Studies on vitamin D and related compounds XI investigations on sterols XIII the photoisomerisation of ergosterol

Abstract

Kinetic experiments on the photoisomerisation of ergosterol were carried out using different sources of light. New methods of analysis for pre‐ergocalciferol and tachysterol2 had to be developed. The quantum yield of the photoisomerisation of ergosterol with ultraviolet light of 2537 Å was found to be 0.31 at 20°. This value was obtained when ether, ethanol and petroleum ether were used as solvents. Tachysterol2 is not formed from ergosterol during irradiation, but originates exclusively from pre‐ergocalciferol. Excited ergosterol falls back to its ground state (69%) or transforms to pre‐ergocalciferol (26%) and to unidentified products (5%).

Continuous-flow synthesis of activated vitamin D3 and its analogues

“…The undesired products lumisterol (5) and tachysterol (6) result from the equilibrium between the products. 8,13 Therefore, with the present industrial method, it is necessary to interrupt the irradiation after a relatively low conversion (10 to 20%) of provitamin D 3 (3) to previtamin D 3 (4). The unconverted provitamin D 3 (3) is recycled while the previtamin D 3 (4) must be purified using a tedious work-up procedure.…”

Photochemistry Meets Natural‐Product Synthesis

“…After application of 350-nm light, a secondary mixture of 1 (8%), 2 (10%), 5 (73%), and 6 (9%) was found. If no other chemical change takes place, a photostationary mixture 15 ) is obtained, its composition (of 1, 2, 5, and 6) is determined by the absorptions of the participant molecules and the quantum yields of the reactions taking place (Scheme 6). After equilibration in boiling EtOH, a tertiary mixture of 5 and 7 in a 83:17 ratio was obtained, from which 50% vitamin D (7) could be isolated by MPLC (see Table 1,c).…”

“…Ring opening of (S)-2-methyloxirane (C* 3 building block in Scheme 41), accessible from (S)-lactic acid [105]) by the Grignard compound of the C 15 phenol derivative leads to the hydroxyalkyl-substituted phenol of Scheme 40.…”

Microflow Technology: Another Solution for the Site-Selective Modification of Multifunctionalized Molecules

“…10,12 However, the overall yields of the vitamin D 3 analogues obtained using photo and thermal reactions are generally low (<20%) 13 due to the poor selectivity of the photoisomerization step, and the tedious workup procedure that is required to isolate the labile intermediate previtamin D 3 . 12,14 We have developed a two-stage, microflow synthesis of vitamin D 3 using a high-intensity and economical light source, that is, a high-pressure mercury lamp (Figure 2). 9a The 30 mM solution of provitamin D 3 in 1,4-dioxane was introduced via a syringe pump at a flow rate of 5 μL min -1 .…”