), 377 (0.12), 319(0.10), 309 (0.10); HRMS (APCI) found: m/z = 711.2866, calcd. for C40H47N4O4Zn: MH+, 711.2883.

Zinc (S)-2-octyl 3-devinyl-3-hydroxymethyl-pyroprotopheophorbide-a (1bS): Dehydrogenation of 2bS gave the titled zinc porphyrin: black solid; mp 254–255 °C; VIS (THF) λmax/nm = 609 (relative intensity, 0.11), 588 (0.04), 560 (0.06), 545 (0.04), 524 (0.03), 428 (1.00), 376 (0.13), 319(0.12), 309 (0.12); HRMS (APCI) found: m/z = 711.2860, calcd. for C40H47N4O4Zn: MH+, 711.2883.

Zinc (R)-1-phenylethyl 3-devinyl-3-hydroxymethyl-pyroprotopheophorbide-a (1cR): Dehydrogenation of 2cR gave the titled zinc porphyrin: black solid; mp > 300 °C; VIS (THF) λmax/nm = 609 (relative intensity, 0.11), 589 (0.03), 561 (0.05), 545 (0.03), 524 (0.02), 428 (1.00), 377 (0.12), 321(0.10), 307 (0.10); HRMS (APCI) found: m/z = 703.2254, calcd. for C40H39N4O4Zn: MH+, 703.2257.

Zinc (S)-1-phenylethyl 3-devinyl-3-hydroxymethyl-pyroprotopheophorbide-a (1cS): Dehydrogenation of 2cS gave the titled zinc porphyrin: black solid; mp > 300 °C; VIS (THF) λmax/nm = 609 (relative intensity, 0.10), 589 (0.03), 560 (0.05), 545 (0.03), 524 (0.02), 428 (1.00), 377 (0.11), 321(0.09), 309 (0.08); HRMS (APCI) found: m/z = 703.2237, calcd. for C40H39N4O4Zn: MH+, 703.2257.