Antirhine synthesis

This suite of BVMOs is available via whole-cell expression systems and represents a complementary platform of biocatalysts for diverse applications in chiral synthesis. Representatives of this collection were utilized in the enantiodivergent synthesis of the indole alkaloids alloyohimbane and antirhine from a fused bicyclic precursor (Scheme 9.19) [151]. 

The first synthesis of ( )-antirhine (11) has been published by Takano and co-... 

Takano s group reported the first enantioselective total synthesis of (—)-anti-rhine as well (146). Chiral product 235 was prepared via a number of stereoselective reactions. Reductive condensation of 235 with tryptamine, using sodium cyanoborohydride at pH 6, supplied lactam 236, which was reduced by di-isobutylalminum hydride to hemiacetal 237. The latter could be cyclized to (-)-antirhine by simple acid treatment (146). 

After completing the enantioselective total synthesis of (+)-18,19-dihydro-antirhine [(+)-14](i40), Kametani et al. reported (394) the synthesis of (—)-antirhine [(-)-ll] by using (3S)-[3-hydroxy-( )-prop-l-enyl]cyclopentanone as a chiral synthon. 

An application of the ynamine cycloaddition is found in a synthesis of dihydro-antirhine [167]. The transition state with matching polarized addends is adopted. The cycloadduct becomes fragmentable upon hydrolysis. 

Pictet-Spengler isoquinoline synthesis. The final steps in a synthesis of (—)-antirhine (2), a Corynanthe-type indole alkaloid, involved partial reduction of the lactam 1 to a hemiamina), which cyclizes to 2 in the presence of dilute HC1,2... 

A retrosynthetic synthesis of (—)antirhine (Fig. 11) was performed through the monoacetate (1) and lactone (2) which was condensed with tryptamine. Product 3 was then finally converted, through a number of intermediates, to the tetracyclic (—)-antirhine, resulting in a remarkable overall yield of 13% (starting from the monoacetate 1), together with the 3-epimer (+)-antirhine at a yield of 6%. This strategy allowed the chemo-enzymatic synthesis of both (—) - and (+)-antirhines [82]. 

Fig. 11 Complete synthesis of the major alkaloid (—)-antirhine known from the plant Antirhea putaminosa (except for formation of 1, all other reaction steps were not enzyme-catalysed)...

Takano et al. have reported the first synthesis of ( )-antirhine (71) (Scheme 11),51 in which the problem of generating the desired, less stable (anti) stereochemistry at C-3 and C-15 was overcome by preparing the non-tryptamine fragment (72) from ( )-trinorcamphor (73) via a sequence of stereospecific reactions. Condensation of (72) with tryptamine, followed by cyclization and... 

The asymmetric synthesis of 6-lactone 8, a key intermediate for (-)-antirhine (a Corynanthe-type indole alkaloid)998 from optically pure alcohol 5a (>99% Z) involves such a type of Cope rearrangement969. The anionic oxy-Cope rearrangement of 6a under the standard conditions yields the erythro-yxoduct 7a with 80% de and 84% ee. 

Antirhine (1) is the major alkaloid of Antirhea jutaminosa, having a tra 5-3a-H,15 3-H structure with a cis CfD ring junction. A synthesis of 1 has been achieved starting with... 

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