Kasimir K. Pivnitsky

The role of germinal vesicle in maturation of Pleurodeles waltlii oocytes induced by steroids

The maturation of oocytes from unstimulated Pleurodeles waltlii females can be induced in vitro. All full-grown oocytes covered by follicular envelopes mature under the influence of progesterone, testosterone, and a synthetic steroid (CDMT). Enucleation of oocytes prior to maturation induction resulted in a significantly lower percentage of maturation. Irradiation, or the treatment of oocytes with actinomycin D, did not affect their maturation. Therefore the lower percentage of maturation after enucleation must be due to the lack of karyoplasm. Karyoplasm appears to be necessary for the production of the maturation-promoting factor in P. waltlii oocytes.

Investigation of the diastereofacial selectivity of the addition of 1-metalated (E)- and (Z)-hept-1-enes to the COREY aldehyde — A comparison between vinyllithium and vinyltitanium compounds1,2

Abstract In connection with the synthesis of prostaglandin intermediates a comparison of the addition of ( Z )- and ( E )-hept-1-enyllithium and ( Z )- and ( E )-hept-1-enyltitanium triisopropoxide to the COREY aldehyde revealed that the lithium compounds are preferentially added by a si -attack, the titanium compounds, however, by a preferred re -attack. The diastereoselectivity of the lithium compounds was generally better than that of the titanium analogues. This result is explained by assuming a different chelation tendency of the metals. Molecular mechanics calculations support this interpretation.

Reversilbility of titanocene-catalyzed hydromagnesation of silylacetylenes

Abstract The regioisomeric silylvinylmagnesium compounds A and B , products of titanocene-catalyzed hydromagnesation of the trimethylsilylacetylenes, are in a rapid dynamic equilibrium with starting acetylene and, therefore, with each other due to the reversibility of the reaction. The existence of this equilibrium is demonstrated by transfer, under the conditions of hydromagnesation, of HMgBr from the vinylmagnesium compounds A / B to other acetylenes with regeneration of the starting acetylenes. Me 3 Si(BrMg)Cue5fbC(H)R ( A )⇋Me 3 SiCue5fcCR⇋Me 3 Si(H)Cue5fbC(MgBr) ( B . The position of the equilibrium between A and B was determined by deuterolysis and found to depend on the substituent, being 77 : 23 for R = n-C 5 H 11 and 95 : 5 for R = cyclo -CH 2 C 6 H 11 in diethyl ether. Reactions of the magnesium reagents A / B with electrophiles produce mixtures of linear (type A ) and branched (type B ) products. The ratios of regioisomeric products differ depending on the electrophile and the conditions (from 98 : 2 to 20 : 80). This is due to the preferential reaction of one of the regioisomers and to rapid equilibriation.

Enzymes in organic synthesis. Part 3. Synthesis of enantiomerically pure prostaglandin intermediates by enzyme-catalyzed transesterification of (1SR,2RS,5SR,6RS)-bicyclo[3.3.0]octane-2,6-diol with trichloroethyl acetate in an organic solvent

Since the pancreatin-catalyzed esterification of the diol (1) with 2,2,2-trichloroethyl acetate in tetrahydrofuran is significantly slower than the esterification of the enantiomer ent-(1), the diacetate ent-(3) can be obtained from the racemic diol rac-(1) in a chemical yield of 30–35% and an enantiomeric excess (e.e.) of 97– > 99%. When the remaining enantiomerically enriched diol (1) with an e.e. in the order of 55–68% was subjected once more to the pancreatin-catalyzed esterification its e.e. could be enhanced to 90%. Then acetylation and recrystallization afforded the diacetate (3) in a chemical overall yield of 37% and an e.e. of > 99%.