Synthesis of a Water-soluble Metal–Organic Complex Array

Summary

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

Abstract

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

Introduction

Controlled synthesis of complicated molecular structures has always been a major issue in synthetic chemistry. From this point of view, to synthesize multinuclear heterometallic complexes in a designable fashion is still a worthy subject to be challenged in the field of inorganic chemistry because of the numbers of possible structural outcomes from the ligand-metallation-based approach that is commonly used for the preparation of monomeric metal complexes. Although several examples of multinuclear heterometallic complexes have been reported so far^1,2,3, the trial-and-error or arduous nature of their synthesis necessitates the development of a simple method ....

Protocol

1. Preparation of Metal Complex Monomers (2 CAS RN 1381776-70-0, 3 CAS RN 1261168-42-6, 4 CAS RN 1261168-43-7; Figure 1)

1. Preparation of Ru monomer 2
   1. Combine the organic precursor (5⁹ CAS RN 1381776-63-1; Figure 1) (380 mg, 0.48 mmol) and [Ru(p-cymene)Cl₂] dimer (224 mg, 0.37 mmol) with a stir bar in a 100 ml single-neck round-bottom flask.
   2. Add methanol (MeOH) (25 ml) to the mixture, connect a condenser to the joint of the flask, and stir the suspension at 65 °C for 3 hr in a temperature-controlled oil bath.
   3. Cool the reaction mixture to r....

Results

Figure 1 shows the molecular structures of the final target compound, precursors, and intermediates. Figure 2 shows the images of the resin and Figure 3 shows the MALDI-TOF mass spectra of samples at selected procedure steps. Images from Figure 2a to 2h show the changes in the color and appearance of the resin that it undergoes during the reaction steps in section 2 of the protocol. MALDI-TOF mass spectro.......

Discussion

Perfect removal of the undesired chemicals from the resin is not always possible simply by washing with solvents that can easily dissolve those chemicals. A key technique to efficiently wash the resin is to cause it to swell and shrink repetitively so that the chemicals remaining inside will be forced out. This is why the resin in our procedure is treated with CH₂Cl₂ and MeOH alternately as it is washed (e.g., protocol 2.1.4).

As a consequence of successive multi.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Dichloro(1,5-cyclooctadiene)platinum(II)	TCI	D3592
Rhodium(III) chloride trihydrate	Kanto Chemical	36018-62
Phosphate buffered saline, tablet	Sigma Aldrich	P4417-50TAB
NovaSyn TG Sieber resin	Novabiochem	8.55013.0005
HBTU	TCI	B1657
Benzoic anhydride	Kanto Chemical	04116-30
Trifluoroacetic acid	Kanto Chemical	40578-30
Triethylsilane	TCI	T0662
2-[2-(2-Methoxyethoxy)ethoxy]acetic acid	Sigma Aldrich	407003	Dried over 3 Å sieves
Dithranol	Wako Pure Chemical Industries	191502
N-methylimidazole	TCI	M0508
Piperidine	Kanto Chemical	32249-30
4'-(4-methylphenyl)-2,2':6',2"-terpyridine	Sigma Aldrich	496375
Dehydrated grade dimethylsulfoxide	Kanto Chemical	10380-05
Dehydrated grade methanol	Kanto Chemical	25506-05
Dehydrated grade dichloromethane	Kanto Chemical	11338-84
MeOH	Kanto Chemical	25183-81
Dimethylsulfoxide	Kanto Chemical	10378-70
Ethyl acetate	Kanto Chemical	14029-81
Acetonitrile	Kanto Chemical	01031-70
1,2-dichloroethane	Kanto Chemical	10149-00
Diethyl ether	Kanto Chemical	14134-00
Dichloromethane	Kanto Chemical	10158-81