Maria Valpuesta

Reaction of monosaccharaide derivatives with stabilized sulfur ylides. A highly stereoselective synthesis for C-glycofuranosides

Abstract Stereoselectivity in the formation of glycidic amides by reaction of various aldehydro- and ketosugars [ (1) , (4) , (6) , (8) , (10) and (12) ] with N,N-dimethyl-2-(dimethylsulfuranylidene)acetamide (2) was studied. The reaction with derivatives of reducing cyclohemiacetalic monosaccharides (14) and (21) , gives to α-C-glycofuranosyl-2(S)-hydroxyacetamides with a higher yield and stereoselectivity.

Structure and total synthesis of (-)-malacitanine. An unusual protoberberine alkaloid from ceratocapnos heterocarpa

Abstract The examination of the alkaloids present in Ceratocapnos heterocarpa (Papaveraceae) had led to the isolation of the new protoberberine alkaloid, (-)-malacitanine. Characteristic structural features for this alkaloid are the 1,2,10,11-substitution pattern and the hydroxymethyl group at C-8. The synthesis of (±)-malacitanine and its C-8 epimer from the benzylisoquinoline (±)-norcrassifoline has been developed. Spectroscopic data (pmr, cmr and ir) for several C-8 substituted protoberberine alkaloids are reported in connexion with the quinolizidine conformation.

Syntheses of dopaminergic 1-cyclohexylmethyl-7,8-dioxygenated tetrahydroisoquinolines by selective heterogeneous tandem hydrogenation

Abstract We describe the preparation in a ‘one-pot’ sequence 1-cyclohexylmethyl 7,8-dioxygenated tetrahydroisoquinoline, substituted and unsubstituted in the C ring by application of the Photo–Fries transposition, followed by a tandem reduction–cyclization and further reduction. Indeed, we have accomplished for the first time regioselective hydrogenation of the benzylic ring of the tetrahydroisoquinoline systems. All 1-cyclohexylmethyl THIQ synthesized were able to displace D2 dopamine receptor from its specific binding site in rat striatal membranes, while the N-methylated derivatives showed also affinity for D1 dopamine receptors.

The photo-fries rearrangement of 2,5-disubstituted phenyl acetates

Abstract In a homogeneous solution, the photo-Fries rearrangement of 2,5-disubstituted phenyl acetates gives ortho -hydroxyacetophenones as major photoproducts. The ortholpara ratio can be increased by using a highly viscous medium or restricted spaces such as those in zeolites. On the other hand, micellar solutions have little effect.

(-)-CASEAMINE FROM CERATOCAPNOS HETEROCARPA: STRUCTURE AND TOTAL SYNTHESIS

Abstract (−)-Caseamine was the major alkaloid isolated from Ceratocapnos heterocarpa. Its structure was elucidated by spectroscopic methods and by total s

From protopines to berbines: synthesis of 1-methoxystylopine and its N-metho salts from coulteropine

Abstract The transformation of protopines into berbines under improved conditions has been used to synthesize 1-methoxystylopine. Coulteropine, the main alkaloid from Romneya coulteri, was used as the starting protopine to accomplish the stereocontrolled synthesis of both cis and trans N-methyl-1-methoxystylopinium salts. The results of ab initio calculations (B3LYP/6-31G∗∗) which are consistent with experimental data, sustain the influence of the C-1 substituent on both the conformational equilibrium of berbines and the rate of N-methylation.

A novel oxidation stage in the chemistry of protoberberine alkaloids. Synthesis of 7,8-dehydroberbines

Abstract 1,2-substituted berbines, such as (–)-caseamine, (–)-caseadine and (–)-O-methylcaseadine, are partially oxidized by iodine to the 7,8-dehydroberbines, while the 2,3-substituted berbines are oxidized all the way to the protoberberinium salts. This different behaviour is interpreted in terms of the preferred cis or trans B/C quinolizidine conformation of the starting berbines.

Cularine alkaloids from Ceratocapnos heterocarpa

Abstract The new cularine alkaloid (+)-norsarcocapnine has been isolated from Ceratocapnos heterocarpa, together with (+)-cularidine, oxocompostelline and oxosarcocapnine.

(±)-heterocarpine, a hydroxymethylated isoquinoline alkaloid from ceratocapnos heterocarpa

Abstract Heterocarpine, a novel alkaloid from Ceratocapnos heterocarpa , has been characterised as (±)-1-hydroxymethyl-2-(3-hydroxy-4-methoxybenzyl)-7-hydroxy-6-methoxy-1,2,3,4-tetrahydroisoquinoline. The alkaloid was synthesized from the corresponding 3,4-dihydro isoquinoliniun salt. A key step in the process is the acid resin catalysed methanolysis of the 1-carbamoyl isoquinoline. The structural correlation of the hydroxymethylated alkaloids heterocarpine and malacitanine with their unsubstituted counterparts capnosine and caseamine, also present in the plant, might be of biosynthetic significance.

PHOTOCHEMICAL SYNTHESIS OF 7,8-DIOXYGENATED ISOQUINOLINE ALKALOIDS

Abstract A new approach to the synthesis of 7,8-dioxygenated tetrahydroisoquinoline alkaloids based on the phot-Fries rearrangement of esters derived from 3-hydroxy-4-methoxy phenylacetonitrile is reported. The procedure was applied to the synthesis of the alkaloid Arizonine and 1-benzyl tetrahydroisoquinoline precursor of cularine and 1,2-berbine alkaloids.