The Conversion of Amines to Hydroxylamines

Europaisches Patentamt ® European Patent Office Office europeen des brevets (fi) Publication number : 0 450 823 A2 .12) EUROPEAN PATENT APPLICATION (21) Application number : 91302545.8 © int. ci.5 : C07H 5/06, C07H 9/04, C07H 17/04, C07H 15/252, (2) Date of filing : 22.03.91 C07C 229/06, C07C 229/36, C07C 239/18 (§) Priority: 23.03.90 US 498106 (72) Inventor : Wittman, Mark D. 680 Mix Avenue, No. 3F Hamden, Connecticut 06514 (US) (43) Date of publication of application : Inventor : Danishefsky, Samuel J. 09.10.91 Bulletin 91/41 57 Stevenson Road New Haven, Connecticut 06515 (US) Inventor : Halcomb, Randall L. @ Designated Contracting States : 188 Linden Street AT BE CH DE DK ES FR GB GR IT LI LU NL SE New Haven, Connecticut 06511 (US) @ Applicant : YALE UNIVERSITY (74) Representative : Fisher, Adrian John et al 246 Church Street CARPMAELS & RANSFORD 43 Bloomsbury New Haven, CT 06510 (US) Square London WC1A 2RA (GB) @ The conversion of amines to hydroxylamines. (57) Oxidation of primary amines to primary hydroxylamines using a dialkyl dioxirane is described. This new method is utilized to prepare aliphatic non-axial hydroxylamines from corresponding primary amino-substituted sugar derivatives and hydroxylamino acid derivatives. CO CM CO o m Ti- ll. LU Jouve, 18, rue Saint-Denis, 75001 PARIS EP 0 450 823 A2 THE CONVERSION OF AMINES TO HYDROXYLAMINES This invention was made with the support of the Government of the United States of America, and the Gov- ernment of the United States of America has certain rights in the invention. 5 Technical Field The present invention relates to a novel oxidation of a non-axial amine to its corresponding hydroxylamine, and more particularly to the conversion of biologically interesting amines such as those of sugar derivatives and amino acids to their respective, corresponding hydroxyl amines. 10 Background Hydroxylamines are an interesting group of compounds if only because they contain two nucleophilic atoms, nitrogen and oxygen, bonded to each other. Indeed, either of the nucleophilic atoms can take part in 15 nucleophilic reactions, depending upon the reactants and substrates. Still further, the nucleophilicity of hydroxylamines is enhanced over that expected on the basis of their pKa values in what has been termed the "a- effect" [Edwards et al., J. Am. Chem. Soc, 84:16 (1962)]. Aliphatic primary hydroxyl amines; i.e., a hydroxylamine substituted on the nitrogen atom by a single aliphatic organic radical, such as N-methyl hydroxylamine are items of commerce. N-Acylated hydroxyl amines form 20 hydroxamic acids, which can be used in assays for the presence of iron1" ions because of the reddish colored complexes that are formed. Primary hydroxylamines also act as ligands to form complexes with metal ions. Primary hydroxylamines are typically prepared by reaction of hydroxylamine itself with an aldehyde to form an oxime, followed by reduction of the oxime with a mild reducing agent. Primary amines oxidized with Caro's acid (H2S05) typically form the corresponding nitrone that rearranges to an oxime, with the hydroxylamine being 25 a postulated intermediate. Secondary amines oxidized with Caro's acid form secondary hydroxylamines. The usual a-amino acids are also used as ligands to complex with metal ions such as iron. The corresponding a-hydroxylamino acids, and their corresponding hydroximates are also useful as ligands for forming complexes with metal ions such as FeMl. The recently reported calicheamicin [see, Lee et al., J. Am. Chem. Soc, 109:3464 (1987) and the citations 30 therein] and esperamicin [see, (a) Golik et al., J. Am. Chem. Soc, 109:3461 (1987); and (b) Golik et al., J.Am. Chem. Soc, 109:3462 (1987) and the citations therein] antibiotics contain a novel hydroxylamine-substituted glycosidic unit in their oligosaccharide side chains. Inasmuch as the polysaccharide portions of the calicheami- cins and esperamicins appear to direct those antibiotics to DNA molecules where they intercalate and cleave the DNA, it would be of interest to synthesize the hydroxylamine-containing sugar derivatives as well as the 35 entire oligosaccharide portion of an esperamicin or a calicheamicin that could be then bonded to the enediyne portion to form a synthetic esperamicin or calicheamicin or derivative thereof. It would therefore be beneficial if a relatively high yielding, simple synthesis could be devised to form aliphatic primary hydroxylamine compounds. The disclosure below describes one such process for the preparation of aliphatic primary hydroxylamine compounds. 