1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

6.2.2 Semi-Natural Cycloketo-Porphyrin Systems
6.2.2.1 Methyl Pyropheophorbide a, Me-33, from Spirulina Platensis
N
NH HN
N
Me-33
O
C 34 H 36 N 4 O 3
M = 548.67 g·mol -1
O
O
Experimental Section 6
In a 500 mL beaker, 100 g of dry spirulina platensis are
suspended in 300 mL of water and allowed to soak for 3 h. The
obtained algal pulp is then homogenized with a commercial hand
blender and slowly poured into liquid nitrogen furnishing small
pellets. Those are transferred into a 2 L round bottom flask,
which is then filled with acetone. This reaction mixture is stirred
at rt for 20 h. Upon filtration, the separated cellular material is
washed with acetone and the combined washings are
evaporated to dryness to give an oily dark brown residue. To
isolate pheophytin a 31, that material is subjected to FC on silica whereat the polarity of the
eluent is risen stepwise: 1 st hexanes, 2 nd hexanes : CH2Cl2 (1 : 1), 3 rd CH2Cl2, 4 th CH2Cl2 : ethyl
acetate (9 : 1). Finally, 31 elutes in black purple color. That solution is then evaporated to
dryness before a N2 saturated methanolic solution of H2SO4 (100 mL, 5 wt% H2SO4) is added.
After stirring at rt for 15 h under N2, the reaction mixture is concentrated and washed with
water, a saturated aqueous solution of NaHCO3 and water, dried over Na2SO4 and again
evaporated to dryness. In a 250 mL round bottom flask, the thus obtained methyl
pheophorbide a 32 is dissolved in 100 mL of 2,4,6-collidine and degassed with N2 for 20 min
before the reaction mixture is refluxed for 5 h (∼ 180 °C). Subsequently, the solvent is
removed by vacuum distillation and the crude product is washed with 6 M aqueous HCl,
water, a saturated aqueous solution of NaHCO3 and water and finally dried over Na2SO4.
Purification is finally accomplished by FC (silica, CH2Cl2 : ethyl acetate = 9 : 1) to give 600-
800 mg pure methyl pyropheophorbide a Me-33 as dark purple powder.
1 H NMR (400 MHz, rt, CDCl3): δ [ppm] = -1.77 (s, 1 H, NH), 0.37 (s, 1 H, NH), 1.64 (t,
3 J = 7.6 Hz, 3 H, 8 2 ), 1.80 (d, 3 J = 7.2 Hz, 3 H, 18 1 ), 2.27, 2.55, 2.68 (3m, 2+1+1 H, 17 1 & 17 2 ),
3.16 (s, 3 H, 7 1 ), 3.37 (s, 3 H, 2 1 ), 3.60 (s, 3 H, 17 4 & q, 3 J = 7.6 Hz, 2 H, 8 1 ), 3.61 (s, 3 H, 12 1 ),
4.27 (m, 1 H, 17), 4.46 (m, 1 H, 18), 5.09, 5.24 (2d, 2 J = 19.6 Hz, 1+1 H, 13 2 ), 6.13 (dd,
2 J = 1.6 Hz, 3 J = 11.6 Hz, 1 H, 3 2 cis), 6.24 (dd, 2 J = 1.6 Hz, 3 J = 17.6 Hz, 1 H, 3 2 trans), 7.94 (dd,
3 J = 11.6 Hz, 3 J = 17.6 Hz, 1 H, 3 1 ), 8.52 (s, 1 H, 20), 9.29 (s, 1 H, 5), 9.40 (s, 1 H, 10).
141