Morphinans synthesis

Belleau and a Bristol Laboratories group developed a novel morphinan synthesis which leads to 14-hydroxy derivatives.(62) The procedure rests upon rearrangement of the spirane 13 and may be adapted to provide either 14-/3-or 14-a-hydroxy (iso) diastereoisomers (see 13 and p. 110). Out of this work... 

Dibenz[h,e]azepine-6,11-diones ent-Morphinan nomenclature, 1, 29 Morphinan, 1,2,3,4-tetrahydro-nomenclature, 1, 29 14-a-Morphinan, N-methyl-synthesis, 1, 480 Morphinans nomenclature, 1, 29 as pharmaceuticals, 1, 148 synthesis, 2, 377 Morphine, 2, 512 as analgesic, 1, 167 as metabolite of normorphine, 1, 235 as pharmaceutical, 1, 146, 147, 148 synthesis, 1, 480 Morphine alkaloids structure, 4, 534 Morphin-7-en nomenclature, 1, 29 Morphinone, dihydro-as pharmaceutical, 1, 147 Morpholine — see also 1,4-Oxazine, tetrahydrocarcinogenicity, 1, 229 corrosion inhibitor, 1, 409 metabolism, 1, 226 nomenclature, 3, 996 structure, 2, 5 synthesis, 2, 89 Morpholine, 4-aciyloyl-polymers, 1, 291 Morpholine, alkenyl-polymers, 1, 291... 

Hong, C.Y, Kado, N., Overman, L.E. (1993) Asymmetric Synthesis of Either Enantiomer of Opium Alkaloids and Morphinans. Total Synthesis of (—)- and (-f)-Dihydrocodeinone and (—)- and (-F)-Morphine. Journal of the American Chemical Society, 115, 11028-11029. 

The Diels-Alder reaction of morphinan-6,8-dienes with nitroethene affords a novel type of opium alkaloids (Eq. 8.3).10a High reactivity of nitroethylene is demonstrated for the Diels-Alder reaction with thermally unstable dienes, and this is used for synthesis of polycyclic kopsane-like alkaloids.1013... 

Somewhat more effective catalysts are obtained by replacing BINAP with TolBINAP, which is 2,2 -bis(di-p-tolylphosphino)-l,l -binaphthyl.4 The presently preferred catalysts are complexes of Ru(OCOCF3)2 with (R)- or (S)-TolBINAP, obtained by treatment of Ru(OAc)2TolBINAP with 2 equiv. of trifluoroacetic acid. Such catalysts promote hydrogenation of typical enamides in 98% ee and 98% yield. This reaction can be used to provide asymmetric synthesis of isoquinoline alkaloids as well as of morphinans used as substitutes for morphine. 

Morphine (10) and codeine (11), constituents of opium, are the most interesting alkaloids found in nature. Morphine is also the oldest alkaloid isolated, in 1805, by the German pharmacist Sertiimer from opium, the sun dried latex of Papaver somniferum. The structure of morphine with its so-called morphinan skeleton, once called the acrobat under the alkaloids, was finally elucidated in 1952 by the first total synthesis performed by Gates and Tschudi. Many syntheses would follow [26], but all morphine used today, whether legal or illicit, originates in the natural source P. somniferum or its extract, opium. The latex may contain up to 20% morphine. Most legal morphine is converted into the anticough medicine codeine (Table 5.1) by treatment with trimethylanilinium methoxide, whereas almost all illicit morphine is acetylated to the diacetate heroin. 

The Delft synthesis makes use of an acid-catalyzed ring closure - in fact an intramolecular aromatic alkylation - of a l-(3,5-dihydroxy-4-methoxybenzyl) isoquinoline derivative that is prepared starting from (natural) gallic acid. One of the hydroxyl groups is removed via a Pd/ C hydrogenation of the benzyl ether. Other catalytic steps play an important role some steps were improved recently [27]. The crucial step in the Rice synthesis makes use of a l-(2-bromo-5-hydroxy-4-methoxybenzyl)isoquinoline derivative that is also cyclized in an acid-catalyzed ring closure to the morphinan skeleton, followed by catalytic removal of the bromo substituent (Scheme 5.8). 

For the synthesis of Diels-Alder adducts a morphinan-6,8-diene system, as present in thebaine, is indispensable. Older publications started from thebaine and methyl vinyl ketone (but-3-en-2-one), yielding, after a Grignard reaction with propylmagnesium bromide, etorphine (13), a 6,14-endoethenomorphinan that is over 1000x as active as morphine and is used in veterinary medicine (Scheme 5.10). 

Morphinans came about from early attempts at the total synthesis of morphine by a german chemist named R. Grew. Containing the complete carbon-nitrogen skeleton of morphine they are the closest chemical relatives which have been obtained by total synthesis. 

Gawley and coworkers showed that oxazolines can be used in place of formamidines for asymmetric alkylations of tetrahydroisoquinolines. A number of substituted oxazolines were evaluated as chiral auxiliaries, and one derived from valinol was found to be optimal. Interestingly, the same enantiomer of valinol affords the opposite enantiomers of the substituted tetrahydroisoquinoline when incorporated into formamidine or oxazoline auxiliaries. An example is shown in Scheme 58, as applied to a synthesis of laudanosine and the morphinan 9-7 -0-methylflavinantine. ° ... 

The addition of acid to Az-piperideine results in an iminium ion that readily reacts with nucleophilic species. This reaction has been particularly useful for the formation of carbon-carbon bonds in alkaloid total synthesis. For example, key steps in the total synthesis of ( )-porantherine (equation 36) (74JA6517), coccinelidine (equation 37) (77H(7)685) and eburnamonine (equation 38) (65JA1580) were acid-catalyzed ring closures between A2-piperideine derivatives and ends. Even the weakly nucleophilic carbon-carbon double bond can participate in this type of reaction (80JA5955), as has been demonstrated by a recent total synthesis of a morphinan derivative (Scheme 13). 

Hydroxylation at the equivalent of the 14 position in morphine has much the same effect in the morphinan series in that it increases both potency and oral activity. The somewhat involved synthesis of such a compound begins with the... 

SCHEME 24. General synthesis of moiphine, benzomorphans, and morphinans. 

A total of more than 20 total syntheses have been described which aim to generate the most important members of the morphinan-type alkaloids, morphine and codeine. These long-standing efforts in alkaloid synthesis have been primarily due to the exceptional pharmacological importance of both compounds, as the most efficacious therapies for pain and cough, respectively. 

Fig. 20 Fourteen-step synthesis of the complete morphinan skeleton of morphine and codeine, starting with the enzymatically formed diol providing ring C of the carbon frame work of these alkaloids [129, 130]...

In the morphinan series, the preparation of 3-alkyl-morphinans222 and 3-mercapto-morphinans223 has been described. In the benzomorphan series, a novel cleavage of aryl benzyl ethers and of aryl allyl ethers has been described and used in an improved synthesis of pentazocine. The lactam (162), on hydrogenolysis, gives the benzomorphan (163 R1 = R2 = H). Treatment of this with dimethylallyl... 

Morphinans (compactly fused Phe, C6, C5N, C6 and C40 rings) Codeine (opium-derived addictive, analgesic, antitussive, spasmolytic narcotic) morphine (opium-derived addictive, analgesic, antitussive, sedative, spasmolytic narcotic heroin is the semisynthetic diacetate) thebaine (non-analgesic, toxic, convulsant narcotic and semi-synthesis precursor of the anti-addiction drug naltrexone). 

---