Synthesis of tritium labelled 24‐epibrassinolide

Abstract

SUMMARYDeuterium and tritium 5,7,7-tris-labelled 24-epibrassinolide were prepared by base catalyzed exchange reaction using 24-epicastasterone tetraacetate I or bis-isopropylidenedioxy-24-epicastasterone 8 and labelled water. Baeyer-Villiger oxidation of the obtained labelled 6-ketones 2 and 3 with CF3C03H gave after alkaline deacetylation of the resulting 4 and 5 the desired tris-labelled 24-epibrassinolides 6 and 2, respectively, or starting from 9 under simultaneous oxidation and deprotection in one step the same final products.

A facile method for steroid labeling by heavy isotopes of hydrogen

“…After the completion of the reaction (monitored by TLC; SiO 2 ; CHCl 3 /MeOH, 10:1), the suspension was neutralized by 1M aqueous HCl and the product was extracted into DCM (3Â5 mL). The combined organic layers were dried by anhydrous MgSO 4 (3 mL) at 0 C. The reaction mixture was stirred for 30 min at 0 C and then the cooling bath was removed and the reaction mixture was left to warm up to room temperature. After additional 4 h, the reaction mixture was diluted by CHCl 3 (10 mL) and then washed successively with a saturated aqueous solution of NaHCO 3 (5 mL) and water (5 mL).…”

“…Studies on the mechanism of action of biologically active compounds on the molecular level require the labeling of these substances by the radionuclide 3 H. Only one example of such synthesis has been published. 4 However, 24- [5, H]epibrassinolide, prepared by a base-catalyzed exchange with tritiated water, had very low specific activity (6.3 mCi/mmol); moreover, the product was labeled on the exchangeable position. A general method providing [ 3 H]-labeled BRs in high specific activity is seriously missing.…”

Recent Developments in a Radio-labeling of Brassinosteroids

“…Tritium-labeled protected 24-epiCS and 24-epiBL [ 3 H]-1 were for the first time prepared by Kolbe et al [23]. By very simple procedure of base-catalyzed exchange reaction with tritiated water (SA = 20.10 −3 Ci/mmol-accounts for 0.7 × 10 −3 tritium atom per molecule HTO) to the enolizable alpha positions of C-6 ketone of tetracetate 24-epiCS 27 (Figure 11).…”

Enantiospecific tritium labeling of 28-homocastasterone

“…This led to low radiochemical yields of 3.2% and 4.5%, respectively, of synthesized (22 R ,23 R )‐ and (22 S ,23 S )‐24‐[4‐ 14 C]epibrassinolide. Kolbe et al have published 2 papers dealing with the introduction of an alternative isotope—tritium—into the enolizable positions of a BR skeleton via a based‐catalyzed exchange with tritiated water . However, this method has provided only low specific activities (SAs) (about 6.10 ‐3 Ci/mmol) of labeled BRs; moreover, the label placed in exchangeable positions will most probably be unstable under physiological conditions.…”