RE: ORGLIST: Reagarding 1, 5 dicarbonyl sugar preparation and its reductive amination

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From: will jones (willjones46$##$hotmail.com)
Date: Wed Nov 30 2005 - 11:45:07 EST


Shailesh

Dont know why you Moffat oxidation isnt working.

With the Swern oxidation, are you keeping your reaction at -78? If not you
can get a mixture of side-products (thioacetals).
Secondly, are you adding your base in at the same time or separately? Add
base in after the initial reaction has taken place.

Regarding your reductive amination, I was, thanks to input from orglist,
converted from using NaCNBH3 to using Na(OAc)3BH as the reducing agent in
all my reductive amination reactions. The reactions appear to be more
reliable. No doubt there are follows of different reductive amination
methods out there, but for me, this is the most useful. give it a try. I
make it in situ by adding 3.5eq. of AcOH to NaBH4 in DMF and then use after
30mins of stirring at 0degC.

As for your purification, I noticed that you had an amine on your final
product. In my experience, amines and silica gel give poor resolution unless
you add TEA, say 1%. This can really increase your resolution. Try that. If
you dont need the protecting groups for your next stage, I would deprotect
and then clean up my product by reverse phase hplc.

Hope that something in here is of use.

cheers

Will


>From: "shailesh patel m" <shailptl$##$rediffmail.com>
>Reply-To: shailesh patel m <shailptl$##$rediffmail.com>
>To: Everybody$##$orglist.net
>Subject: ORGLIST: Reagarding 1,5 dicarbonyl sugar preparation and its
>reductive amination
>Date: 30 Nov 2005 14:49:02 -0000
>
>Deal all,
>I have been working in the project involving Tetra O-benzyl
>Deoxynojirimycin (Bn4DNJ)synthesis.
>
>Its synthesis includes double Pftizner-Moffat oxidation as given in the
>paper "Synthesis, 1999, No. 4, 571-573"
>
>I am facing problem like
>
>1) Oxidation was not giving clear cut reaction. I have tried swern
>oxidation as well.Reaction was not going to completion when I used reported
>quantity of DMSO/TFAA. Increasing quantity did not make much difference.
>
>2) Purification was really very very turf. Can anybody suggest me the
>method of purification in detail which will give me satisfactory results.I
>am using the silica 60/120 mesh(Ethyl acetate : Hexane)(5:95)everything
>comes out on conventional chromatography. I have tried neutral silica and
>Alumina as well.No separation and huge loss in the column purification with
>this protocol.
>
>3) Generally for the sugar derivative which stationary phase is used ?
>
>For your ready reference I have attached scheme involved for your ready
>reference.
>
>Looking for your co-operation.
>
>Shailesh


><< Orglist_scheme.doc >>


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