40 Brief Summary of the Invention The present invention contemplates the formation of an aliphatic non-axial hydroxylamine from a corresponding non-axial primary amine, and the hydroxylamine products. This method comprises admixing an 45 excess of an aliphatic non-axial primary amine with a dialkyl dioxirane having a total of two to about six carbon atoms in the dialkyl groups to form a reaction mixture. The reaction mixture is maintained for a time period suf- ficient to form the corresponding hydroxylamine. Particularly preferred aliphatic non-axial primary amine-containing starting materials are substituted sugar derivatives and amino acid derivatives. A particularly preferred dialkyl dioxirane is dimethyl dioxirane. so The present invention has several benefits and advantages. One benefit of the invention is that it provides a ready means for the preparation of primary non-axial hydroxylamines An advantage of the present invention is that primary non-axial hydroxylamines can be produced in compounds having various substituent groups without substantial alteration of those substituents. 55 Another benefit of the invention is that an important intermediate in the synthesis of the esperamicin trisaccharide group can be readily prepared. 2 EP 0 450 823 A2 Still further benefits and advantages will be apparent to a skilled worker from the disclosures that follow. Brief Description of the Drawings 5 in the drawings forming a portion of this disclosure, Figure 1 illustrates the structures of some sugar-substituted primary amines and their corresponding hydroxylamine reaction products. Each reaction shown utilized dimethyl dioxirane o-o < K > as oxidant in an acetone solution at a temperature starting at -45 degrees C, which temperature was permitted to warm to ambient room temperature (RT) over a two-hour time period. In the structures, Ac is acetyl, Bz is 15 benzoyl and Ph is phenyl. Wedge-shaped or heavily blackened bonds are utilized to indicate a bond projecting forward from the plane of the page, whereas dashed bonds indicate bonds projecting behind the plane of the page, following usual practice for such bonds. Figure 2 illustrates further reactants, products for further exemplary oxidations. Here, PMBO represents p-methoxybenzyl. The same reaction conditions were used in the reaction of Figure 2 as for Figure 1. Bonds 20 are as depicted in Figure 1 . Figure 3 illustrates the reactions of the methyl esters of phenylalanine, Compound 14, and valine, Com- pound 16, to their respective hydroxylamine derivatives, Compounds 1[5 and 17. The reaction conditions of Fig- ure 1 were utilized. Bonds are as depicted in Figure 1. Figure 4 illustrates a reaction scheme for the synthesis of a hydroxylamino trisaccharide similar in structure 25 to the esperamicin trisaccharide, but lacking the thioether of that trisaccharide. In this figure, Ph is phenyl, Bn is benzyl, is p-methoxy benzyl, OAc is acetate and H2/Pd is hydrogenation over a palladium catalyst. Figure 5 in two sheets (Figure 5/1 and Figure 5/2) illustrates a reaction scheme for the preparation of an esperamicin trisaccharide, Compound 27, and a chimeric antibiotic, Compound 28, that utilizes that trisaccharide. In this scheme, Pi is 2,4-dinitrophenyl, R, is p-methoxybenzyl, OAc is acetate, Mel is methyl iodide, 30 DDQ is 2,3-dichloro-5,6-dicyano-1 ,4-benzoquinone and ROH is an exemplary aglycone such as daunorubicin or doxorubicin aglycone. Definitions 35 The following words and phrases are utilized herein to have the meanings that are normally recognized in the art and as are described below. The term "sugar" and "sugar derivative" are utilized herein generically to mean a carbohydrate or carbohydrate derivative that contains 5-9 atoms in its backbone chain, and those of interest herein can be a pentose, hexose, heptose, octulose or nonulose. 40 A "monosaccharide" is a simple sugar that cannot be hydrolyzed into smaller units. An "oligosaccharide" is a compound sugar that yields two to about 10 molecules of simple monosaccharide per molecule on hydrolysis. A "polysaccharide" is a compound sugar that yields more than 10 molecules of simple monosaccharide per molecule on hydrolysis. 45 A sugar molecule or its derivative typically contains a plurality of hydrogen, alkyl, hydroxyl, amine or mer- captan groups in free or protected form such as the N-phthalimido group or the S-acetyl group bonded to each of the carbon atoms of the molecular chain. Where the sugar molecule is in cyclic form, the oxygen atom of one of the hydroxyl groups is utilized as the oxygen that is part of the cyclic ring structure. A deoxysugar contains a hydrogen atom or other substituent group in place of one of the hydroxyl groups. 50 Each of the substituents, other than the hydrogen of a deoxysugar, has a particular stereochemical configuration relative to the other substituents and relative to the plane of the cyclic ring. The chain length and stereochemical configuration of the substituent groups provide the basis for the names of the sugars. The sugar molecules and their derivatives utilized herein are of known stereochemical configuration. Position numbering in a sugar molecule begins with the aldehydic carbon for aldoses and the terminal car- 55 bon atom closest to the keto group for ketoses. Thus, for a glycal, the first carbon of the ethylenic unsaturation adjacent the ring oxygen is numbered "position 1", with the remaining positions being numbered around the ring away from the ring oxygen atom.

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