Entity Framework (Database first) - Include DataAnnotations

I saw in an MS link that it is possible to create a partial and a Metadata class to include DataAnnotations in properties created by the Entity Framework (database first). Well, I did as the example, but the application has an error:

  

The metadata type associated with type 'Context.CONTEUDO' contains the following unknown properties or fields: CONTENT. Make sure the names of these members match the names of the properties in the parent type.

I will send the code of the 3 classes (generated by EF, metadata and partial):

// EF scaffolding
namespace Context
{
    using System;
    using System.Collections.Generic;

    public partial class CONTEUDO
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public CONTEUDO()
        {
            this.CONTEUDOS = new HashSet<CONTEUDO>();
            this.CONTEUDO_ANEXO = new HashSet<CONTEUDO_ANEXO>();
            this.CONTEUDO_PERMISSOES = new HashSet<CONTEUDO_PERMISSOES>();
        }

        public int COD_CONTEUDO { get; set; }
        public Nullable<int> COD_CONTEUDO_PAI { get; set; }
        public int COD_EBOOK { get; set; }
        public string TITULO { get; set; }
        public string TEXTO { get; set; }
        public Nullable<System.DateTime> CRIADO_EM { get; set; }
        public int CRIADO_POR { get; set; }
        public System.Guid UNIQUE_ID { get; set; }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<CONTEUDO> CONTEUDOS { get; set; }
        public virtual CONTEUDO CONTEUDO_PAI { get; set; }
        public virtual USUARIO USUARIO { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<CONTEUDO_ANEXO> CONTEUDO_ANEXO { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<CONTEUDO_PERMISSOES> CONTEUDO_PERMISSOES { get; set; }
        public virtual EBOOK EBOOK { get; set; }
    }
}

// Metadata
namespace Context
{
    public class ConteudoMetadata
    {
        [Required]
        [Range(1, 999999)]
        [Display(Name = "Ebook")]
        public int COD_EBOOK;

        [Required]
        [Display(Name = "Título")]
        public string TITULO;

        [Required]
        [Display(Name = "Conteúdo")]
        public string CONTEUDO;
    }
}

// Partial com MetadataType attribute
namespace Context
{
    [MetadataType(typeof(ConteudoMetadata))]
    public partial class CONTEUDO
    {
    }
}

It's all in the same namespace, so there's no problem, but it does not work.