Science of Synthesis

Clapés, P.; Fessner, W. -D., Science of Synthesis: Stereoselective Synthesis, (2011) 2, 729.

d-Fructose 6-phosphate aldolase from E. coli (FSA, described in Section ‌2.14.2‌) can also utilize 2-hydroxyacetaldehyde (glycolaldehyde; GA) as a nucleophilic aldol component and thus can catalyze a direct self-aldolization to furnish d-(−)-threose (‌Scheme 40‌). In the presence of other aldehydes, 2-hydroxyacetaldehyde invariably acts as a donor for the corresponding cross-aldol additions. In the competition between self addition and cross addition of 2-hydroxyacetaldehyde, the extent of the desired cross-aldol reaction depends on the substrate quality of the acceptor aldehyde, but can be further increased by maintaining a low 2-hydroxyacetaldehyde concentration in the reaction medium, e.g. by slow addition of this compound with the aid of a syringe pump.[‌172‌] Formation of cross-aldol adducts is also favored by the formation of stable cyclic hemiacetals or hemiaminals as occurs with the examples ‌86‌ shown in ‌Scheme 40‌. The exemplary reactions show high stereoselectivity (>99%) for (2S)-configured syn-adducts. As with other enzymatic aldol additions these reactions are conveniently carried out at ambient conditions in water, or with up to 20% of dimethylformamide as cosolvent to enhance the solubility of hydrophobic aldehydes.

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8-[(Meeeeeeeeeeeeeeee)eeeee]eeeeeeee (888 ee, 8.8 eeee) eee eeeeeeeee ee MMM (8 eM) eee e 8.888 M eeeeeeeeeeeeeee eeeeee eeee (88 eM, eM 8.8) eee eeeee. Me eee eeeee eeeeeee eeee eeeeeeee, MMM eeeeee (88 ee, 8.88 M · ee−8 eeeeee) eee eeeee, eee eee eeeeeeeee eeeeeee eee eeeeee ee ee eeeeeee eeeeee (888 eee) ee 88 °M. M eeee ee 8-eeeeeeeeeeeeeeeeeee (888 ee, 8.8 eeee) ee M8M/MMM (8:8; 88 eM) eee eeeee eeeeee 88 e eeeeeeeee e eeeeeee eeee. Meeeeeeeee eeeeee (88 ee) eee eeeee eeeee 88 e ee eeeeeeee. Meeeeeeee ee e-(−)-eeeeeee, eeeeeee ‌88‌, eee eee eeee 8-eeeeeeeeeeeeeeeeeee ee eeee eeee eeeeeeeee eee 88 e ee MMMM eeeeeeee ee eeeee eee eeeeeeeeeee eeeeeee (eee eeeee) eee eeeeeeeee eee eeeeeeee eeee ee 8-eeeeeeeeeeeeeeeeeee eee eeeeeeee ee eeeee eee eeeeeeeeeeee ee eee eeeeeee. Meeee 88 e, eee eeeeeee eee eeeeee eeee e eeeeeeeeeeeeee eeeeee (88 × 888 ee) eeeeee eeee Meeeeeeee MMM88 eee eeeeeeeeeeee eeee eeeee M8M. Mee eeeeeee eee eeeeeeee eee eeeeee eeee eeeee M8M (8 eeeeee eeeeeee) ee eeeeeeeee eee eeeeee ee eeeeeeee eee eeeeee. Meeeeee, eee eeeeeee eee eeeeee eeee MeMM/M8M (8:8) eee eee MeMM eee eeeeeee eeeee eeeeeee eeeeeeee. Mee eeeee eeeeeee eee eeeeee eeee e eeeeeeeeeeeeeee eeeeee MMeeee (88 × 888 ee). Meeeeeee eeee eeeeee eeeee MeMM eeeeeeee eeee 8 ee 88% MeMM ee 88 eee. Mee eeee eeee eee 88 eM · eee−8 eee eee eeeeeeee eeee eeeeeeee ee 888 ee. Meeeeeee ee eee eeeeeeeee eee eeeeeeeeeeee eeeee eeeeeeee eeeeeeeeee (88 ee 88% ee eeeeeee M ee 88 eee) ee eee eeeeeeeeee MMMM. Meee eeeeeeeee eeee eeeeee eee eeeeeeeeeee ee eeee eee eeeeeee, eeeee eee eeeeeeeeeeeee ee e eeeeeee ee eee eeeeeeeeee; eeeee: 888 ee (88%). Meeeee eeeeeeeeeeeeee: eeeeeeee eeeeeee (88 µM) eeee eeeee eeee e eeee ee M-eeeeeeeeeeeeeeeeeee eeeeeeeeeeeee (88 µM, 88.8 ee · eM−8; 8.88 eeee · eM−8 ee eeeeeeee/MeMM/M8M 88:88:8). Meeee eeeeeeeeee ee 88 °M eee 88 eee, eeeeeee eeee eeeeeee ee MeMM (888 µM) eee eeeeeeee eeeeeeee ee MMMM eeeeeeeeeeeeee.

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 88/8, 888.